Frequent Application of Sunscreen Essential to Avoid Sunburns

NEW YORK-Many persons who apply sunscreen before spending time outdoors are nevertheless increasing their risk of skin cancer by not applying sunscreen frequently enough to prevent sunburn, recent studies involving skiers at high altitudes suggest.

"Unfortunately, we know that it’s behavioral differences that make a difference in melanoma," said Darrell S. Rigel, MD, clinical professor of dermatology, New York University. "People get up in the morning, put the sunscreen on once, and forget to reapply. Later in the day, they pay for it with a sunburn."

Dr. Rigel, speaking at an American Academy of Dermatology (AAD) press conference, described several studies conducted this past winter at a high-altitude ultraviolet radiation research center in Vail, Colorado, where a person can sunburn within 10 minutes at peak times of the year. "Altitude makes a big difference, and provides us with a good area to test the effectiveness of sunscreens," Dr. Rigel said.

To determine factors influencing effectiveness of sunscreen at these heights (8,000 to 11,000 feet), Dr. Rigel and his colleagues randomized 105 people skiing for a week in Vail to sun protection factor (SPF) 15 or SPF 30 sunscreen. "We were fortunate to have seven perfectly beautiful, cloudless days," he said.

Investigators assumed it would be the SPF of the sunscreen that would make a difference in whether people burned or not. However, there was no difference in reported sunburn incidence for SPF 15 vs SPF 30 by total exposure days, total exposure hours, average exposure hours, or average applications per day.

The only significant predictor of sunscreen failure was how frequently people applied the sunscreen. Only 2% of participants who applied sunscreen every 2 hours or more often were sunburned. Sunburns were fivefold more common (10% incidence) among people who applied sunscreen every 2.5 hours or less frequently.

Ski Instructors Study

In a related study, investigators gave 10 ski instructors personal digital ultraviolet light detectors to be fastened to their wrists and forearms. A total of 84 exposure days for ultraviolet B (UVB) and 66 days for ultraviolet A (UVA) were measured.

Average daily exposure to UVB was 62.1 mJ/cm², or nearly three times the minimal erythema dose (MED) for persons with skin type II (20 to 25 mJ/cm²). Average daily UVA exposure was 10.6 mJ/cm².

At peak midday hours, participants’ dosimeters registered 2.5 times skin type II MED in 1 hour. "This was actually done during December, when the sun would be the weakest," Dr. Rigel noted.

Taken together, these findings reinforce AAD recommendations that a sunscreen with an SPF of 15 or greater should be used and regularly re-applied, at least once every 2 hours, for maximal efficacy.

"Prevention is still the key to combating this deadly disease," said Roger I. Ceilley, MD, co-chair of the AAD’s communications council. "By wearing a broad-spectrum sunscreen of at least SPF 15, using sun-protective clothing, a broad-brimmed hat, and avoiding the midday sun, we can do our best do prevent skin cancer, and prevent skin cancer developing in our children."

Dr. Rigel added that sunscreen should be integrated into a complete sun protection regimen. "I think things like that, used in combination, will make sunscreens more effective and hopefully, in the long run, will lower some of those melanoma statistics."