1. “SPF” stands for “Sun Protection Factor.” The higher the SPF number, the more protected you are from UVB rays (the ones that burn your skin). Note: UVB protection doesn’t increase proportionately as SPF goes up. The biggest leap comes between SPF 15—which blocks 93 percent of UVB rays—and SPF 30, which blocks 97 percent.
2. "Sunblock" contains particles that block UV rays. "Sunscreen" is made of chemical components to absorb UV rays.
3. “Broad spectrum” means that a product guards against UVA rays (which cause signs of aging) and UVB rays (responsible for sunburn). The importance of applying broad spectrum SPF extends to your everyday moisturizer.
4. “Water resistance” tells you that a lotion will stay on your skin longer through sweating or swimming. However, no sunscreen is waterproof—you still have to re-apply when you get out of the water.
5. "Active Ingredients": The FDA recognizes 17 active ingredients that offer sun protection, but some are certainly more effective than others, and research points to potential dangers associated with some that are approved. The most effective ones are absorbers like Parsol 1789 (avobenzone) and Ecamsule (mexoryl), which soak up rays from the sun, and reflectors like titanium dioxide and zinc oxide, which sit on the surface of the skin and deflect rays. Oxybenzone, on the other hand, is approved by the FDA, but it can irritate skin, and some research has linked it to increased cancer risk.