# How do sunscreens protect the skin from UV rays?

I was unsure to the largest extent about whether I should post this question in chemistry Q & A or bio Q & A until I just read that sunscreens "absorb" UV rays, not allowing the most of those rays from penetrating into the skin. So when this is about the combination, it must be chemistry.
Anyhow, is there any special name for these "absorbents"? And how exactly, do they "absorb" UVA & UVB? (I'm not really definite if this absorbing is really a scientific expression or not, and that's why I use quotations when using the word)
I, myself, reckon that the sunscreen products form a special compound on the skin or they make the body produce something as a shield against UV rays, but I have got no clues.

Apart from titanium dioxide, the active species in sunscreens are organic compounds from different substance classes, such as cinnamates, benzophenones, benzimidazoles, and triazines.

The do absorb in the 280-315 (UVB) and/or 315-380 nm (UVA) range. This "uptake" of energy results in an electronic excitation, the compounds undergo a transition from the $S_0$ (ground) state to an excited $S_1$ state.

The excited singlet state ($S_1)$ may

• deactivate radiationless via internal conversion (IC), the energy of the photon is released as heat or

• undergo intersystem crossing (ISC) to a triplet state (usually $T_1)$ with different spin multiplicity

The latter state then might again loose its energy via IC or undergo a chemical transformation, through which the suncreen might be turned to a species that not longer is able to absorb UV radiation.

Just to add, Zinc (like Titanium) is another UV filter that reflects UV light rather than absorbing it. I believe ever other UV filter, at least those approved in the U.S., absorb the UV rays.