Common Substances and Sun-Exposed Skin : Part 2

by Food and Drug Administration (FDA)

(Page 2 of 2)

Paul C. Howard, Ph.D., director of the laboratory, says that one of the program's objectives is to provide reliable short-term testing of carefully selected compounds that are in wide use and that may affect public health. "We not only test the outcome of the combined use of a product and light on an animal," Howard says, "we additionally try to determine the mechanism by which the chemical affects the animal."

The NCP tests not only cosmetic chemicals but also other potentially light-sensitive (photoactive) drugs and substances to assess if they can become toxic or increase cancer risks in combination with UVR. For example, foods such as celery and herbal remedies such as St. John's wort both contain chemicals that react to sunlight.

"This unique facility evaluates the toxicity of compounds for which the FDA has regulatory responsibility, but which have not been tested by current standards," says NCTR Director Daniel A. Casciano, Ph.D.

The NTP invites and encourages government and private organizations and the general public to nominate chemicals and other substances for study. Member agencies that are the primary sources for nominations include the FDA, the NIEHS, and the National Institute for Occupational Safety and Health.

Each nomination goes through a selection process. Substances selected are generally of greatest concern for public or occupational health based on the extent of human exposure or suspected toxicity. Once a chemical is recommended for testing, the recommendation is published in the Federal Register for public comment. Following the approval of a nomination, studies are designed and implemented as time and resources permit.

Ongoing Research

Research is now being done for the FDA on alpha- and beta-hydroxy acids — two components common in a large number of skin-care creams and lotions used in the United States. Many of these lotions are marketed as aids to correct sun-damaged skin. The studies are being conducted to determine if there is a relationship between the appearance of sunlight-induced skin cancer and the continuous use of these topically applied acids. The FDA's Center for Food Safety and Applied Nutrition, which generally regulates cosmetics after they are on the market, nominated the alpha-hydroxy acids in 1998 because they are used by millions of people (mostly women). In addition, short-term studies had suggested that their use enhanced skin sensitivity to ultraviolet light.

The FDA has particular concerns that, unlike traditional cosmetics, these acids might peel away layers of the skin to the point where sunlight can damage DNA in cells at the skin's deepest levels and promote skin cancer. And so, says Howard, "vanity may have a price." The question, he says, is "whether the use of these acids causes a change in skin cancer rates, and if so, whether glycolic acid (an alpha-hydroxy) and salicylic acid (the most widely used beta-hydroxy acid) work differently."

To begin answering this question, the spectrum of sunlight to which humans are normally exposed had to be simulated in the laboratory using 6,500-watt, xenon-arc lamps. With this equipment, Howard says, "We can mimic sunlight from anywhere on the planet." In addition, the laboratory is equipped to generate any combination of fluorescent radiation, such as UVA and UVB lamps and tanning lamps. This means that the NCP can experimentally reproduce nearly any source of light to which humans are exposed.

In the ongoing experiment involving alpha-hydroxy acids, test creams are applied to the backs of specially bred hairless mice. The mice are then placed two meters from the light source, and they receive a dose of light that is less than 10 percent of the amount required to elicit a sunburn. The intensity of the light at two meters is equivalent to about 25 percent of the intensity of noon summer sunlight. "NCP is capable of determining the impact of this light on the toxicity or carcinogenicity of chemicals," says Howard.

The research involved in these studies is long-term, and, as a result, none of the studies has progressed to the point at which their results can guide public health decisions. For example, it can take up to a year to set up the study protocol and conduct preliminary toxicity studies, another year to conduct the study, a half year to complete pathological tissue analyses, and another six months to complete audits and finalize reports. A one-year study, therefore, actually can take between three and four years to complete.

Other studies at NCTR that are part of the interagency agreement with NTP have been completed and are at the "cusp" of influencing public health decisions, according to Howard. Studies conducted on fumonisin (a fungus present on corn worldwide), for example, were used by the FDA and the World Health Organization to determine acceptable levels of the toxin in products intended for human and animal consumption.

"The Center for Phototoxicology," Howard adds, "is just a small part of a larger effort at NCTR and the NTP."

Aloe vera (marketed as a cosmetic ingredient among other skin-care uses), retinyl palmitate (used to correct unwanted skin lesions), and tattoo pigments are currently being studied simultaneously. Ongoing research may include dozens of chemicals at one time.

Future Scientific Studies

Many other compounds, including sunblock chemicals, tanning enhancers, skin colorants, and tattoo inks are candidates for future NCP studies to determine whether UVR or simulated solar light induce toxicity and cancer in laboratory animals.

With regard to tattoos, Howard says considerable change has taken place in the use and social acceptance of tattooing since the 1990s. "It used to be 'Go Marines,'" says Howard. "Now it's a Picasso." Wider use is making these kinds of chemicals likely candidates for NTP studies.

In short, "We are conducting studies that will address the public health impact of many cosmetics and chemicals in the presence of sunlight," adds Howard, "and are providing the FDA and NTP with an additional resource to bring to bear on a chemical of questionable or unknown safety."

Reducing the Risk for Skin Cancer

• Wear clothes, hats and sunglasses to protect the skin.
• Use a sunscreen effective against UVA and UVB radiation and with a sun protection factor of 15 or more.
• Limit exposure to the sun during the peak hours between 10 a.m. and 4 p.m.
• Seek shade, especially from the midday sun.

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.