Researchers from Rutgers University in Piscataway, N.J., tested skin moisturizing creams on mice to determine whether their use is linked to cancer. To do this, they exposed hairless mice to ultraviolet radiation to mimic sun exposure, and afterward treated the mice with one of four popular moisturizers -- Dermabase, Dermavan, Eucerin or Vanicream.
They found that the mice treated with moisturizers after the exposure to ultraviolet light grew more skin tumors -- and that these tumors were larger than those on untreated mice.
Lead investigator Allan Conney, a professor of cancer and leukemia research at Rutgers, said the study should cause concern over the safety of many moisturizers.
"I think it raises a red flag indicating that there's a need to determine whether or not these products could cause this problem in people," Conney said. "And we really don't know that from this study, which looked only at mice. ... People aren't mice."
However, the researchers wrote in the report, the cancer-causing properties of these moisturizers might in part explain the rise in skin cancer cases over the last few years.
Of Mice and Men
Already, skin cancer affects thousands of Americans each year. The American Cancer Society estimates that each year 59,940 people will be diagnosed with melanoma, the most serious form of skin cancer, and that about 8,400 people will die from the disease.
These cases appear to be on the rise. A report published in the July issue of the Journal of Investigative Dermatology, which analyzed more than 20,000 cases of melanoma in people between the ages of 15 and 39, found that the incidence of melanoma in young women rose to 13.9 per 100,000 people in 2004, up from 9.4 per 100,000 people in 1980. In young men, melanoma rates leveled off between 1980 and 2004, settling at 7.7 per 100,000 people in 2004.
But should we blame moisturizers for the rise? Some dermatology experts warn that the use of moisturizers should not be made a scapegoat for this increase in skin cancer cases.
"I was sitting in a room full of dermatologists at a dermatology conference in North Carolina when I heard about this study, and not one of us could come up with a logical reason why a skin moisturizer would increase your risk for skin cancer," said Dr. Darrell Rigel, a clinical professor of dermatology at New York University's Langone Medical Center.
"Moisturizers don't have any risk of skin cancer in other models," said Dr. Steven Feldman, a professor of dermatology, pathology and public health sciences at Wake Forest University, in Winston-Salem, N.C. "The components in moisturizers are tested. There's no evidence for this being a problem in humans."
Still, some experts point out that baby oil -- a product popularly used as a substitute for tanning oil -- can be used to increase the absorption of sunlight into the skin. They said that perhaps some skin moisturizers hold similar light-absorbing properties.
"Moisturizers improve UV penetration of skin," said Dr. Alice Pentland, a professor and chair of dermatology at the University of Rochester. "Absorbed light can cause skin changes, while reflected light can't. ... So the findings aren't too surprising."
But in this study, moisturizer was only applied after UV light exposure. And many experts noted that the study has other confounding factors that make it hard for them to take the findings seriously.
One issue is the fact that the hairless mice used in the research were already at very high risk for developing skin tumors. Even among the group of control mice who were not treated with skin moisturizers, 80 percent to 90 percent of the mice developed tumors.
"With 80 percent of control mice developing tumors, it would be exceedingly difficult to say that there was a statistically significant difference between treated and untreated mice," said Dr. Carolyn Jacob, director of Chicago Cosmetic Surgery and Dermatology.
Rigel pointed out another issue with studying melanoma in animal models: The type of skin cancer that develops in humans is vastly different from what is found in animals.
"Melanoma is not a cancer we can extrapolate from mice," Rigel said. "We can't test these things on animal models because this type of skin cancer is so unique to humans."
Most dermatology experts echoed Rigel's concerns. "Further research needs to be done to determine if moisturizers alone increase risk of skin cancer," Jacob said.
Marketing? There's the Rub
Despite the uncertainty of whether or not these findings have any implication for humans, the study researchers have already teamed up with Johnson & amp; Johnson to patent a "custom blend" moisturizer that does not increase tumors in mice.
But experts urge consumers to think twice before throwing out the old moisturizer and shelling out more cash for the new J& J concoction.
"I think J& J probably has a formulation that is more light-scattering, so more light would be reflected. I wouldn't pay any extra money for that property," said Pentland. "To avoid skin cancer, people need to be sensible about sun exposure and specifically protect themselves from too much sun."
Feldman's advice is much more pointed: "Don't let some mouse study get you nervous."