How does sunscreen actually work?

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How does sunscreen actually work?

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Black paint absorbs all visible light.

Red paint absorbs most or all green light.

What if we had a paint that absorbs UV light? It could be totally transparent to visible light, but block UV before it hurt your skin. That would be sunscreen.

Sunscreen is a colour of paint or pigment that absorbs UV light, rather than absorbing visible light like regular paints do. By absorbing the UV light right there at the skin’s surface, it prevents the UV light from striking the skin itself and causing sunburn damage.

Basically, it blocks your skin from UV light the same as painting yourself with black paint would block visible light from hitting your skin.

To prove this, look at [what sunscreen looks like under UV light](https://twitter.com/skinhealth_inst/status/1057029457238732800). It looks like black paint! [You can draw with it.](https://www.youtube.com/watch?v=YUY3EM4PtaI)

There are [2 kinds](https://images.app.goo.gl/SYb28SdCdjN8UgQs5), sometimes called “chemical” and “physical” sunscreen. I think chemical is more common these days, because it works more fully, and is more waterproof.

Chemical sunscreen uses several ingredients that absorb UV radiation and convert it to heat, so that your skin doesn’t have to receive it and be damaged. Usually it can be absorbed into your skin as a lotion, which helps it to not get washed off.

Physical sunscreens contain zinc oxide and/or titanium dioxide, which reflect UV radiation instead of absorbing it, so it’s more like painting a mirror on your skin. These types of sunblock are harder to make quite so effective, so they can’t be as high SPF, and they don’t get absorbed by the skin so they’re easier to wash off if swimming or sweating.

Notably, the feeling is quite different between the 2 types. With physical sunscreen, which is what I was used to in my childhood, you sort of “can’t feel” the sun on you. It doesn’t feel warm in direct sunlight because so much is being reflected. You could apply this kind of sunscreen to one part of yourself, and leave another part with no sunscreen, and go into direct sunlight, and you can easily tell the difference.

Whereas chemical sunscreen doesn’t feel that different from being in the sun unscreened. (It will probably feel better if you’re already burned though.) Since it gets absorbed into your skin and doesn’t reflect UV radiation, you still feel the sun on you, and the sunscreen absorbs the rays and releases heat, so you still feel the warmth too.

Two types;

1. Chemical – converts the UV rays into heat energy via chemical reactions
2. Physical – blocks UV rays reaching the skin. e.g zinc