WAILEA, HAWAII – When sunscreens are tested for their SPF, testers apply 2 mg/cm2, but most people use only 20%-50% of that amount, which significantly reduces their protection, according to Dr. Julie C. Harper, director of the Dermatology & Skin Care Center of Birmingham, Ala.
The correct amount is 1 teaspoon of sunscreen on the face/head/neck, 1 teaspoon on each arm, 2 teaspoons on the torso, and 2 teaspoons on each leg, Dr. Harper said in a presentation at the Hawaii Dermatology Seminar provided by Global Academy for Medical Education/Skin Disease Education Foundation. Reapplication every 90 minutes to 2 hours is key to effective protection, Dr. Harper said.
However, “most people use less than one bottle of sunscreen per year,” she noted.
Prompting patients to improve their sunscreen use involves disproving some myths, Dr. Harper pointed out. When patients cite concerns about low vitamin D as a reason to avoid sunscreens, she recommended that they be counseled that there are three sources of vitamin D: foods such as fatty fish, vitamin D fortified foods, cheese, and egg yolks; vitamin D supplements; and skin synthesis through UVB exposure; and that only one of these – UVB exposure – is a known carcinogen.
Dr. Julie C. Harper
Also, some patients express concern that sunscreen itself may be a carcinogen. Oxybenzone, a common sunscreen ingredient, has demonstrated some estrogenic effects in vitro and in vivo studies. However, the rat studies often cited in support of that finding involved the use of very high doses – approximately the equivalent of 277 years of daily sunscreen application with 6% oxybenzone, a much higher concentration than is found in commercial sunscreens, she said.
For patients interested in nontopical sun protection, polypodium leucotomos extract (PLE) is an option, Dr. Harper said. PLE, an antioxidant extract from a tropical fern, can be part of a skin cancer prevention strategy that also includes good sunscreen and protective clothing. PLE works by counteracting UV-induced immunosuppression, activating the tumor suppressor p53 gene, and inhibiting cyclooxygenase-2, all of which can help protect the skin from burning.
In addition, oral nicotinamide has been shown to help repair DNA damage in human keratinocytes, and in a clinical trial, has been associated with fewer actinic keratoses and squamous cell carcinoma, compared with placebo, she said.
However, more research in these options is needed, and patients should be encouraged to follow consistent sun protection practices, Dr. Harper emphasized.
Dr. Harper disclosed relationships with companies including Allergan, Bayer, Galderma, LaRoche-Posay, Promius, Valeant, and BioPharmX.
SDEF and this news organization are owned by the same parent company.