In the hunt for the causes of breast cancer, Rutgers researchers say they may have found two new possible culprits: Hair dyes and relaxers.
More specifically, darker shades of hair dye.
The possible association between commonly used hair products and the most frequently diagnosed cancer for women came to light in a close look at 4,285 women in New Jersey and New York who have been diagnosed with some form of breast cancer.
The study revealed a different effect based on race.
The women were asked about their use of hair dyes and relaxers - what shade they used, how often they used it, and for how long. It is the first study to take a look at the impact of relaxer products on Caucasian women, said study lead author Adana Llanos, an epidemiologist with Rutgers Cancer Institute of New Jersey and Rutgers School of Public Health.
The study found:
- For African-American women, a 51 percent increased risk of developing breast cancer among those women who used dark brown or black hair dye (It found no comparable jump for Caucasian women)
- Also for African-American women, a 72 percent increase in the type of breast cancer known as estrogen-positive among those who used dark brown or black dye.
- For Caucasian women, a 74 percent increased risk for those who used chemical relaxers or straighteners.
In addition, the association between hair dyes and cancer was higher - or riskier, in other words - for salon dyes compared to home kits.
The study appears in the June 2017 online issue of Carcinogenesis.
Llanos was quick to caution her study doesn't "prove" these hair products cause cancer. It's simply too soon to tell, and more research would have to take a closer look to reach such a conclusion, she said.
"Just because we found these associations doesn't mean that if you dye your hair dark, or any color, you're going to get breast cancer," Llanos said. "But at the same time, the study points to something else we should be mindful of."
The study didn't ask the women what brands of products they used, so researchers weren't able to look for links between cancer and specific ingredients.
Because of the marked increase in estrogen-positive cancers, it is thought the dyes either contain chemical compounds that mimic estrogen, or trigger a change in the body that somehow triggers the production of estrogen.
"There must be some role for estrogen, for sure," Llanos said. "That's why we're seeing the differences."
The effect would be indirect, however, in a way that wouldn't be evident to the consumer reading the package label. "If you look at the ingredients, it's not going to say, 'estrogen,'" she said.
The use of hair products varied tremendously by race: 88 percent of African-American women used relaxers, while only 5 percent of white women did. For hair dyes, however, 58 percent of the women in the studied dyed their hair, while only 38 percent of the African-Americans did.
Researchers took into account all the other known factors that could skew the results: family health history, reproductive history, hormone use, tobacco use, alcohol consumption, physical activity, and vitamin use.
Study subjects in New Jersey came from 10 counties: Bergen, Burlington, Camden, Essex, Hudson, Mercer, Middlesex, Monmouth, Passaic, and Union.
Kathleen O'Brien may be reached at kobrien@njadvancemedia.com. Follow her on Twitter @OBrienLedger. Find NJ.com on Facebook.