Researchers at the University of California San Francisco report good news for the large proportion of American women, and some men, who use hair color products. In a study that included 4,108 participants, researchers found that there is no association between normal use of hair color products and risk for non-Hodgkin's lymphoma (NHL), the fifth most common cancer in the United States among both women and men.
The results of the study will be published in the December 1 issue of the American Journal of Public Health.
"These are wonderfully negative results," said Elizabeth Holly, Ph.D., MPH, UCSF professor of cancer epidemiology studies and lead author of the study. "There have been some studies that have shown an association between use of hair color products and non-Hodgkin's lymphoma, but results were often based on a small number of people who used hair dye and got lymphoma."
She cited a 1992 study that concluded that women who ever used any type of hair color product were at a 50 percent increased risk for NHL. However, she said that the present study included twice as many women and four times the number of men with NHL who had used hair color products than the 1992 study and found no overall increased risk among these populations.
"The results of our study, the largest one ever conducted in this area, will hopefully make the large proportion of American women who color their hair feel much more comfortable about using these products," Holly said.
Between 20 to 40 percent of women in the U.S. use hair color products, and the percentage is even higher in other regions of the country such as the San Francisco Bay Area, where 56 percent of women, and 9 percent of men interviewed during the study reported ever using hair color products.
According to Holly, researchers found that these percentages regarding hair color use were exactly the same among populations of people with and without NHL. The similarity of these proportions supports the assertion that there is no associated risk of hair color product use and NHL.
"The results of our study indicate that hair dye use is an unlikely risk factor for non-Hodgkins lymphoma and this should prompt researchers to focus on other etiological clues associated with lymphoma such as medical history, diet, exercise, lifestyle and perhaps occupation," Holly said.
Besides investigating the association between hair product use and NHL during the study, UCSF researchers also examined various occupational and chemical exposures, sexual factors, allergies, and viruses as potential risk factors for the disease.
According to Holly, over the past two decades, the incidence of NHL among the American population has surpassed most other cancers; increasing 4 percent per year in men, and 3 percent per year in women. However, known risk factors only explain a small portion of the estimated rise in incidence of NHL that has occurred since the late 1940's. In addition, similar increases have been reported by other countries and cannot be accounted for by known changes in exposure or NHL diagnostic techniques.
Epidemiological studies have provided conflicting reports regarding the association between hair color use and cancer, Holly said. While early laboratory animal studies found that many hair color products were carcinogenic to varying degrees, subsequent research on hair color components found that, with normal use, these products did not cause cancer in humans.
In addition, over the past 20 years, the Food and Drug Administration has discontinued some hair color products that were considered carcinogenic in animals. But Holly said that critics of these animal studies assert that researchers used high concentrations that would not normally be used by humans to evaluate the risk of exposure to chemicals used in hair dyes.
The Northern California Cancer Center helped recruit patients for the study. They identified NHL patients between 21 and 74 years of age within one month of diagnosis with NHL in all of the 70 hospitals located in the six San Francisco Bay Area counties. 713 study participants recently diagnosed with NHL were identified and interviewed about their hair color product use. 1604 control subjects, who were identified using random digit dial and matched to NHL patients by gender, age within five years, and county of residence, were also interviewed about hair color product use.
Study participants were asked if they had used hair color products more than five times not including during the past year and, if so, the type of product used and age at first and last use, frequency of use per year, and colors of permanent dyes used.
The National Cancer Institute funded this study. Other researchers of the study include Chitra Lele, Ph.D.; and Paige M. Bracci, PMH, MS.
Journal
American Journal of Public Health