NAPA, CALIF. – When counseling patients to use sunscreens, instructions should also be given on how much to use, recommended Dr. Vincent DeLeo.
Sunscreens should prevent sunburn, photoimmune suppression, photoaging, photocarcinogenicity, and photosensitive disorders – but considering studies have found that people only apply 25%-75% of the testing quantity, sunscreens can’t effectively do their job, noted Dr. DeLeo, chairman of the department of dermatology at St. Luke’s-Roosevelt Hospital Center and Beth Israel Medical Center in New York.
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Experts say that advising patients to use sunscreen isn’t enough. They must also be informed about how much of it to use over a certain period of time.
Two tablespoons of sunscreen should cover an adult’s skin surface, he said. And an 8-oz bottle of sunscreen contains 16 tablespoons. Therefore, a family of four at the beach should use one bottle of sunscreen every 2 days, assuming they spend 4 hours a day in the sun (based on American Academy of Dermatology recommendations that sunscreen be applied at least every 2 hours).
Dr. DeLeo noted that a shot glass is 2.5 tablespoons, so this is a good guide for patients. Spray-on sunscreens are a good choice, because they allow patients to self apply to their backs and are a quicker way to coat impatient children. However, 2 tablespoons still need to be used with the sprays.
A recent sunscreen cost analysis found that during a 1-week beach vacation, a family of four should be spending $178-$238 a week on sunscreen, he said. This cost can be brought down by 33% if sun protective clothing is worn, and by 44% if large volumes of sunscreen are purchased. The same cost analysis also found that a transplant patient should be spending $249-$292 per year on sunscreen (J. Am. Acad. Dermatol. 2011;65:e73-9).
It is also important to remind patients that mixing an SPF 10 sunscreen with an SPF 20 will only give them an SPF of 15, he said. And while an SPF 30 may allow patients to stay in the sun twice as long as an SPF 15 with the same amount of protection, it does not offer 100% protection from burning rays.
Sunscreens with an SPF 10 block 90% of damaging rays, SPF 15 blocks 92.5%, SPF 20 blocks 95%, and SPF 40 blocks 97.5%, he noted. Always recommend a high SPF sunscreen to patients, because chances are they are not using enough of whatever they are putting on, he said.
Dr. DeLeo reported relationships with La Roche-Posay, Estée Lauder, Mary Kay, Galderma, Johnson & Johnson, and Pfizer.