A Answers (3)
The SPF number indicates the amount of sun exposure needed to cause sunburn on skin protected with sunscreen compared with skin not protected with sunscreen. A higher SPF value will offer more protection than a lower SPF value. For example, an SPF of 30 means it would take a person 30 times longer to burn when wearing sunscreen than the person would without sunscreen.
Not necessarily. Sunscreens with high SPF (sun protection factor) should provide more protection from the sun's ultraviolet (UV) radiation, which is a primary cause of skin cancers. But how well you apply the sunscreen and how often is nearly as important. Read instructions carefully and, in most cases, you need to reapply after going for a swim.
That said, the higher the SPF the better – until a certain point. For example, an SPF 15 sunscreen blocks 93 percent of UVB (ultraviolet B shortwave rays) – the chief cause of skin reddening and sunburn. Meanwhile, an SPF 30 sunscreen blocks nearly 97 percent. But the advantage of sunscreens above SPF 50, which blocks about 98 percent of UVB rays is questionable.
Ellen Marmur, MD, Dermatology, answered
When it comes to the SPF level in sunscreen, a higher number doesn't always mean better protection. In this video dermatologist Dr. Ellen Marmur explains why.