Around my office, I’m the sunscreen nut. I never leave the house without it, and given the chance, I’ll lecture anyone about the importance of vigilant reapplication. Sunscreen’s come a long way from the purple goo I smeared on my face as a kid, and new ingredients and formulas are making them more comfortable, longer-lasting, and much more enticing to use.
Putting on sunscreen is like applying an invisible supernatural force field. Summer may be the season when people’s thoughts turn to sunscreen, but rarely do we think about exactly how it works. It may seem like magic, but it’s science that makes sunscreen work.
The UV Alphabet
Skin is harmed by two different kinds of ultraviolet light—UV-A rays and UV-B rays. UV-A rays have the longest wavelength, and they penetrate deepest into our skin, causing premature aging and increasing our cancer risk. UV-B rays have a shorter wavelength, and although our atmosphere absorbs many of these rays, the ones that make it to earth cause sunburn. The sun also generates UV-C rays, but the atmosphere completely blocks these and they never make it to earth. The American Academy of Dermatology recommends this clever way to remember the UVs—UV-A rays cause aging, while UV-B rays cause burns.
Sun protection products work by either absorbing or reflecting away the harmful UV rays. There are two kinds of sun protection—chemical barriers and physical barriers. Chemical barriers soak into the skin like lotions, and the molecules in them absorb UV rays and release them as heat before they can do any damage. On the other hand, physical barriers sit on the surface of the skin, like the chalky, white zinc oxide used on the noses of lifeguards. It’s like covering your body in a thin mirror. Even though many people use the terms sunscreen and sunblock interchangeably, they are actually two different products. A sunblock must have an SPF of twelve or higher and contain a physical barrier, while sunscreens can be any product with an SPF of two or higher. Even a plain white tee-shirt has an SPF of about three. Since they are easier and more comfortable to use, most products we use today are sunscreens.
