The truth about SPF: Is there a magic number?

Posted at 12:09 PM, Jun 06, 2016
and last updated 2016-06-06 12:24:20-04

When it comes to choosing the right sunscreen, understanding all the acronyms — SPF, UVA, UVB — and whether there is a magic number can mean the difference between a pleasant sunny day, a painful sunburn, or worse — skin cancer.

Many people are unsure what SPF means, other than a higher number is better. SPF stands for Sun Protection Factor, and it explains how much protection you’ll get from certain types of the sun’s ultraviolet radiation.

To help you choose the best sunscreen, consider these important aspects.

Why you should wear sunscreen

At the most basic level, sunscreen protects your skin from the sun, helping to prevent skin cancer. This is the most common type of cancer, and according to the American Cancer Society, skin cancer is largely preventable.

“There are more than 5 million skin cancer cases that are diagnosed annually and many could be prevented by protecting skin from excessive sun exposure and not using indoor tanning devices,” the ACS says.

Beyond cancer, protecting your skin from the sun will prevent painful sunburns that make it difficult to function. Sunburns can increase the risk of skin damage, including wrinkles, spots and even melanoma.

The difference between UVA and UVB rays

Ultraviolet radiation, in the form of UVA and UVB rays, is sunlight that penetrates the atmosphere and damages your skin, eyes and immune system, according to the Skin Cancer Foundation.

UVA rays are less intense but more common than UVB rays. Despite changing temperatures, UVA rays are about the same intensity throughout the year and can penetrate clouds and glass.

“UVA is the dominant tanning ray, and we now know that tanning, whether outdoors or in a salon, causes cumulative damage over time,” the SCS says. “A tan results from injury to the skin's DNA; the skin darkens in an imperfect attempt to prevent further DNA damage. These imperfections, or mutations, can lead to skin cancer.”

UVB rays are the major cause of sunburns and have varying levels of intensity throughout the day and year, and in different locations. They do not penetrate glass, but “UVB rays can burn and damage your skin year-round, especially at high altitudes and on reflective surfaces such as snow or ice, which bounce back up to 80 percent of the rays so that they hit the skin twice,” the SCS says.

What SPF means

SPF refers to protection from UVB rays, the primary cause of sunburns.

“When applying an SPF 30 sunscreen correctly, you get the equivalent of 1 minute of UVB rays for each 30 minutes you spend in the sun,” says the American Cancer Society.

The ACS recommends using sunscreen with broad-spectrum protections, which means it protects against both UVA and UVB rays. It encourages people to use at least SPF 30 and says anything below SPF 15 does not protect against skin cancer or early skin aging.



Proper application

SPF doesn’t matter if sunscreen is applied improperly. The American Academy of Dermatology advises generously applying sunscreen at least 15 minutes in advance to give your skin time to absorb it, otherwise, you will not be protected.

Adults generally need at least one ounce of sunscreen, “about the amount you can hold in your palm,” the AAD says, and should reapply every two hours or immediately after swimming or sweating excessively.

“People who get sunburned usually didn't use enough sunscreen, didn't reapply it after being in the sun, or used an expired product,” the AAD says. “Your skin is exposed to the sun's harmful UV rays every time you go outside, even on cloudy days and in the winter. So whether you are on vacation or taking a brisk fall walk in your neighborhood, remember to use sunscreen.”

So, what is the magic number?

It’s up to you. While SPF 30 is the lowest recommended number, you may choose to go higher when spending more time in the sun. One thing experts agree upon is people should protect themselves from the sun every day, not just in summer.