Uva Vs. Uvb: What's The Difference?
The goal of any sunscreen is to provide protection from the sun's UV rays. But there are different types of rays, and it's important to know the kind of damage each one can cause.
UVB rays have shorter wavelengths and are primarily responsible for skin cancer and sunburns, which is why they're called "burning rays." SPF refers to a sunscreen's ability to protect against UVB rays, which cannot penetrate window glass.
UVA rays, or "aging rays," have longer wavelengths that can penetrate deeper into the skin, leading many dermatologists to believe they cause more harm than UVB rays. Premature aging and skin cancer can be a result of long-term exposure to UVA rays, which are used in tanning beds and can penetrate window glass. This is why it's very important to wear a UVA-blocking sunscreen at all times.
There is currently no rating system for UVA rays; however, look for sunscreens that say "broad-spectrum" on the label, because they contain active ingredients that help shield skin from both types of rays.