by Steven Q. Wang, MD
Dr. Wang is director of dermatologic surgery and dermatology at Memorial Sloan-Kettering Cancer Center at Basking Ridge, NJ. Dr. Wang is a member of The Skin Cancer Foundation’s Photobiology Committee.
Q. Does a higher-SPF (sun protection factor) sunscreen always protect your skin better than a lower-SPF sunscreen? How high should I go?
A.Sunscreens with a higher SPF should offer more protection from the sun’s harmful ultraviolet (UV) radiation, which is linked to the vast majority of skin cancers, as well as premature skin aging and eye damage. But the answer is not that simple.
UV radiation reaches the earth in the form of UVB and UVA rays. UVB radiation plays a key role in skin cancer, and SPF refers mainly to the amount of UVB protection a sunscreen offers. Thus, higher SPFs can help: An SPF 15 sunscreen blocks 93 percent of UVB radiation, while an SPF 30 sunscreen blocks nearly 97 percent. Furthermore, higher SPF values offer some safety margin, since consumers generally do not apply enough sunscreen. To evaluate SPFs, testers apply two milligrams of sunscreen per square centimeter of skin. But in everyday life, most people apply from only 0.5 to one milligram per square centimeter of skin. Consequently, the actual SPF they achieve is approximately 1/3 of the labeled value.
Despite these advantages, there are potential downsides to using products with very high SPFs. First, above SPF 50 (which blocks an estimated 98 percent of UVB rays), the increase in UVB protection is minimal. Second, although UVA protection is also important (UVA not only accelerates skin aging, but contributes to and may even initiate skin cancers), SPFs mainly measure UVB protection. Individuals applying high-SPF sunscreens may not burn (UVB is the chief cause of sunburn), but without UVA-screening ingredients they can still receive large amounts of skin-damaging radiation. To avoid such a scenario, regulatory bodies in Europe and Australia have adopted UVA testing guidelines and measurement standards, and capped the SPF of sunscreens at 50+. The US Food and Drug Administration (FDA) may do the same, but hasn’t to date.
Products with very high SPFs may also encourage individuals to neglect other photoprotective behaviors, like seeking the shade and wearing sun-protective clothing. By preventing sunburn, sunscreens with very high SPFs can create a false sense of security, prompting consumers to stay out in the sun longer. Sun damage (for example, UVA damage) can take place without skin-reddening doses of UV radiation, and even the best sunscreens should be considered just one vital part of a comprehensive sun protection regimen.
The importance of using both UVB and UVA protection cannot be emphasized enough. For patients who really wish to know “how high should I go?” I suggest products with SPFs no lower than 30 and no higher than 50. In addition to an SPF of 30+, your sunscreen should include some combination of the following UVA-blocking ingredients: zinc oxide, titanium dioxide, avobenzone, ecamsule, and oxybenzone. Sunscreens with both UVA and UVB protection may be labeled multi spectrum, broad spectrum, or UVA/UVB protection.
Published in the Spring 2010 Edition of Sun & Skin News