7 Dangerous Sunscreen Mistakes Not to Make This Summer

There are two different kinds of UV rays attacking your skin. "UVA rays can prematurely age your skin, causing wrinkles and age spots and can pass through window glass," says Mayoral. "UVB rays are the primary cause of sunburn and play a key role in the development of skin cancer; they're the one that are more prevalent between 10 a.m. and 4 p.m."

But overexposure to either can lead to skin cancer, so you want to make sure you choose an SPF (30, at the very least) that can protect you from both; those have the word broad-spectrum on them.