Im confused about if it is effective once absorbed or if it literally creates a “screen” on your skin
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There are two main categories of sunscreen ingredients: physical and chemical.
Physical sunscreen ingredients (like the white titanium dioxide you stereotypically see on peoples noses in movies) blocks or scatters the radiation from the sun. These typically sit on top of the skin and simply stop some radiation from reaching your skin.
Chemical sunscreen ingredients absorb the radiation from the sun. These are typically absorbed into the skin.
Some sunscreens use only physical ingredients, some use only chemical, and some use both.
Sunscreen is only effective while it is on/in your skin (not washed off) and hasn’t worn out. Some sunscreens are water resistant and some are not. The time they will last may depend on things like the ingredients, how much you’re perspiring, if you’re in water and if the sunscreen is water resistent, and how much sun there is.
You should read the instructions for the particular sunscreen before you use it.
https://www.skincancer.org/skin-cancer-prevention/sun-protection/sunscreen/
It works by absorbing/scattering most of the UV light before it reaches your skin and causing cancer. If it’s “absorbed” it makes it harder to be removed and therefore lasts longer.
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I think it is important to note that reading the “how was this rating calculated” section of the sunscreen companies website is usually ***really*** informative.
All the sunscreens I’ve read that section for stated that they used 1/4 cup of sunscreen to achieve that level of protection…. Which is way more than most people put on per application.
UV is an extremely high energy wave. Counter intuitively, high energy waves are bad at piercing through matter. This is why radio waves (long, low energy waves) can be heard through concrete while 5g can’t enter most houses.
UV damages your skin at the surface, and a very thin layer of material will block most of the effects of UV for the reasons mentioned above.
Basically, it is paint that is transparent for visible light, but black or white for UV light. So whe we look at a painted surface, photons scatter off or get absorbed by the paint, same happens with sunscreen and your skin: uv light is absorbed by or scattered by sunscreen layer instead of the skin
Sunscreen is not absorbed, [it’s just a paint which is dark in UV part of the spectrum, and transparent in the visible one](https://www.youtube.com/watch?v=yrs3_F5uzJI), so it sits on top of your skin, absorbs UV rays while allowing most of visible light to pass, and converts UV into heat. Just like dark paint on the sun absorbs light and heats up. Mineral sunscreen also reflects a couple of percent of light, but not all contrary to what other users might have have said, it’s an old myth.
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