Probing Question: What does the SPF rating of sunscreen mean?

June 4, 2010 By Chris Tachibana
Probing Question: What does the SPF rating of sunscreen mean?

"Tanned skin is damaged skin." That's the dire message from the Centers for Disease Control (CDC). We need a little sun exposure for vitamin D production, but too much sun increases the risk of skin cancer.

So, if we want to safely spend time in the garden and the pool, we need to first spend time in the aisle of the drugstore. Waterproof, sweatproof, UVA, UVB, SPF 15, 50, or 100…what does it all mean?

SPF stands for sun protection factor, but it specifically indicates protection against the ultraviolet B (UVB) rays that cause sunburn, said Kimberly Mallett, research associate in the Penn State Prevention Research Center. "Imagine that your skin normally begins to burn after 10 minutes in full sun without any protection. A 30 SPF sunscreen would provide 30 times the protection of no sunscreen."

That means 30 times longer before you start to burn, or in this case, 300 minutes. That's five hours, so one application should do it for the day, right? Not so fast, said Mallett. She recommends reapplying sunscreen "every one to two hours when outdoors, especially if swimming or sweating a lot. Even if the sunscreen has a SPF of 100, claims to be sweatproof and waterproof, and provides all-day protection, it needs to be reapplied to provide optimal protection."

An SPF of 100 does not mean twice the protection of SPF 50, Mallett added. Even an SPF 15 sunscreen blocks over 90 percent of UVB rays, so you don't need an SPF of 80 or 100 for adequate protection. Proper and repeated application is more important. Still, "Reapplying sunscreen does not start the clock over," said Mallett. More sunscreen just replaces what has worn off, rather than adding on more hours of protection. And Mallett warns that redheads and blondes might want to be extra careful. "The SPF numbers are not exact, and results vary by individual, since some skin types burn faster than others."

Another factor to consider is protection from UVA rays. These might not cause a visible sunburn, but they can still damage tissue and cause wrinkles, and they penetrate deeper into the skin than UVB rays.

The CDC says that UV rays cause 60-90 percent of melanomas, the most dangerous type of skin cancer. Yet in spite of public health warnings, two-thirds of people between 15 and 29 admit to getting at least one serious sunburn in the previous summer, according to a survey from the Danish Cancer Society. Millions of people use tanning beds every year, even though the CDC says their UV rays are just as dangerous as UV from the sun. To help get the message out about how to reduce risk, Mallett is currently working on a project funded by the National Cancer Institute to train Penn State dermatologists to motivate patients to use sunscreen and other protection against UV rays.

Once you're convinced that your skin is worth protecting, Mallett recommended "a broad-spectrum, water-resistant sunscreen that protects against both UVA and UVB rays with a minimum SPF of 30." Then, she advised, "Apply sunscreen liberally and thoroughly, at least 30 minutes before going out so that it has time to absorb into the skin, and don't miss sensitive spots like the ears and feet."

Finally, remember that sunscreen can do only so much, and a big umbrella and some stylish beachwear might be your best bet. "Seek shade, and wear hats and clothing if out in direct sun for prolonged periods of time," said Mallett. Add a pair of sunglasses (they look cool and can reduce the risk of cataracts), and you're ready for the long, sunny days of summer.

Related Stories

Recommended for you

Brain disease seen in most football players in large report

July 25, 2017
Research on 202 former football players found evidence of a brain disease linked to repeated head blows in nearly all of them, from athletes in the National Football League, college and even high school.

Safety of medical devices not often evaluated by sex, age, or race

July 25, 2017
Researchers at Yale and the University of California-San Francisco have found that few medical devices are analyzed to consider the influence of their users' sex, age, or race on safety and effectiveness.

Why you should consider more than looks when choosing a fitness tracker

July 25, 2017
A UNSW study of five popular physical activity monitors, including Fitbit and Jawbone models, has found their accuracy differs with the speed of activity, and where they are worn.

Dog walking could be key to ensuring activity in later life

July 24, 2017
A new study has shown that regularly walking a dog boosts levels of physical activity in older people, especially during the winter.

Study finds 275,000 calls to poison control centers for dietary supplement exposures from 2000 through 2012

July 24, 2017
U.S. Poison Control Centers receive a call every 24 minutes, on average, regarding dietary supplement exposures, according to a new study from the Center for Injury Research and Policy and the Central Ohio Poison Center, ...

Alcohol to claim 63,000 lives over next five years, experts warn

July 24, 2017
Alcohol consumption will cause 63,000 deaths in England over the next five years – the equivalent of 35 deaths a day – according to a new report from the University of Sheffield Alcohol Research Group.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.