Sunscreens are an important part of a dermatologist’s tool kit, but they’re not a panacea for UV-induced damage, according to Dr. Timothy Berger.
Although sunscreens work well in laboratory testing, almost no one applies them in a way that will provide the advertised UV protection, Dr. Berger noted at the seminar sponsored by Skin Disease Education Foundation (SDEF). And for some patients, sunscreens can exacerbate their UV-induced problems.
Sunscreens themselves, not the vehicular preservatives, are usually the culprit when a patient presents with a complaint of being allergic to sunscreens, said Dr. Berger, a professor of dermatology at the University of California, San Francisco.
"You will usually find that the dermatitis only occurs in areas touched by the sun," he said in an interview. "The problem is often an allergy to the PABA or PABA-related substances in the sunscreen they are using."
For patients like this, the best alternative is a PABA-free sunscreen that contains zinc and titanium oxide – inert compounds that are physical barriers against UV light, rather than chemical barriers.
And although SPF ratings might look great in advertisements, it is almost a sure bet that sun-seeking patients are not getting nearly the protection promised, Dr. Berger noted. "Some interesting recent studies have looked at what SPF you actually get what you put on sunscreen. The amount used in testing is actually about four times more than what people really use."
One study found that most people apply about 0.5 mg/cm2, while the lab tests use a volume of 2 mg/cm2 to achieve the advertised SPF (J. Am. Acad. Dermatol. 2010;62:218-22). "The problem is, efficacy falls off in a very sharp way," Dr. Berger said. "If you apply SPF 30 sun block [at one-quarter the recommended amount], you only end up with an actual SPF of about 3."
"We need to make sure our patients understand this. And while most people are still not going to use the necessary amount, we can stress the importance of reapplying frequently, which can help keep the protective value up somewhat," he said.
Light Therapy for Atopy
UV light therapy is a frequent treatment for eczema and other atopic dermatoses, but for about 3% of patients, it the wrong thing to offer, Dr. Berger said. "For this small population, sun exposure actually makes the condition worse. Put them in the light box and the eczema will flare."
More than a cursory skin exam should be performed on patients with atopic dermatitis, he recommended. "Have them remove their clothing at least from the waist up. Look for eczema that has a photo distribution: It might be worse on the face and side of the neck, but beneath the chin the skin could be spared. If it looks like a photo-distributed rash, and they report a history of flare with sun exposure, then prescribing aggressive sun protection might make a big difference."
A frequently missed diagnosis in young children – particularly infants – is erythropoietic protoporphyria (EPP). "The first time these infants go out into the sun, they will start screaming, because their skin is burning," Dr. Berger said. As quickly as 1 hour after sun exposure, they may develop erythema, edema, urticarial lesions, or purpura on exposed skin.
Europeans are somewhat ahead in drug research for treating EPP, Dr. Berger noted, but the United States is catching up. The University of California is one of six U.S. study sites participating in a phase II placebo-controlled trial of afamelanotide, a synthetically produced analog of human alpha-melanocytic–stimulating hormone (alpha-MSH).
"The hope is that the drug will stimulate the production of melanin, which actually has two benefits," Dr. Berger said. "First, it’s a photo protectant, but it’s also an antioxidant."
When porphyrins absorb UV rays, they release free radicals that lead to the acute and chronic damage that occurs on EPP patient skin. The porphyrins can accumulate and damage other tissues – including the liver, which causes problems for about 20% of EPP patients. The extra melanin can help neutralize these highly reactive oxygen species and provide protection from the acute symptoms patients suffer when skin is exposed.
While afamelanotide can never cure EPP, Dr. Berger said, it might afford patients the opportunity to live a more normal life. "While they will never be going out looking for a tan, at least they may be able to enjoy being outdoors without having to be completely encased in clothing."
Dr. Berger disclosed serving as a consultant for Prescription Solutions. SDEF and this news organization are owned by Elsevier.