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An update on sunscreen
As summer approaches, inform your patients about the importance of sun protection.
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Now that summer has arrived, it is time to review and update information regarding the use of sunscreens for sun protection. Within the past one or two years, new information relating to sunscreens has been reported, including the recent availability of a new sunscreen agent and the proposal of new rules for sunscreen use.
A brief review of ultraviolet (UV) sunlight and radiation is helpful in the discussion of sunscreens and sun protection factor (SPF) ratings. UV light is composed of UVA and UVB radiation. Most UV light reaching the ground, up to 95%, is UVA radiation. UVA radiation penetrates into the dermis and results in tanning, phototoxicity and photoaging. The relatively deep penetration of UVA radiation into the dermis results in significant changes in skin structure and architecture, resulting in the effects of photoaging. UVB radiation is absorbed in the epidermis, which is not as deep into the skin as UVA radiation, and causes erythema (ie, sunburn). Both UVA and UVB radiation can produce DNA changes and skin cancer. UVB radiation is more apparent in the summer, but UVA radiation remains constant throughout the day and the year. Thus, protection from both UVA and UVB radiation is important to maintain skin health and to protect from the harmful effects of UV radiation.
Sunscreen users are aware of a product’s SPF rating. The SPF rating, used on all sunscreen products, is a relative term describing the protection from UV radiation relative to damage to the skin from UV radiation without sunscreen. SPF refers to the quantity of UV radiation required to produce sunburn on skin protected with sunscreen, relative to the quantity of UV radiation required for sunburn on unprotected skin. Protection from sunburn increases as the SPF rating increases. The SPF rating refers only to protection from UVB, not UVA radiation.
It is commonly believed that use of a SPF 15 sunscreen product allows the user to remain in the sun 15 times longer than without sunscreen for a similar effect on the skin (eg, no sunburn or only mild sunburn). Although time exposed to sunlight is an important component of sunburn risk, other factors also are important. Thus, the concept of “15 times longer in the sun” is not totally correct. SPF rating more appropriately refers to exposure to the amount of UV radiation. Although the amount of UV radiation is related to exposure time, intensity of UV radiation (ie, more intense at midday), skin type and the method and appropriate use of sunscreen (eg, frequent application) are other important factors that affect sun protection and SPF. Thus, SPF is a relative measure of the amount of sunburn protection provided by the sunscreen product. SPF does not imply or relate to the time an individual can spend in the sun without becoming sunburned.
Sunscreen agents
Several specific chemical agents are contained in sunscreen products. These chemical agents act to absorb different wavelengths of UV radiation, primarily UVB radiation. For example, octyl methoxycinnamate (octinoxate) is a common agent in sunscreen products and absorbs UV radiation in the 290 nm to 320 nm range (UVB). Nearly all sunscreen products include more than one chemical agent. Products containing several ingredients, which together are capable of absorbing UV radiation in varying ranges (UVA and UVB), are referred to as broad spectrum. Agents that absorb primarily UVA radiation include avobenzone (Parsol 1789) and oxybenzone. It has been shown that some of the chemical agents can degrade upon exposure to UV light. Frequent application of the sunscreen product can overcome the effects of this loss in UV protection potency.
Two agents are available that function to reflect UV light, and are termed physical agents – titanium dioxide and zinc oxide. These agents block UVA and UVB radiation. Titanium dioxide and zinc oxide, typically associated with the whitish paste on a lifeguard’s face, can be thick and pasty, although some products are available that contain more easily applied forms of these physical agents.
A new sunscreen agent has recently become available, ecamsule (Mexoryl SX). It is the first FDA-approved agent in nearly 20 years. Ecamsule 2% is found in Anthelios SX (L’Oreal), which also contains avobenzone and octocrylene and has an SPF 15 rating. Ecamsule absorbs UV light in the range of 290 nm to 400 nm (UVA and UVB).
Evidence for a clinical benefit of ecamsule over other sunscreen agents is limited, at best. Bissonnette et al., evaluated the UVA protective effects of six sunscreen products (all SPF 20 or greater) in a double-blind manner. Sunscreen was applied (2 mg/cm2) to the backs of 12 volunteers and UV light from a metal halide lamp in five different UV doses, was applied for two hours to the volunteers’ skin. UV radiation effects on the exposed skin were evaluated by visual inspection and the use of a colorimeter.
One of the products tested contained ecamsule 3.3%, and this product provided statistically significant greater protection than the other tested agents, including titanium dioxide and zinc oxide from the highest dose of UV light when measured by both visual inspection and colorimeter. Although this study is useful, the specific product tested contained ecamsule in a 3.3% concentration, and the product contained a total of four sunscreen agents. Anthelios SX contains ecamsule 2% and two other agents. The study results also showed that the sunscreen products with the least protective effects had the second and third highest SPF ratings (ie, 45 and 50).
New FDA regulations
The consumers’ method of comparing sunscreen products by their SPF ratings has limitations. One important limitation relates to lack of a means to compare the relative protective effects of sunscreen products against UVA radiation. New regulations proposed by the FDA in 2007 include a simple, consumer-friendly method to compare the protective effects of sunscreen products against UVA radiation. The regulation would evaluate products with a ratings scale of one to four stars — one star is “low” protection, and four stars is “highest” protection. Products without UVA protection would be labeled as such.
Other changes proposed by the FDA include wording changes to sunscreen product labeling, urging consumers to apply sunscreens “liberally” or “generously” and to apply sunscreens frequently, at least every two hours. New warnings also would be noticeable on sunscreen products, indicating that sunscreens alone do not offer complete protection from the sun. The SPF acronym meaning would also be changed to “sunburn protection factor,” and would be listed adjacent to “UVB” to indicate that SPF reflects sunburn protection from UVB radiation. SPF values also would increase from SPF 30 to SPF 50+.
The FDA is currently in the process of evaluating the numerous public comments on these proposed rules, and it is not known when the proposed rules will come into effect, or what the specific wording will be. However, some sunscreen manufacturers have begun to alter product labeling to include the proposed rules. Some products with the UVA rating scale may be available on store shelves this season.
Appropriate use
Numerous sunscreen products are available to consumers. Sunscreen forms include lotions, foams, gels, sticks, creams, oils and lip balms. Many products are marketed for use with children, and these products can be useful because they are available in brightly-colored liquids. The AAP and the American Academy of Dermatology recommend use of a sunscreen product with a SPF rating of at least 15.
The appropriate use of sunscreen is very important to discuss with patients. Sunscreens should be applied 30 minutes prior to sun exposure, because this allows time for sunscreen absorption. Perhaps most important for users to understand is the amount and frequency of application. Most sunscreen users likely do not apply enough sunscreen or apply sunscreen frequently enough. For an average-sized adult, at least 1 to 2 ounces (2 to 4 tablespoons) should be applied, and this amount should be reapplied every two hours. A sunscreen layer of 2 mg/cm2 should be used.
To evaluate this concept, Faurschou et al. applied an SPF 4 sunscreen to the backs of 20 volunteers in four different amounts: 0.5 mg/cm2, 1 mg/cm2, 2 mg/cm2, and 4 mg/cm2. After exposure to UV light through UVB tubes, the protective effects of the varying amounts of sunscreen were measured. Application of the 0.5 mg/cm2 amount lowered the actual SPF to 1.4, and 1 mg/cm2 caused the SPF to decrease to 2. Applying 2 mg/cm2 resulted in an actual SPF of 4, and 4 mg/cm2 resulted in an SPF of 16.9. Thus, the amount of sunscreen applied is important, and lower amounts effectively reduce the SPF of the product.
Sunscreen also should be reapplied after swimming and sweating during heavy exercise. Products labeled as water-resistant or water–sweat-resistant should maintain protection for 40 minutes, and products labeled very water-resistant or very water–sweat-resistant should maintain protection for 80 minutes of swimming or sweating.
Product choice can be guided by SPF rating, broad-spectrum protection and price. A Consumer Reports evaluation in 2007 found 14 products to vary in price from $0.63 to $9.38 per ounce. The new product, Anthelios SX, is available for approximately $8.53 per ounce (approximately $29 for a 3.4 ounce tube). Products combining sunscreen agents and insect repellents should probably not be used because an insect repellent should not be applied nearly as often as a sunscreen. If sunscreens and an insect repellent are used concomitantly, sunscreen should be applied first, followed by application of the insect repellent.
Sunscreens can provide significant protection from UV radiation. However, other sun protective measures should be used, such as avoidance of the sun when possible. The proper use of sunscreen is essential to provide this protection, and it is likely that many sunscreen users do not receive adequate protection from these products because of inappropriate product use. New regulations and required product labeling as recommended by the FDA may be useful in assuring proper sunscreen use.
For more information:
- Edward Bell, PharmD, is a Professor of Pharmacy Practice at Drake University College of Blank Children’s Hospital in Des Moines, Iowa.
- Bissonnette R, Allas S, Moyal D, Provost N. Comparison of UVA protection afforded by high sun protection factor sunscreens. J Am Acad Dermatol. 2000;43:1036-1038.
- Faurschou H, Hulf HC. The relationship between sun protection factor and amount of sunscreen applied in vivo. Br J Dermatol. 2007;156:716-719.
- A new sunscreen agent. Med Lett Drugs Ther. 2007;49:41-43.
- Sunscreens: some are short on protection. Consumer Reports. 2007;July:6. www.consumerreports.org/cro/home-garden/beauty-personal-care/skincare/sunscreen-7-07/overview/0707_sunscreen.htm? resultPageIndex=1&resultIndex=2&searchTerm=sunscreen