Hair straightening chemicals not linked to breast cancer risk in African-Americans

PHILADELPHIA - Chemical "relaxers" used to straighten hair are not associated with an increased risk of developing breast cancer among African-American women, say researchers who followed 48,167 Black Women's Health Study participants.

In the May issue of Cancer Epidemiology, Biomarkers & Prevention, researchers from Boston University and Howard University Cancer Center found no increase in breast cancer risk due to the type of hair relaxer used or the frequency and duration of use. Women who used relaxers seven or more times a year over a 20 year span or longer had the same risk as women who used the chemicals for less than a year, researchers say.

Lynn Rosenberg is professor of epidemiology at Boston University School of Public Health. She received her M.S. in chemistry from Boston University and M.S. in biostatistics and Sc.D. in epidemiology from Harvard University. Dr. Rosenberg’s research has been in the areas of cancer epidemiology, cardiovascular epidemiology, and drug epidemiology, with a recent emphasis on women’s health. She has carried out multiple studies of risk factors for cancers, including cancer of the breast, cervix, and colon, and for myocardial infarction. Particular interests have been the health effects of oral and injectable contraceptives and of noncontraceptive estrogens. Several important hypotheses have been raised by her studies: that alcohol consumption increases the incidence of breast cancer and that use of nonsteroidal anti-inflammatory drugs decreases the incidence of large bowel cancer. Both hypotheses were subsequently confirmed in numerous studies. Currently, she is PI of the long-running Case-Control Surveillance Study, which has been in progress since 1975; multiple case-control studies are conducted within the same administrative framework to assess the unanticipated effects of medications on the incidence of various cancers. She heads a cross-sectional study of the effect of injectable progestin contraceptives on bone mineral density in African women and women of mixed race in South Africa . She is also PI of the Black Women’s Health Study, the largest follow-up study of the health of African-American women yet conducted. The study, conducted in collaboration with investigators at Howard University, follows 59,000 black women from across the U.S. to assess risk factors for outcomes that include breast cancer, other cancers, hypertension, diabetes, systemic lupus erythematosus, uterine fibroids, and preterm birth. Dr. Rosenberg is the author of over 200 scientific papers.

"This is good news," said the study's lead investigator, Lynn Rosenberg, Sc.D., professor of epidemiology at Boston University School of Public Health. "The present study is definitive that hair relaxers don't cause breast cancer, as much as an epidemiologic study can be." Previous research shows that breast cancer incidence is higher among African-American women age 40 or younger than among Caucasian women of the same age, and this increased risk is not fully explained by known risk factors, such as race and family history. At all ages, African-American women are more likely to die of breast cancer than are Caucasian women. To shed light on these findings and to study potential causes of breast cancer and other serious illnesses that affect black women, the Black Women's Health Study was launched across the United States in 1995. More than 59,000 women completed an initial questionnaire and more than 80 percent have answered follow-up questions every two years since, including questions about use of hair relaxers. Hair relaxers can enter the body through cuts or lesions in the scalp. These products are not fully monitored by the Food and Drug Administration, and thus could contain potentially harmful compounds, Rosenberg said. Manufacturers of hair relaxers and hair dyes are not required to list all ingredients of their products on the packages, as some may be considered trade secrets, she said. "Because hair relaxers are more widely used by younger African-American women than they are used by older African-American women, a connection with increased risk of breast cancer in younger women seemed possible," Rosenberg said. "Also, millions of African-American women use hair relaxers, and substances that are used by millions of women over a span of many years should be monitored for safety." The researchers found that younger women used hair relaxers more than older women did. They also discovered that the majority of women used hair relaxers before age 20 and a third used the chemicals at least seven times a year.

But when they examined the association between use of hair relaxers and breast cancer, based on 574 newly diagnosed cases of breast cancer identified during the follow-up period, they found no connection between use of relaxers and breast cancer incidence overall or among the younger women, even if use had been frequent and of long duration.

The study was funded by the National Cancer Institute. Co-authors include Julie Palmer, Sc.D., and Deborah Boggs, M.S., of Boston University School of Public Health, and Lucile Adams-Campbell, Ph.D., of Howard University Cancer Center. ###

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