"Sunscreens are a helpful tool, but they are not perfect and their deficiencies are compounded by the fact that they are often not used properly," says Dr. Spencer, clinical professor of dermatology, Mt. Sinai School of Medicine, New York, and a private practitioner in St. Petersburg, Fla.
"Consumers need to be instructed to look for a broad-spectrum sunscreen with an SPF of 15 or higher, apply the product liberally, and re-apply it often, but they also must combine sunscreen use with sun avoidance and wearing of protective clothing," he says.Domestic versus foreign
Dr. Spencer explains that sunscreens were originally developed by Navy researchers seeking to create a product that would allow sailors to remain on duty longer. Their goal was to design a formulation able to prevent burning from ultraviolet B (UVB) exposure (290 nm to 320 nm). However, natural sunlight, on average, is composed of about 95 percent UVA (greater than 320 nm to 400 nm), and only relatively recently have the hazards of UVA become appreciated. While the more energetic photons of the UVB spectrum are responsible for sunburn, the longer UVA wavelengths penetrate deeper into the skin. Not only are they carcinogenic, but they also play a role in causing the cellular and structural changes that are seen clinically as photoaging.
Dr. Spencer says sunscreens currently sold in the United States contain UVB blockers that are "very, very good," but the three main ingredients used for UVA protection — titanium dioxide, zinc oxide and avobenzone (Parsol 1789) — are suboptimal. Better UVA blockers do exist — the camphor derivatives Mexoryl LX and Mexoryl SX (L'Oréal) and Tinosorb (Ciba) — and sunscreen products containing those agents are available outside of the United States. However, Americans are still waiting for the day when they do not have to resort to ordering those products online or stocking up on them when they travel to other countries.
U.S. regulations and marketing
"Titanium dioxide and zinc oxide are physical blockers that protect against the effects of UV light throughout the UVB and UVA range. However, to be optimally effective, they would have to be formulated in higher concentrations than those currently used," Dr. Spencer tells Cosmetic Surgery Times.
"The trade-off would be products that are chalky, opaque, and have poor consumer acceptance. At the concentrations used, Parsol 1789 blocks a higher proportion of UVA light, but its blocking ability trails off in the longer UVA wavelength range, and there is also concern about its stability and, particularly, its potential to be degraded by UV light."
Mexoryl and Tinosorb overcome the limitations of Parsol 1789, but regulatory issues have presented an obstacle to the availability of those better UVA sunscreen ingredients in the United States.
"By a quirk of fate, sunscreens are classified by the FDA (Food and Drug Administration) as over-the-counter drugs rather than cosmetics, even though they are inert chemicals with no biological activity," Dr. Spencer explains. "Therefore, approval of new sunscreen ingredients requires that the manufacturer conduct rigorous clinical trials to demonstrate efficacy and safety. The difficulty and expense of such studies is a prohibitive nightmare for a company that will end up with the rights to market a product selling for $10 a tube at local retailers."
Against that background, Dr. Spencer applauds L'Oréal for submitting an NDA (New Drug Application) for the approval of Mexoryl based on clinical studies investigating its use for preventing polymorphous light eruption. FDA review is still ongoing, and if the approval comes, it is unclear whether Mexoryl will be formulated in a product that is available by prescription only or over the counter.