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Comment by mitthrowaway2 | Hacker News Reader

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!

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> 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.

> 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).

"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)

> They don't always say that

We're talking about chemical sunscreens here, and they should say it because they do require it.

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.

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