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You’re kidding? You want millions of people to apply something that gets absorbed into the skin without testing it for side effects?

mcbain 1y ago
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.
mitthrowaway2 1y ago
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!
- chimeracoder 1y ago
  > 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.
  - jiggawatts 1y ago
    > 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.
    - chimeracoder 1y ago
      > More importantly, it is cheap enough to be always used as a baseline verification > It's like unit testing vs full user acceptance testing. You can and should do both, but the latter isn't for every PR. You say all this as if it weren't already happening. OP was surprised human testing was being conducted at all, not that non-human testing wasn't being done (which is a claim nobody made, and which isn't true).
  - lukan 1y ago
    "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)
    - chimeracoder 1y ago
      > They don't always say that We're talking about chemical sunscreens here, and they should say it because they do require it.
- casey2 1y ago
  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.
shermozle 1y ago
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.
- pmontra 1y ago
  How did they measure the effectiveness of the sunscreen and any side effects on your skin?
- wkat4242 1y ago
  You get paid for an hour in the jacuzzi? Sign me up ;)
SapporoChris 1y ago
You're kidding? You equate "not testing on human subject" to "not testing"?
dzhiurgis 1y ago
Skin doesn’t just absorb things. In fact it’s incredibly good at resisting so much so that most beauty products are complete BS.
- johnisgood 1y ago
  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.

mcbain 1y ago

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.

mitthrowaway2 1y ago

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!

chimeracoder 1y ago
> 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.
- jiggawatts 1y ago
  > 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.
  - chimeracoder 1y ago
    > More importantly, it is cheap enough to be always used as a baseline verification > It's like unit testing vs full user acceptance testing. You can and should do both, but the latter isn't for every PR. You say all this as if it weren't already happening. OP was surprised human testing was being conducted at all, not that non-human testing wasn't being done (which is a claim nobody made, and which isn't true).
- lukan 1y ago
  "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)
  - chimeracoder 1y ago
    > They don't always say that We're talking about chemical sunscreens here, and they should say it because they do require it.
casey2 1y ago
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.

shermozle 1y ago

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.

pmontra 1y ago
How did they measure the effectiveness of the sunscreen and any side effects on your skin?
wkat4242 1y ago
You get paid for an hour in the jacuzzi? Sign me up ;)

SapporoChris 1y ago

You're kidding? You equate "not testing on human subject" to "not testing"?

dzhiurgis 1y ago

Skin doesn’t just absorb things. In fact it’s incredibly good at resisting so much so that most beauty products are complete BS.

johnisgood 1y ago
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.