Sunscreen explained, demystified
Tribune staff writer
For many years, sun protection factor 15 was the highest sun block ointment available, unless you wanted to slather yourself in solid white zinc oxide and look like someone from the moon.
Then, it went up to SPF 30, then 50. Just when you thought it couldn’t go higher, there are now suncreens for sale in SPF 70.
But according to the American Academy of Dermatology, SPF protection does not increase proportionately with a designated SPF number.
“That’s the key. People think SPF 60 is twice as good as SPF 30. It’s only slightly better,” said Dr. Dianne Kamenetsky, a dermatologist who practices in Truckee.
Here’s the breakdown: SPF 2 absorbs 50 percent of the sun’s rays, SPF 15 absorbs 93 percent and SPF 30 absorbs 97 percent of sunburning rays. Type B ultraviolet rays, otherwise known as UVB, cause sunburns.
Kamenetsky still recommends higher SPF ratings, 30 or above, because people don’t spread it on enough.
“When they measure the SPF it’s in a lab. They put a small amount on a layer of skin, and they determine the SPF by how much redness appears,” Kamenetsky explained.
“But when you do it in real life, no one puts it on as thickly and evenly, it migrates on the skin, so a higher SPF can still be more effective,” she said.
It is recommended that a teaspoon’s amount should be used on the face, and shot glass full or so for the body.
SPF multiplies the amount of time you can spend in the sun before burning. Each individual is different. A fair-skinned person who burns in 10 minutes would take 15 times longer to burn wearing SPF 15 sunscreen, or 2.5 hours. But someone who takes two hours to burn could get all-day protection from an SPF 15 sunscreen.
The SPF rating only applies to UVB rays. The AAD recommends looking for a sunscreen which blocks both types of ultraviolet rays: ultraviolet type A and B. While UVB rays cause sunburn and skin cancer, UVA rays penetrate deeper into the skin and cause wrinkles and possibly melanoma, the most deadly type of skin cancer. And, UVA rays can pass through glass.
Titanium dioxide and zinc oxide are the only ingredients which actually block sunlight, and they block both UVA and UVB rays. They are called physical sunscreens.
“Zinc is best because it is not absorbed into the skin. They have really nice formulas with zinc oxide nowadays which are not solid white,” Kamenetsky said.
Chemical sunscreen ingredients, on the other hand, do not block but absorb light. Each type of chemical absorbs either UVA or UVB rays, but not both. Chemical sunscreens are absorbed into the skin, and have been found in urine. Because of this, it is not recommended that chemical sunscreens be used on infants younger than six months, Kamenetsky said.
Sunscreen users may want to think again before spending twice the price for SPF 70. The FDA may soon get rid of SPF ratings above 30, Kamenetsky said.
“They are only going to be able to say SPF 30 plus, because it’s kind of misleading to the public,” she said.
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