This article originally appeared in the San Francisco Chronicle on May 14, 2014.
It’s nearing high season for sunscreen. But before you run out to purchase some or slather on what’s left from last summer, here are five things to keep in mind.
On every label is SPF, which stands for sun protection factor. It tells us how well the sunscreen will filter out the sun’s ultraviolet radiation, which damages and ages skin and increases the risk of skin cancer.
Doubling SPF doesn’t double protection. An SPF 15 sunscreen, for example, filters out approximately 93 percent of all UVB rays. SPF 30 protects against 97 percent of UVB rays, and SPF 50 gets to 98 percent. The Food and Drug Administration recommends sunscreen no lower than SPF 15 and says there’s not much benefit in going higher than SPF 50.
Sunscreens have an expiration date. They can last up to three years, according to the Mayo Clinic. Check for an expiration date or write the purchase date on the bottle so that you know when you pull it out of your beach bag in three years, it won’t work.
Infants shouldn’t wear sunscreen. The FDA warns that chemicals in sunscreen could be harmful to babies younger than 6 months, so it’s best to keep them in the shade and protect them with hats and clothing.
Sunscreen spray can be flammable. Although rare, the FDA has received a few reports of people suffering burns while wearing spray sunscreen near open flames in barbecues, candles or cigarettes. Alcohol and other chemicals in the spray can catch fire, so read the label for warnings and use caution around flames.
There’s no such thing as “waterproof” or “sweat proof.” Starting in late 2012, the FDA outlawed these terms on sunscreen packaging, opting for “water resistant” instead. Labels must say how long the product will resist water or sweat before it’s time to reapply – either 40 or 80 minutes.