Sunscreen 101

Deciphering SPF: What You Need To Know To Stay Sun Safe

June 16, 2018

Many skin care products tout SPF on the packaging, but what does that mean exactly for your skin?

There are many types of light that impact our skin. Two types of rays coming from the sun are Ultraviolet A (UVA) and Ultraviolet B (UVB). UVA is a longer wavelength and is tied to causing skin damage such as aging and certain types of skin cancer. UVB is a shorter wavelength that causes skin damage such as sunburn and certain types of skin cancer. The term SPF stands for “Sun Protection Factor” and was introduced in 1974.

Unfortunately, this measure of a sunscreen’s efficacy only calculates how well the sunscreen works to protect against UVB alone. In 2012, the final sunscreen rules by the U.S. Food and Drug Administration (FDA) defined the term “broad-spectrum” as providing proportional UVA and UVB protection.

The Number War

Many sunscreen companies seem to be fighting an ongoing battle to determine who can list the highest SPF. So, what is the difference between SPF 30, SPF 50 and SPF 100?

“SPF 30 reflects 96.7% of UVB, SPF 50 reflects 98% and SPF 100 reflects 99%,” says Dr. Carl Thornfeldt, clinical dermatologist and founder of Epionce skin care. However, he added, “a microscopic evaluation of damaged sunburn cells showed there were 78% fewer damaged sunburn cells with SPF 50 than with SPF 30.”

This is why many physicians are starting to recommend an SPF of at least 50. The difference between the SPF 50 and SPF 100, though, is negligible. The biggest problem, Dr. Thornfeldt notes, is that, “…the average amount of sunscreen applied is 25-40% of the amount recommended by the FDA.” This is important because sunscreen protection drops exponentially, so if one uses 50% of the amount of an SPF 70 as recommended, the protection is only SPF 8.4.

“A full ounce,” the American Academy of Dermatology recommends, “is needed to fully cover all exposed areas of the body.”

The other major application issue dermatologists see is “substantively”—which is the measure of how well sunscreen binds to the skin. If a sunscreen is not marked as “water-resistant” or “very water-resistant,” it will sweat off in 10-30 minutes.