Some sunscreens protect against only UVB rays, which are the primary cause of sunburn, but UVA rays penetrate deeper into your skin. Both UVB and UVA exposure can lead to premature skin aging, skin cancer, and sunburn.
Only sunscreens labeled as both "Broad Spectrum" and "SPF 15" (or higher) can reduce the risk of skin cancer, and reduce the risk of early skin aging -- if they’re used regularly, as directed, and in combination with other sun protection measures that will help prevent sunburn. (The SPF – sun protection factor -- rating refers only to the level of protection from UVB rays, not UVA rays.)