How does sunscreen protect your skin from UV radiation?



More specifically, does spf sunscreen work by reflecting UV or absorbing it?

I always assumed it reflected UV waves away from the body to protect the skin underneath, but then I see those “UV camera” photos where the sunscreen shows up dark which I was taught (if I remember correctly) means the sunscreen is absorbing all the UV and therefore not showing up on the image (no light being bounced into the lens). If it is being absorbed, does it disparate the energy somehow to stop it from harming the skin cells underneath? This has been bugging me for quite some time. Please help.

In: Physics

not quite eli5 but Chemical **sunscreens** contain organic compounds that catalyze a chemical reaction when exposed to the sun; this reactions transforms **UV** rays into **heat**,


Physical sunscreens like zinc and titanium dioxide form a physical barrier and reflect the UV rays away from the skin.

Chemical sunscreens such as avobenzone, octinoxate and oxybenzone go into the skin and absorb the UV rays and converts into heat.

I don’t think this fully answers your question but hopefully someone else can chime in and answer what happens after it is absorbed

There are two types of sunscreen: chemical (that works like quietoldsoul is saying) and mechanical, that physically blocks of the uv from hitting your sun. If you search for physics girl on YouTube she has an episode where she explores different types of sunscreen/sunblock in a UV-camera – I’m sure you will enjoy it although she’s probably more eli14.

Edit: [here](

I think it might help to understand what colors and how we see them when there is light on it.

Light from the sun basically has ALL the colors. When we see something of a certain color such as a red shirt, it actually mean that our eyes receive red light. But the shirt isn’t emitting light. So how come we see red? Simply because the dye used on the shirt ABSORB the other colors (usually turning them into heat). So that red shirt is red because all other colors are absorbed. Which also explain why shining a green light on a red shirt (like in a discotheque) lead to the shirt showing black: it has no red light to refract. It’s also why dark clothes usually keep you warmer, they absorb most color and turn them into heat.

Now, what are UV? Ultra Violet is a form of light. It just happens that our eyes are not capable of perceiving it. But they act pretty much like all other lights. Which mean, that with the proper dye, you can absorb it. That’s what sunscreen can be summarized as. A dye of an invisible color (basically, that doesn’t reflect any color our eye is capable of seeing) that absorb UV.