It is bonkers that sunscreen (edit: SPF) testing still requires testing on a human subject, which makes testing both expensive and unreliable. Michelle Wong, who is quoted in the article as Lab Muffin Beauty Science, discusses it in more detail for a previous scandal, this one for a Korean sunscreen brand:
It's not side-effects that are in question here, it's the intended effect. When it comes to its effectiveness at blocking UV, there should be a better way than just "apply some to a dozen random volunteers and time how long it takes before they get a sunburn".
In my imagination, the lab would have some a testing process that spreads a precisely-controlled volume over a standard surface area, textured to be similar to skin, then measures UV transmission percentage vs wavelength with a diffraction grating and photocell. Or something like that!
> In my imagination, the lab would have some a testing process that spreads a precisely-controlled volume over a standard surface area, textured to be similar to skin, then measures UV transmission percentage vs wavelength with a diffraction grating and photocell. Or something like that!
With this approach, how would you measure the effectiveness of the sunscreen when it's been absorbed by the skin (which is necessary for the sunscreen to work properly - that's why they always say to wait ten minutes after applying before going out into the sun)?
There's a reason in vitro and in vivo are both studied for clinical trials of medications. Sunscreen isn't any different: you're using a product making a specific claim about a clinical outcome, so that needs to be tested.
> With this approach, how would you measure the effectiveness of the sunscreen when it's been absorbed by the skin
You can eliminate the "can't possibly work" cases much faster and cheaper.
More importantly, it is cheap enough to be always used as a baseline verification when human testing is so expensive that it can only be used as a random sample double-check.
It's like unit testing vs full user acceptance testing. You can and should do both, but the latter isn't for every PR.
IDK. There are tons of things that can happen on (and in importantly for sunscreen) human skin. (Skin sweats in the hot sun, but of course your skin can have various reactions to and with chemical) This seems like the simplest and most effective method for testing effectiveness (should probably come up with some other tests for carcinogenic properties though)
The problem is that testing has to be reproducible but usage doesn't.
I've actually been a test subject for sunscreen here in Australia. It involved having sunscreen put on different parts of your body, hopping into a Jacuzzi for an hour or so, then being zapped with UV on both sunscreened and clear skin.
The testing here is not just that it is safe on skin, but the SPF test itself is done by slathering it on humans and exposing them to light to determine a rating.
If you look at the skin as a protective barrier, then that makes sense, but its ability to absorb cosmetics depends on a lot of factors. First off, what makes a product more absorbable (i.e. influence percutaneous absorption)? Molecular size (typically smaller than ~500 Daltons). Lipophilicity (fat-solubility). Formulations and vehicle, e.g. emulsions (oil-in-water, water-in-oil) can improve penetration depending on balance. There are alcohol-based solutions that enhance delivery of certain actives but may irritate. There are other penetration enhancers such as propylene glycol, ethanol, fatty acids, which disrupt the skin barrier slightly to allow deeper diffusion. Heck, even salicylic acid does that.
There are a lot of other factors here, such as your skin's condition (hydrated skin absorbs better), damaged or inflamed skin even more but sometimes to unsafe levels and it is typically contraindicated for almost all cosmetics.
In any case, most cosmetic ingredients act locally (i.e. not supposed to enter into systemic circulation like transdermal drugs), improve hydration, texture, and/or appearance by altering the stratum corneum or slightly beyond. Systemic absorption is limited unless specifically engineered to do so, such as nicotine patches, hormone creams, fentanyl patches, etc. I mentioned this below "transdermal drug delivery".
The curious should look up the differences between cosmetic absorption vs. transdermal drug delivery as well. For example, cosmetics are not intended to penetrate into the bloodstream, hence the surface layer depth. To give you percentages, typically >90% remains on skin surface, but it also depends on what you want to achieve, because for example hyaluronic acid in creams are of large molecule (~3000-5000 Da), meaning it essentially 0% penetrates. It hydrates only by trapping water on the skin surface. Important to note here that sometimes this is exactly what people want, i.e. this surface hydration is what gives the "plump, glowing skin" effect people expect, so if the goal is hydration and surface smoothness, then large HA is ideal (surface action is enough), but if the goal is true wrinkle reduction or anti-aging, then surface HA alone is not sufficient. This is why companies combine HA with retinoids, peptides, or vitamin C, which act deeper and can influence collagen production. If the goal is long-term structural change, then you can have injectables (such as dermal fillers, which are being used for enlarging the lips, for one).
Transdermal Drug Delivery on the other hand are supposed to enter the bloodstream so drugs delivered through skin (e.g., nicotine, fentanyl, estradiol patches) are engineered to bypass the stratum corneum barrier. They use optimized molecular size, solubility, enhancers, and occlusion. If you want percentages here as well, I would say 20-95% systemic absorption of applied dose, but it depends on a couple of factors I have previously mentioned.
Just to stay on topic: sunscreens require only surface layer depth of absorption only, and in fact, many products work at this level. Their effectiveness depends heavily on formulation, proper application, and reapplication. Sunscreens do work when used correctly, they significantly reduce UV damage, premature aging, and skin cancer risk, BUT you must apply it properly and reapply often. You should combine with shade, too.
I have absolutely zero knowledge about the science and/or biology of skin, I read your post expecting it to end with something stupid like "don't know, I made all of this up". I'm glad it didn't!
I love HN because, for every snarky comment that's made or said on a misunderstood, or incorrect basis of knowledge that would set off an alarm on QI, followed by a stern telling off by Stephen Fry.
There's some one like you, who has an endless pit of knowledge to aritculate or better inform with a whole lot of insight thrown in for good measure. Thank you, your post's awesome. :)
Small edit: I immediately thought "Your skin can't be that good as a barrier, nicotine and caffeine patches work through the skin?" when I saw the post you replied to, and loved that you made reference to it too.
> "95% of the sunscreens tested [by Choice] have high enough SPF to more than halve the incidence of skin cancer," Dr Wong said.
I found this surprising; is halving the incidence of cancer enough to consider it safe? I would expect 90 or 95% reduction in the incidence of cancer to be considered safe.
This reminds me of the study done in Japan of the long term success rate of CPR for cardiac arrest patients, both out and in hospital. I believe it was around 15%, meaning they were still alive after 30 days and did not suffer a significant reduction in quality of life such as stroke.
The actual difference between (say) SPF 30 and 50 is not a lot, 96.7% UV filtering vs 98% but I’m not 100% sure how that translates to actual rates of cancer.
However the worst offenders in the testing advertised SPF 50 but delivered SPF 4 (~75% AFAICT)
In both cases though the level of UV will be easily tolerated, which is the entire point. UV index is a linear scale, so more SPF has rapidly diminishing returns even in places with a UV index of 15+.
That the duration of protection is independent of SPF makes this particularly true. There are only a handful of places in the world where atmospheric conditions might give a very high SPF marginal benefits.
There have been cases of benzene being detected in sunscreen. It's not an intentional ingredient, just one that is common in industrial manufacturing. I don't think that's what the parent was worried about though.
No, benzene was specifically what I was thinking of to the point that I assumed it was so well known that it wasn't question as being a thing any more. Just like asbestos in baby powder
That’s thankfully no longer really a thing - the world has realised that there is no such thing as asbestos-free talc, so baby powder is now mostly corn-starch AFAICT.
> The actual difference between (say) SPF 30 and 50 is not a lot, 96.7% UV filtering vs 98% but I’m not 100% sure how that translates to actual rates of cancer.
Counterintuitively, higher SPF matters a _lot_. The difference is in the _durataion_ of the protection and in the amount of sloppiness you can afford while applying the cream.
Suppose that for you the half-life for the sunscreen is 1 hour. SPF 30 cream would thus decay to SPF 7 in 2 hours, providing little protection. But an SPF 90 cream would still offer quite reasonable SPF 25 protection.
The same applies to sloppiness. SPFs are measured in perfect conditions, with a prescribed amount of the cream spread evenly. So the higher the SPF, the more mistakes you can make while applying it.
Would different SPF sunscreens have same half-life? I have not dig into it, but I would think there is a few mechanism or chemicals and those would have different halflifes.
When I got surfing lessons last summer, all the instructors agreed that sunscreen is pointless. Technically it works but you’re in Queensland, you’re either gonna sweat or get wet, and then it doesn’t.
They all swore by zinc, rashies, and wide brim surf hats. 60 year old Trevor who surfs every day and has never had a mole might just be lucky but somehow I doubt it.
> That rage grew when she learned the sunscreen she had been using for years was unreliable and, according to some tests, offered next to no sun protection at all.
If it wasn't working at all, wouldn't you notice getting sun burned?
Initially i thought it was going to be something advertised as spf 30 but actually 15. However spf 4 or less seems so low it should be noticable i would assume.
SPF doesn’t mean what people think it does. The level of protection is something like (1 - (1 / SPF)), such that the difference in marginal protection between SPF 15 and SPF 30 is literally only a few percent. While SPF 4 sounds “low”, it is already providing you 75% of the maximum possible protection.
The returns on protection are very much diminishing by SPF 30.
As others have mentioned, the difference between 75% (SPF 4) and 96% (SPF 30) might seem small, but the latter implies you can stay in the sun 7.5 times as long before getting sunburnt. That's significant. Moreover sunscreen rapidly loses effectiveness, so having "extra" protection might be worth it, especially if you don't reapply every 2 hours or after sweating/swimming, which what most sunscreens recommend.
The duration of protection is independent of SPF. There is no implication that you can stay in the sun longer with a higher SPF (FWIW, the packaging more or less makes this clear). The only thing SPF represents is a marginal reduction in total UV flux during the protected period.
Anything over SPF 30 buys you approximately no additional protection.
It's like an error rate. If you write code where 99 of the lines of code are correct out of a 100, your code is twice as robust as a programmer writing 98 correct lines.
What is of interest is not the blocking percentage, but the transmission percentage.
According to WikiPedia:
"For example, "SPF 15" means that 1⁄15 of the burning radiation will reach the skin, assuming sunscreen is applied evenly at a thick dosage of 2 milligrams per square centimeter[67] (mg/cm2)."
so assuming a linear dose response relationship (obviously oversimplified) when not using the sunscreen 15 times more instantaneous random damage is incurred compared to when using the sunscreen.
This does not translate directly into the rate of cancers though: just like the final damage of a meteorite storm isn't proportional, even though the instantaneous damage is.
Suppose a meteorite strikes a hospital, lots of damage. Then years later a meteorite strikes a school, lots of damage. Obviously if both happen in quick succession more damage will occur.
But if the whole human population takes up sunscreen use, selective pressure on cellular coping mechanisms will be relaxed, and eventually future generations won't be as resilient against sunburn. So just live your life, and don't allow scaremongers to separate you from your money, or thus indirectly scare you into doing your job for them.
So SPF 4 you are letting 25% of the sun through. I would assume that would be enough to still be sun burnt on a high uv index day if you spend most of it on the beach.
My impression of Neutrogena too, despite them testing well in NZ. Nivea is cheap, basic and actually works.
Absolutely hate mineral ones, literally worst of all worlds - expensive, bad ux and doesn’t work. All while greenwashing. So much so it became my litmus to test people’s literacy.
I use the spf 50 ‘sport’ version on my legs and arms (not the face, too greasy) and it seems to do the job OK.
I guess if it’s 35 in testing that’s still OK-ish for general use. I do really plaster it on. And as I’m usually doing that before a lot of outdoor work, it draws a further protective layer of sand and dirt to itself…
As an aussie kid I bought into the whole sunscreen hype, but after more than half a dozen failures/partial failures. I've pretty much given up on the stuff (excluding areas that are difficult to protect fully with coverings, neck/face/etc).
Long sleeve thick cotton shirts, long pants, and a good wide brimmed hat are easily ten times more effective in practice. My old hard as a tack, shearer grandfather used to swear by black picnic umbrellas (great option if you are spending time working in a fixed location).
Of course you can't swim that well in long sleeved clothes hence the popularity of sunscreen. I'm totally against Aussie beaches at this point though, yes they are nice and all but the radiation dose is just nuts.
Would love to see something like the Apple Watch include UV dosimeter functionality.
"I’ve always felt sunscreen never lives up to its promise."
I agree with that for the same reasons. Nevertheless, I'll still use sunscreen when I have to. In Australia there are times when it's hard to avoid the sun but I avoid it at every opportunity.
If at the end of a day I feel my skin the slightest bit sore from exposure I know I've not been proactive enough.
Maybe it’s inconvenient, but for me the promise is sun protection, and for that it for sure works.
Spray goes on easier, not only does spray cover area, but it spreads easier than cream too, but anything is better than nothing. But I have drifted towards preferring long sleeves, hats, and even a sun umbrella so I don’t have to get greased up.
In Australia here. I tend to go morning or 3pm. Crowds reduce, UV is lower, sun goes down 8pm in summer (so 3-8 is 5 hours). Anything near midday is silly.
Hill country TX where 8 month out of the year are 35 C daily and way too much humidity.
Agreed, partially. There are times one has to do things when it's blazing hot.
On sunscreens, we're still missing:
- amiloxate
- bemotrizinol
- bisdisulizole disodium
- bisoctrizole
- drometrizole trisiloxane
- tris-biphenyl triazine
While continuing to allow:
- 4-MBC (enzacamene)
- avobenzone
- oxybenzone
- homosalate
- octinoxate
- octocrylene
In the US, buying a safe(r) (for humans and reefs) sunscreen requires a medical and a marine biology degree unless you're willing to slather yourself in white pastes like zinc oxide or titanium dioxide. One major barrier is the law demands animal testing prior to approval.
Meanwhile, there are still millions of Americans (mostly men) who routinely venture outdoors for work and projects without sufficient protection and accumulate enough exposure that leads to preventable skin cancer. And I had my fair share of sunburns as an active kid.
If a product can pass for years and then fail, the real problem is the trust gap. The fix is boring but workable: clear test methods, lot-level results, independent re-tests, and recalls when needed. Without that, consumers can’t tell good from bad.
Wait until you learn that some of the sunscreens sold (can't say specifically in Australia, but I know this is the case in the US) only block UVB, so you won't get a sunburn but you will still get exposed to unhealthy amounts of UVA. Basically sunscreen is often optimized to not make you burn, which burning might actually be a good thing since it's preventing you from getting exposed to even more UVA.
Note that I didn't look into this paper in detail. I just used searched for "cold climate high intelligence" and picked the first result after checking the abstract.
What is also awful was the number of "influencers" aka digital door-to-door salespersons pushing that Ultra Violette sun screen slop on TT and Insta.
There is no repercussions for these clowns pushing a faulty product into the masses. I guess they actually are the winners here because they walk away with cash while their followers end up with shitty product and the company has to deal with the fallout. I doubt the digital door-to-door salespersons reputation suffers as their audience will still lap up anything they sell like a thirsty dog in the desert.
Everyone in Australia gets skin cancer. It's just normal. My grandma had something like 5 or 10 of them removed. In general, kids these days spend less time outside and do understand the value of hats and sunscreen or long sleeves, so it's getting better. The face can be hard, particularly without a hat.
I always laugh when people wear those stupid baseball caps instead of proper hats with brims. They think it's 'cool'. Mate, the main person laughing at your 'cool' is future you - dying from skin cancer on your face.
I can't speak for Australia, but in general you definitely don't need to burn for increased cancer risk - a clear example of that is the fact that artificial UV tanning beds lead to significantly increased rates of cancer despite the fact that they're used in such a way that you tan without going far enough to burn.
Although we often think of burning as bad and tanning as good, tanning is nonetheless still actually a symptom of your skin being damaged by the sun - it's just a symptom that looks better than burned skin, to the point that many people think it looks nice enough to be worth the cancer risk (and/or don't understand the risk when they decide to tan).
Technically both of these approaches are not as good as a wide brimmed hat in terms of face protection. However, for some sports it's superior (anything with wind or clearance issues). I'm on a Stetson at the moment after a US trip but usually go for whatever broad brim is available. Buying new ones gets old so going for a 'crushable' model is the go - I like the felt Stetsons. The other benefit from a broad brim is it functions as an auto-umbrella in light weather which is damn cool. Also, hat-on-face is similar to those plane-sleep-eyewear bands.
It is bonkers that sunscreen (edit: SPF) testing still requires testing on a human subject, which makes testing both expensive and unreliable. Michelle Wong, who is quoted in the article as Lab Muffin Beauty Science, discusses it in more detail for a previous scandal, this one for a Korean sunscreen brand:
https://labmuffin.com/purito-sunscreen-and-all-about-spf-tes...
You’re kidding? You want millions of people to apply something that gets absorbed into the skin without testing it for side effects?
It's not side-effects that are in question here, it's the intended effect. When it comes to its effectiveness at blocking UV, there should be a better way than just "apply some to a dozen random volunteers and time how long it takes before they get a sunburn".
In my imagination, the lab would have some a testing process that spreads a precisely-controlled volume over a standard surface area, textured to be similar to skin, then measures UV transmission percentage vs wavelength with a diffraction grating and photocell. Or something like that!
> In my imagination, the lab would have some a testing process that spreads a precisely-controlled volume over a standard surface area, textured to be similar to skin, then measures UV transmission percentage vs wavelength with a diffraction grating and photocell. Or something like that!
With this approach, how would you measure the effectiveness of the sunscreen when it's been absorbed by the skin (which is necessary for the sunscreen to work properly - that's why they always say to wait ten minutes after applying before going out into the sun)?
There's a reason in vitro and in vivo are both studied for clinical trials of medications. Sunscreen isn't any different: you're using a product making a specific claim about a clinical outcome, so that needs to be tested.
"that's why they always say to wait ten minutes after applying before going out into the sun"
They don't always say that. Some say explicitely that it provides instant protection. (there are different ways, that sunscreen provides protection)
> With this approach, how would you measure the effectiveness of the sunscreen when it's been absorbed by the skin
You can eliminate the "can't possibly work" cases much faster and cheaper.
More importantly, it is cheap enough to be always used as a baseline verification when human testing is so expensive that it can only be used as a random sample double-check.
It's like unit testing vs full user acceptance testing. You can and should do both, but the latter isn't for every PR.
IDK. There are tons of things that can happen on (and in importantly for sunscreen) human skin. (Skin sweats in the hot sun, but of course your skin can have various reactions to and with chemical) This seems like the simplest and most effective method for testing effectiveness (should probably come up with some other tests for carcinogenic properties though)
The problem is that testing has to be reproducible but usage doesn't.
I've actually been a test subject for sunscreen here in Australia. It involved having sunscreen put on different parts of your body, hopping into a Jacuzzi for an hour or so, then being zapped with UV on both sunscreened and clear skin.
Easiest hundred bucks I ever made, gotta say.
You get paid for an hour in the jacuzzi? Sign me up ;)
How did they measure the effectiveness of the sunscreen and any side effects on your skin?
The testing here is not just that it is safe on skin, but the SPF test itself is done by slathering it on humans and exposing them to light to determine a rating.
You're kidding? You equate "not testing on human subject" to "not testing"?
Skin doesn’t just absorb things. In fact it’s incredibly good at resisting so much so that most beauty products are complete BS.
If you look at the skin as a protective barrier, then that makes sense, but its ability to absorb cosmetics depends on a lot of factors. First off, what makes a product more absorbable (i.e. influence percutaneous absorption)? Molecular size (typically smaller than ~500 Daltons). Lipophilicity (fat-solubility). Formulations and vehicle, e.g. emulsions (oil-in-water, water-in-oil) can improve penetration depending on balance. There are alcohol-based solutions that enhance delivery of certain actives but may irritate. There are other penetration enhancers such as propylene glycol, ethanol, fatty acids, which disrupt the skin barrier slightly to allow deeper diffusion. Heck, even salicylic acid does that.
There are a lot of other factors here, such as your skin's condition (hydrated skin absorbs better), damaged or inflamed skin even more but sometimes to unsafe levels and it is typically contraindicated for almost all cosmetics.
In any case, most cosmetic ingredients act locally (i.e. not supposed to enter into systemic circulation like transdermal drugs), improve hydration, texture, and/or appearance by altering the stratum corneum or slightly beyond. Systemic absorption is limited unless specifically engineered to do so, such as nicotine patches, hormone creams, fentanyl patches, etc. I mentioned this below "transdermal drug delivery".
The curious should look up the differences between cosmetic absorption vs. transdermal drug delivery as well. For example, cosmetics are not intended to penetrate into the bloodstream, hence the surface layer depth. To give you percentages, typically >90% remains on skin surface, but it also depends on what you want to achieve, because for example hyaluronic acid in creams are of large molecule (~3000-5000 Da), meaning it essentially 0% penetrates. It hydrates only by trapping water on the skin surface. Important to note here that sometimes this is exactly what people want, i.e. this surface hydration is what gives the "plump, glowing skin" effect people expect, so if the goal is hydration and surface smoothness, then large HA is ideal (surface action is enough), but if the goal is true wrinkle reduction or anti-aging, then surface HA alone is not sufficient. This is why companies combine HA with retinoids, peptides, or vitamin C, which act deeper and can influence collagen production. If the goal is long-term structural change, then you can have injectables (such as dermal fillers, which are being used for enlarging the lips, for one).
Transdermal Drug Delivery on the other hand are supposed to enter the bloodstream so drugs delivered through skin (e.g., nicotine, fentanyl, estradiol patches) are engineered to bypass the stratum corneum barrier. They use optimized molecular size, solubility, enhancers, and occlusion. If you want percentages here as well, I would say 20-95% systemic absorption of applied dose, but it depends on a couple of factors I have previously mentioned.
Just to stay on topic: sunscreens require only surface layer depth of absorption only, and in fact, many products work at this level. Their effectiveness depends heavily on formulation, proper application, and reapplication. Sunscreens do work when used correctly, they significantly reduce UV damage, premature aging, and skin cancer risk, BUT you must apply it properly and reapply often. You should combine with shade, too.
I have absolutely zero knowledge about the science and/or biology of skin, I read your post expecting it to end with something stupid like "don't know, I made all of this up". I'm glad it didn't!
I love HN because, for every snarky comment that's made or said on a misunderstood, or incorrect basis of knowledge that would set off an alarm on QI, followed by a stern telling off by Stephen Fry.
There's some one like you, who has an endless pit of knowledge to aritculate or better inform with a whole lot of insight thrown in for good measure. Thank you, your post's awesome. :)
Small edit: I immediately thought "Your skin can't be that good as a barrier, nicotine and caffeine patches work through the skin?" when I saw the post you replied to, and loved that you made reference to it too.
> "95% of the sunscreens tested [by Choice] have high enough SPF to more than halve the incidence of skin cancer," Dr Wong said.
I found this surprising; is halving the incidence of cancer enough to consider it safe? I would expect 90 or 95% reduction in the incidence of cancer to be considered safe.
Considering that sunscreen in general is pretty garbage at blocking UVA, it isn't nearly as effective as traditional methods like a hat and a shirt.
This reminds me of the study done in Japan of the long term success rate of CPR for cardiac arrest patients, both out and in hospital. I believe it was around 15%, meaning they were still alive after 30 days and did not suffer a significant reduction in quality of life such as stroke.
Yeah it’s not really enough.
The actual difference between (say) SPF 30 and 50 is not a lot, 96.7% UV filtering vs 98% but I’m not 100% sure how that translates to actual rates of cancer.
However the worst offenders in the testing advertised SPF 50 but delivered SPF 4 (~75% AFAICT)
You can't compare the straight percentage, a 98% filter lets through twice as much as a 99% filter.
In both cases though the level of UV will be easily tolerated, which is the entire point. UV index is a linear scale, so more SPF has rapidly diminishing returns even in places with a UV index of 15+.
That the duration of protection is independent of SPF makes this particularly true. There are only a handful of places in the world where atmospheric conditions might give a very high SPF marginal benefits.
True, so the important factor is - how does this map to your chances of getting skin-cancer?
The most reasonable answer is to look at the transmission percentage, not the blocking percentage.
But what about the sunscreen with ingredients that are carcinogenic before you even need to consider UV protection?
Yes that would be serious so I suppose in an actual specific case regarding some specific real ingredients in products, we could discuss that.
There have been cases of benzene being detected in sunscreen. It's not an intentional ingredient, just one that is common in industrial manufacturing. I don't think that's what the parent was worried about though.
https://www.ewg.org/sunscreen/beware-of-benzene-shining-a-li...
No, benzene was specifically what I was thinking of to the point that I assumed it was so well known that it wasn't question as being a thing any more. Just like asbestos in baby powder
That’s thankfully no longer really a thing - the world has realised that there is no such thing as asbestos-free talc, so baby powder is now mostly corn-starch AFAICT.
If you drive gas car there’s far more benzene around you than in sunscreen.
I mean, that’s a whole separate question really. Alongside which constituents may be long-lasting and harmful to (for example) marine life.
> The actual difference between (say) SPF 30 and 50 is not a lot, 96.7% UV filtering vs 98% but I’m not 100% sure how that translates to actual rates of cancer.
Counterintuitively, higher SPF matters a _lot_. The difference is in the _durataion_ of the protection and in the amount of sloppiness you can afford while applying the cream.
Suppose that for you the half-life for the sunscreen is 1 hour. SPF 30 cream would thus decay to SPF 7 in 2 hours, providing little protection. But an SPF 90 cream would still offer quite reasonable SPF 25 protection.
The same applies to sloppiness. SPFs are measured in perfect conditions, with a prescribed amount of the cream spread evenly. So the higher the SPF, the more mistakes you can make while applying it.
Would different SPF sunscreens have same half-life? I have not dig into it, but I would think there is a few mechanism or chemicals and those would have different halflifes.
Certainly, but the same principle still applies. Higher SPF will provide more headroom for a given chemistry.
When I got surfing lessons last summer, all the instructors agreed that sunscreen is pointless. Technically it works but you’re in Queensland, you’re either gonna sweat or get wet, and then it doesn’t.
They all swore by zinc, rashies, and wide brim surf hats. 60 year old Trevor who surfs every day and has never had a mole might just be lucky but somehow I doubt it.
[delayed]
> That rage grew when she learned the sunscreen she had been using for years was unreliable and, according to some tests, offered next to no sun protection at all.
If it wasn't working at all, wouldn't you notice getting sun burned?
Initially i thought it was going to be something advertised as spf 30 but actually 15. However spf 4 or less seems so low it should be noticable i would assume.
SPF doesn’t mean what people think it does. The level of protection is something like (1 - (1 / SPF)), such that the difference in marginal protection between SPF 15 and SPF 30 is literally only a few percent. While SPF 4 sounds “low”, it is already providing you 75% of the maximum possible protection.
The returns on protection are very much diminishing by SPF 30.
As others have mentioned, the difference between 75% (SPF 4) and 96% (SPF 30) might seem small, but the latter implies you can stay in the sun 7.5 times as long before getting sunburnt. That's significant. Moreover sunscreen rapidly loses effectiveness, so having "extra" protection might be worth it, especially if you don't reapply every 2 hours or after sweating/swimming, which what most sunscreens recommend.
The duration of protection is independent of SPF. There is no implication that you can stay in the sun longer with a higher SPF (FWIW, the packaging more or less makes this clear). The only thing SPF represents is a marginal reduction in total UV flux during the protected period.
Anything over SPF 30 buys you approximately no additional protection.
The instantaneous damage is directly inversely proportional to SPF.
Using no sunscreen is SPF 1 (at 2 milligrams per square cm). Sunscreen SPF 2 would correspond to halving the rate of instantaneous damage.
SPF 30 compared to SPF 4 would indeed give (30/4)=7.5 times lower rate of instantaneous damage.
The SPF scale is more sensible than your blocking percentage scale.
The dose response is not linear, there is no “instantaneous damage” below some threshold. Your argument assumes something that isn’t true.
As with most things, the dose makes the poison.
It's like an error rate. If you write code where 99 of the lines of code are correct out of a 100, your code is twice as robust as a programmer writing 98 correct lines.
What is of interest is not the blocking percentage, but the transmission percentage.
According to WikiPedia:
"For example, "SPF 15" means that 1⁄15 of the burning radiation will reach the skin, assuming sunscreen is applied evenly at a thick dosage of 2 milligrams per square centimeter[67] (mg/cm2)."
so assuming a linear dose response relationship (obviously oversimplified) when not using the sunscreen 15 times more instantaneous random damage is incurred compared to when using the sunscreen.
This does not translate directly into the rate of cancers though: just like the final damage of a meteorite storm isn't proportional, even though the instantaneous damage is.
Suppose a meteorite strikes a hospital, lots of damage. Then years later a meteorite strikes a school, lots of damage. Obviously if both happen in quick succession more damage will occur.
But if the whole human population takes up sunscreen use, selective pressure on cellular coping mechanisms will be relaxed, and eventually future generations won't be as resilient against sunburn. So just live your life, and don't allow scaremongers to separate you from your money, or thus indirectly scare you into doing your job for them.
However across millions of people over lifetimes may offer substantial increase in incident reduction no?
Sure but this is talking about n of 1
I mean, that is what i thought it meant.
So SPF 4 you are letting 25% of the sun through. I would assume that would be enough to still be sun burnt on a high uv index day if you spend most of it on the beach.
what a tremendous failure on a regulation level
Anecdata on QLD everyone knows banana boat is a scam. That sunscreen straight doesn’t work. The cancer council being on here is surprising though
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Ok I found this handy chart on a guardian article: https://www.theguardian.com/australia-news/2025/jun/12/sever...
According to the chart it's not even that bad? Sure, it underperformed its claimed SPF, but it's still above median.
Yeah I think it’s the water resistance, I bet it way below par
"I bet it way below par"
Thanks, that is a great observation
I use Banana Boat sunscreen, they have many different types. The water resistance depends on which type you use
From the article, it seems like they might all use the same supplier for the active ingredient.
My impression of Neutrogena too, despite them testing well in NZ. Nivea is cheap, basic and actually works.
Absolutely hate mineral ones, literally worst of all worlds - expensive, bad ux and doesn’t work. All while greenwashing. So much so it became my litmus to test people’s literacy.
It works ok for me in Perth :shrug:
I use the spf 50 ‘sport’ version on my legs and arms (not the face, too greasy) and it seems to do the job OK.
I guess if it’s 35 in testing that’s still OK-ish for general use. I do really plaster it on. And as I’m usually doing that before a lot of outdoor work, it draws a further protective layer of sand and dirt to itself…
I’ve always felt sunscreen never lives up to its promise.
It’s tedious to apply thoroughly. It loses effectiveness with water, sweat, etc — inevitable when outside.
It would work best in indoor conditions but then wouldn’t be needed…
I suppose I could sun bathe on a cool winter day … but that just isn’t fun.
As an aussie kid I bought into the whole sunscreen hype, but after more than half a dozen failures/partial failures. I've pretty much given up on the stuff (excluding areas that are difficult to protect fully with coverings, neck/face/etc).
Long sleeve thick cotton shirts, long pants, and a good wide brimmed hat are easily ten times more effective in practice. My old hard as a tack, shearer grandfather used to swear by black picnic umbrellas (great option if you are spending time working in a fixed location).
Of course you can't swim that well in long sleeved clothes hence the popularity of sunscreen. I'm totally against Aussie beaches at this point though, yes they are nice and all but the radiation dose is just nuts.
Would love to see something like the Apple Watch include UV dosimeter functionality.
"I’ve always felt sunscreen never lives up to its promise."
I agree with that for the same reasons. Nevertheless, I'll still use sunscreen when I have to. In Australia there are times when it's hard to avoid the sun but I avoid it at every opportunity.
If at the end of a day I feel my skin the slightest bit sore from exposure I know I've not been proactive enough.
Maybe it’s inconvenient, but for me the promise is sun protection, and for that it for sure works.
Spray goes on easier, not only does spray cover area, but it spreads easier than cream too, but anything is better than nothing. But I have drifted towards preferring long sleeves, hats, and even a sun umbrella so I don’t have to get greased up.
In Australia here. I tend to go morning or 3pm. Crowds reduce, UV is lower, sun goes down 8pm in summer (so 3-8 is 5 hours). Anything near midday is silly.
Hill country TX where 8 month out of the year are 35 C daily and way too much humidity.
Agreed, partially. There are times one has to do things when it's blazing hot.
On sunscreens, we're still missing:
- amiloxate
- bemotrizinol
- bisdisulizole disodium
- bisoctrizole
- drometrizole trisiloxane
- tris-biphenyl triazine
While continuing to allow:
- 4-MBC (enzacamene)
- avobenzone
- oxybenzone
- homosalate
- octinoxate
- octocrylene
In the US, buying a safe(r) (for humans and reefs) sunscreen requires a medical and a marine biology degree unless you're willing to slather yourself in white pastes like zinc oxide or titanium dioxide. One major barrier is the law demands animal testing prior to approval.
Meanwhile, there are still millions of Americans (mostly men) who routinely venture outdoors for work and projects without sufficient protection and accumulate enough exposure that leads to preventable skin cancer. And I had my fair share of sunburns as an active kid.
If a product can pass for years and then fail, the real problem is the trust gap. The fix is boring but workable: clear test methods, lot-level results, independent re-tests, and recalls when needed. Without that, consumers can’t tell good from bad.
Wait until you learn that some of the sunscreens sold (can't say specifically in Australia, but I know this is the case in the US) only block UVB, so you won't get a sunburn but you will still get exposed to unhealthy amounts of UVA. Basically sunscreen is often optimized to not make you burn, which burning might actually be a good thing since it's preventing you from getting exposed to even more UVA.
Took a quick look and apparently the issue is pretty widespread: https://www.ewg.org/sunscreen/report/whats-wrong-with-high-s...
I use sunscreen myself sometimes but using artificial methods gives me pause. Whenever possible I just wear a UV shirt and a hat instead.
Melanin is a real climatological adaptation. So are burqas.
So is intelligence according to some research. The colder it was, the more intelligent we became. We Europeans exchanged melanin for points in IQ?
http://dx.doi.org/10.1016/j.intell.2005.04.002
Note that I didn't look into this paper in detail. I just used searched for "cold climate high intelligence" and picked the first result after checking the abstract.
What is also awful was the number of "influencers" aka digital door-to-door salespersons pushing that Ultra Violette sun screen slop on TT and Insta.
There is no repercussions for these clowns pushing a faulty product into the masses. I guess they actually are the winners here because they walk away with cash while their followers end up with shitty product and the company has to deal with the fallout. I doubt the digital door-to-door salespersons reputation suffers as their audience will still lap up anything they sell like a thirsty dog in the desert.
> She says the scandal is a reminder that regulations are only as good as they are enforced.
I feel like we're going to be reminded of this a lot more in the coming years...
<Twiddles moustache> These expensive, job-killing regulations are nothing but bureaucratic red tape! Vote for me and we'll give you back your freedom!
(Why must this work?)
It’s hard to argue the answer here is more regulation.
It's been 44 years since the original Slip, Slop, Slap! PSA campaign was launched on Australian TV and billboards.
https://www.youtube.com/watch?v=b7nocIenCYg
Revised & updated in 2010: https://www.youtube.com/watch?v=FzA47J7QsVkand 90s versions like Me No Fry (https://www.youtube.com/watch?v=rsgdT8YYwJo)
How did they ever not do Blister in the Sun ?
Everyone in Australia gets skin cancer. It's just normal. My grandma had something like 5 or 10 of them removed. In general, kids these days spend less time outside and do understand the value of hats and sunscreen or long sleeves, so it's getting better. The face can be hard, particularly without a hat.
I always laugh when people wear those stupid baseball caps instead of proper hats with brims. They think it's 'cool'. Mate, the main person laughing at your 'cool' is future you - dying from skin cancer on your face.
"Mad dogs and Englishmen go out in the midday sun." - https://www.phrases.org.uk/meanings/mad-dogs-and-englishmen....
Stupid question since I don't live in Australia. Is the skin cancer a consequence of the sunburn or do they get it without sunburn?
I can't speak for Australia, but in general you definitely don't need to burn for increased cancer risk - a clear example of that is the fact that artificial UV tanning beds lead to significantly increased rates of cancer despite the fact that they're used in such a way that you tan without going far enough to burn.
Although we often think of burning as bad and tanning as good, tanning is nonetheless still actually a symptom of your skin being damaged by the sun - it's just a symptom that looks better than burned skin, to the point that many people think it looks nice enough to be worth the cancer risk (and/or don't understand the risk when they decide to tan).
Why is it particularly bad in Australia? Is it simply that it's the whitest country at that kind of latitude?
Summer in Australia gets more power from sun than summer in e.g. France, because of the elliptic trajectory of earth. ~ 7% more.
They get the worst of the "hole" in the ozone layer.
Kalahari hats are my go-to when outside these days.
https://www.sunsafeaustralia.com.au/headwear/p/uveto-austral...
I wear a baseball cap and a hooded sun shirt. Plus mineral sunscreen all over my face and neck.
https://hendersonvilleoutfitters.com/products/upf-shirts
Technically both of these approaches are not as good as a wide brimmed hat in terms of face protection. However, for some sports it's superior (anything with wind or clearance issues). I'm on a Stetson at the moment after a US trip but usually go for whatever broad brim is available. Buying new ones gets old so going for a 'crushable' model is the go - I like the felt Stetsons. The other benefit from a broad brim is it functions as an auto-umbrella in light weather which is damn cool. Also, hat-on-face is similar to those plane-sleep-eyewear bands.
Yeah, I wouldn't classify it as a hat anymore. Looks more like a hoodie.
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