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/
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