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What's in a Number? What SPF Really Means


When it comes to sunscreen, it is logical for someone to think that an SPF of 50 or 75is better than an SPF of 15 and so on. But that is not exactly how it works.

Most dermatologists and other physicians will tell you, if you are using anything above an SPF 30, you are just adding more unnecessary chemicals to your (or your children’s) skin and wasting money as higher SPF sunscreens are usually more expensive.

SPF refers to the ability of a sunscreen to protect against ultraviolet B (UVB) rays that cause sunburns, but not UVA rays, which are more closely linked to deeper skin damage. Both UVA and UVB contribute to the risk of skin cancer.

The SPF rating is a measure of the time it would take you to sunburn if you were not wearing sunscreen as opposed to the time it would take with sunscreen on.

An SPF 15 product blocks about 94 percent of UVB rays; an SPF 30 product blocks 97 percent of UVB rays.

After that, it really does not matter as the difference in sunburn protection between the medium- and high-SPF sunscreens is minimal. 

“The best sunscreens are SPF 30 or higher, broad spectrum and water-resistant. Broad spectrum indicates that the product protects against both UVA and UVB,” says Dr. Chesahna Kindred, a dermatologist in Baltimore, Md.

Dermatologists suggest that rather than focusing on the SPF number, it's more important to choose a broad spectrum sunscreen (one that protects against both UVB and UVA rays), and to focus on wearing enough.

Dr. Kindred says that one ounce of sunscreen, enough to fill a shot glass (or the size of a golf ball), is the amount needed to cover the exposed areas of the body. “Also, do not forget to apply to the ears and parts in scalp. It takes about 15 minutes for the skin to absorb the sunscreen, so apply before going outdoors. Reapply every two hours and immediately after swimming or excessive sweating,” adds Dr. Kindred.

If you are applying correctly, SPF 30 should be all you need.

Written by Cristi Driver


August 31, 2015 by Blue Lizard Staff
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