Chemical "relaxers" commonly used by black women to straighten hair are not associated with any increased risk of developing breast cancer, according to a new study.

Researchers found women who used hair relaxers seven or more times per year over a period of 20 years or longer had the same risk of breast cancer as those who had used the products for less than a year.

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"This is good news," says researcher Lynn Rosenberg, ScD, professor of epidemiology at Boston University School of Public Health, in a news release. "The present study is definitive that hair relaxers don't cause breast cancer, as much as an epidemiologic study can be."

It's the first study to examine a potential link between chemical hair relaxers and breast cancer. Researchers say hair dye has been associated with an increased risk of certain types of cancer in some studies, but these results have not been conclusive.

Black women aged 45 or younger are more likely to develop breast cancer than white women of the same age, and black women of any age are more likely to die of the disease than white women.

But researchers say the increased risk among black women is not fully explained by known breast cancer risk factors, such as family history of the disease. Therefore, other potential causes of breast cancer among black women are currently under investigation.

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Hair Relaxers Not Cancerous

"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," says Rosenberg. "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."

Researchers say hair relaxers can enter the body through cuts or lesions in the scalp, but these products are not fully monitored by the FDA. Since manufacturers are not required to list all ingredients (some are considered to be trade secrets), they say there is the potential for harmful ingredients.

The study, published in Cancer Epidemiology Biomarkers & Prevention, followed nearly 50,000 African-American women who participated in the Black Women's Health study from 1997 to 2003.

During the study, 574 new cases of breast cancer were diagnosed, but researchers found no increases in breast cancer risk associated with duration of hair relaxer use, frequency of use, age at first use, number of burns experienced during use, or type of hair relaxer used.

This article was reviewed by Brunilda Nazario, MD.

SOURCES: Rosenberg, L. Cancer Epidemiology Biomarkers & Prevention, May 2007; vol 16: pp 1035-1037. News release, Boston University. News Release, American Association for Cancer Research.