Interview with Dr. Sommerville


Q. Are all sunscreens created equal especially if they bear the same Sun Protection Factor (SPF) number?

Dr. Sommerville: Expressed as a ratio of the Minimal Erythema Dose (MED) for sunscreen-protected skin to the MED for unprotected skin translating to the length of time a sunscreen prevents skin reddening from UVB compared to how long it takes to redden without a sunscreen, the SPF measures protection only from UVB radiation. SPF rating gives no indication of user’s protection against UVA radiation which is also implicated in photocarcinogenesis (ultraviolet-induced skin cancer formation) trough suppression of the immune system. UVA rays are also responsible for up to 80% of skin aging. Some of the manifestations of skin aging include hyperpigmentation, leathery appearance, wrinkles, blotchiness, tactile roughness and telangiectasias (broken capillaries). Since there is currently no well-established scale for measuring the protection against the UVA, one must consider the sunscreen ingredients, some of which offer relatively good level of protection against UVA.

Another frequent misconception about the SPF factor is that a product with SPF30 must provide twice the protection against sunburn as a product rated SPF15. This is not true since a product rated SPF15 may screen about 94% of UVB radiation whereas a product at SPF30 would screen about 97%. Additional protection provided by products rated above 30 is trivial.

Q. Does one need to wear sunscreen in the winter and does the window glass protect us from the damaging effects of the sun rays?

Dr. Sommerville: UVA rays are much more numerous that UVB rays and out of the ultraviolet rays that reach the skin, only 5% are UVB and up to 95% are UVA rays. Unlike the UVB rays, UVA rays penetrate through windows as well as most kinds of glass. Unlike the UVB rays that mostly remain at the epidermis, UVA rays penetrate deeper into the dermis and damage collagen and elastin causing premature aging. While sunburn indicates skin damage from UVB rays, physical damage from UVA rays may not be immediately apparent. Furthermore, UVA levels are relatively constant year-round while UVB levels tend to be lower in the winter months. UVB is most intense during midday roughly from 10:00AM to 3:00 PM while UVA levels are relatively even throughout the day. These are some of the reasons while it is important to protect the skin from the harmful effects of the sun throughout the year. It also matters which sunscreen you choose since most sunscreens are only protective against the UVB rays are ineffective against the UVA part of the solar spectrum. Avobenzone is an effective UVA photoprotectant but unfortunately, it is easily degraded when exposed to sunlight (photounstable). The most effective UVA sunscreens contain Mexoryl and avobenzone combination which is photostable or Helioplex, a chemical compound that also stabilizes avobenzone. Physical sunblock such as Zinc oxide and titanium dioxide also offer relatively broad-spectrum protection against both UVA and UVB rays.

Q. How should one use the sunscreen to maximize its benefits?

Dr. Sommerville: One should use sunscreen of SPF15 or higher and apply 1 ounce (2 tablespoons) of sunscreen per the entire body 30 minutes before going outside. One should reapply every 2 hours while remaining outdoors.

Q. What is the most important message that you would like to convey to your patients?

Dr. Sommerville: Most of the skin cancer is preventable. All it takes is to practice effective sun protection measures beginning in childhood. Early diagnosis is essential in ensuring that all of the skin cancers including melanoma are curable with appropriate treatment. It is important to schedule a complete body check once a year especially for patients over the age of 40 but sooner if there are risk factors present. Any mole that exhibits any of the ABCDE signs or that looks different from other moles on the body should be evaluated by the dermatologist ASAP regardless of age.