Know the Lingo
The sun has three kinds of ultraviolet rays with different wavelengths.
UVA leads to skin aging and cancer
UVB causes burning and cancer
UVC can't pass through the ozone layer
In the past, experts believed that UVA -- which accounts for up to 95 percent of all UV radiation that reaches the earth -- caused fewer cancerous mutations than UVB. But new research shows that UVA, which penetrates deep into the lower levels of skin, may actually be equally dangerous.
1. A sunscreen's SPF (sun-protection factor) is a measurement of how well it protects against sunburn. If you slather on an SPF 30 product, you should be able to stay in the sun for 30 times longer without burning than if your skin were bare. However, SPF only measures how well a sunscreen blocks UVB. There are no numbers that measure protection against UVA.
2. Clothing's UPF (ultraviolet-protection factor) reflects how much total UV the fabric blocks. UPF 50 means that only one-fiftieth of all UV rays (2 percent) can shine through.