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Sunning for Science:

The Effects of Common Substances on Sun-Exposed Skin

By Carol Lewis

A beauty-conscious public clamors for cosmetics formulated to give a more youthful look. Yet some ignore the warnings of premature aging and worse to pursue a love affair with the sun. Others prefer the needle-and-ink approach when it comes to skin enhancement. The once-taboo practice of tattooing in its various forms has moved out of seedy parlors frequented by bikers and sailors and onto the backs, shoulders, ankles, and arms of mainstream America.

These obsessions with appearance have one thing in common: skin--the largest organ of the human body.

Sensitive enough to feel a gentle breeze, yet tough enough to resist all kinds of environmental assaults, skin creates the first line of defense against possible invasion by bacteria and other germs. Skin also secretes lubricating fluids that serve as a barrier to toxic substances.

Skin can be a virtual open book to a person's state of health. Very red skin, for example, may mean high blood pressure, while sagging, leathery skin is the hallmark of a long-time smoker or sun-worshipper.

Experts already know that exposure to ultraviolet radiation (UVR), either from sunlight or by artificial sources, contributes to the risk of developing skin cancer. Now, because of the public's increasing exposure to UVR through outdoor activities and more frequent use of artificial sources, the Food and Drug Administration's National Center for Toxicological Research (NCTR) in Jefferson, Ark., is studying whether the combination of sun and the ingredients found in cosmetics or the chemicals used in tattoo inks can be linked to toxic effects or cancer.

The Skin You're In

Sunlight reduces the skin's elasticity, leading to premature aging in the form of early wrinkles. Since sun damage may not be immediately visible, many people don't realize the dangers of tanning. In fact, any tan is a sign of adaptation of the skin to potentially damaging UVR. Tanning occurs when the skin produces additional coloring (pigment) to protect itself against sunburn. The most serious consequence of overexposure to the sun is skin cancer, a delayed effect that usually doesn't show up for many years.

Health and Human Services Secretary Tommy G. Thompson strongly warns young people to take simple preventive steps now to help avoid skin cancer later. "Even a few serious sunburns," he says, "can increase a person's risk for skin cancer." (See "Reducing the Risk for Skin Cancer.")

Sunburn is associated with the shorter wavelengths of UVR, known as ultraviolet B (UVB). The longer wavelengths, known as ultraviolet A (UVA), however, can penetrate the skin and damage connective tissue at deeper levels, even if the skin's surface feels cool. It is important to limit exposure to both UVA and UVB.

Sunlamps used for tanning produce UVR. FDA policies require sunlamp product manufacturers to develop an exposure schedule and establish a maximum recommended exposure time based on the UVR emission characteristics of their products. The agency also warns that, while some tanning operators may claim that UVA sunlamps are safer than both the sun and UVB lamps, this has not been definitely shown. In fact, exposure to UVR from sunlamps adds to the total amount of UVR people get from the sun during their lifetimes, potentially increasing their risk of cancer.

Physicians and scientists are especially concerned that cases of skin cancer--the most common type of cancer in the United States, according to the National Cancer Institute--will continue to increase as people now in their teens and twenties reach middle age. The incidence of skin cancer is increasing each year, and melanoma, the most serious form, is increasing by 3 percent annually. In fact, statistics indicate that 1 out of 7 people in the United States will develop some form of skin cancer during their lifetimes.

Many dermatologists believe that there may be a link between childhood sunburns and melanoma later in life. Linda L. Lutz, M.D., assistant professor of dermatology at the University of Maryland in Baltimore, says, "Most of the sun damage we receive is before age 20. It's the cumulative effect of sun exposure that causes problems."

While the link between sun exposure and skin cancer has been established, FDA scientists are looking into the effects of the thousands of chemicals that go into commonly used cosmetics and what effects, if any, the chemicals may have on the skin when combined with sunlight.

Testing the Safety of Chemicals

Today, more than 80,000 chemicals are registered for use in the United States in everyday items such as foods, drugs, and personal care products, according to the Department of Health and Human Services' National Toxicology Program (NTP). An estimated 2,000 new ones are introduced each year. The effects of many of these chemicals on health are unknown. For scientists in general and regulatory agencies in particular, the tasks of researching and regulating these chemicals are daunting. Since the FDA is responsible for protecting the public health in regard to chemicals included in foods, drugs, and cosmetics, research at NCTR contributes to the FDA's ability to regulate and ensure the safe use of products containing these ingredients. NCTR studies investigate the toxicity of these chemicals, contributing to a database used by the FDA to make regulatory decisions.

The NTP is based at the National Institute of Environmental Health Sciences (NIEHS), one of the National Institutes of Health. It was established in 1978 to set priorities and coordinate the testing of chemicals that the public may be exposed to. Advised by several government agencies, the NTP manages information on potentially hazardous chemicals added to a variety of industrial and consumer products, as well as those occurring in food naturally or as unintentional contaminants.

The FDA and the NIEHS established an interagency agreement in 1992 to cooperate on toxicological studies. The agencies recognized the need for toxicological testing on chemicals in the presence of sunlight (phototoxicology). The result, in 1998, was the construction of a new laboratory, designated as the NTP's Center for Phototoxicology (NCP).

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

For more information, visit the Centers for Disease Control and Prevention's Web site.

Source: Centers for Disease Control and Prevention