July 15, 2009

 

 Measuring sunscreens' ability to protect against skin cancer

 
Measuring sunscreens' ability to protect against skin cancer
 
posted July 1, 2009
 

Skin cancer is the most common type of cancer in the United States, with more than 1 million new cases diagnosed each year.

It is also among the most costly, with annual direct and indirect costs estimated at $2.5 billion. GHLIT paid about $444,000 for treatment of malignant neoplasm of the skin/melanoma in 2008 and approximately $564,000 in 2007.

Because it is linked closely to ultraviolet radiation exposure, skin cancer is of particular concern for veterinarians, especially those in large animal practice. Several studies suggest sunlight exposure is responsible for an elevated rate of skin cancer among veterinarians whose practices are not limited to small animals.

Sunscreen use has long been considered the primary line of defense against skin cancer. But it may not provide sufficient protection against malignant melanoma, which is the rarest but deadliest form of skin cancer. Melanoma is responsible for more than 75 percent of skin cancer deaths.  

SPF protection isn't enough

Sun protection factor, or SPF, scores provide a measurement of the protection sunscreens provide against UVB rays, which cause the most immediate damage to the skin. But the number says nothing about the protection against UVA rays, which penetrate more deeply into the skin and reach fragile subcutaneous tissues. 
 

That is why the Food and Drug Administration is finalizing regulations that will require sunscreen manufacturers to provide UVA protection information on their product labels. The new regulations will require sunscreen testing, and current plans involve using those test results to label products with a four-star rating system, with one star representing the lowest UVA protection.

"While sunscreens have improved dramatically over the past several years, there was a need to update the governmental regulations associated with sunscreens, especially regarding the institution of a UVA test method and product labeling," Perry Robins, MD, president of The Skin Cancer Foundation, said in a written statement.

"Our knowledge of the dangers associated with UVA rays has grown significantly over the last few decades. We now know that UVA plays a very direct role in skin cancer, comparable to that of UVB. Therefore, introducing a UVA test method will enable consumers to know how well the product protects against UVA rays as well as UVB rays."

The new regulations will also prohibit use of the words "sunblock," "waterproof," "sweat-proof" and "all-day protection." They will also ban claims that sunscreens have SPF ratings in excess of 50 unless those claims are backed by scientific evidence.

The latter change is important because a higher SPF rating does not necessarily mean the product will provide more protection against UVB rays. Sunscreens with SPF 15 ratings block about 93 percent of incoming UVB rays, while SPF 30-rated products block 97 percent, and SPF 50 products block 99 percent. No sunscreen blocks 100 percent of UVB rays.  

Cover up for maximum protection

The new FDA regulations would also require sunscreen manufacturers to include on product labels an alert that a comprehensive sun protection regimen includes limiting time in the sun and wearing protective clothing. 
 

A comprehensive review of more than 200 studies on sun protection, which appeared in The Lancet, found sunscreen was effective at protecting against basal carcinomas and squamous cell carcinoma, the two most common forms of skin cancer. But there was no conclusive evidence that sunscreen offered any protection against melanoma.

Instead, researchers led by Stephan Lautenschlager, MD, with Switzerland's Triemli Hospital found that avoiding direct sunlight and wearing clothing that stops UV rays from reaching the skin are the best ways to prevent skin cancer. They also found that tightly woven, thick garments made of denim, wool, or polyester provide the best protection.

The authors acknowledged that many prefer using sunscreen over wearing protective clothing, but they warned that sunscreen should not be used to increase the amount of time spent in direct sunlight. They also urged better education on the types and proper use of sunscreen.

Of the two types of sunscreen available, inorganic is the least popular because of its opacity, which is caused by zinc and titanium oxides that scatter UV light. But inorganic sunscreens are generally well-tolerated and cause far fewer allergic reactions than organic counterparts.

The more popular sunscreens consist of organic molecules that blend to give photoprotective qualities and absorb UV rays. Proper use involves applying at least one ounce between 15 and 30 minutes prior to sun exposure and reapplication every two hours, with more frequent reapplications when perspiring heavily or swimming. The best organic sunscreen protects against UVA and UVB rays and is waterproof or water-resistant.

"The application of a liberal quantity of sunscreen is by far the most important factor for effectiveness of the sunscreen, followed by the uniformity of application and the specific absorption spectrum of the agent used," the researchers wrote.