A new large population study looks to clarify the theorised connection between hair dye and cancer. The study found no link between ever using hair dye and an increased risk of most types of cancer in women. However, it did find a possible relationship between hair dye and certain forms of breast cancer, ovarian cancer, and the most common kind of skin cancer — links that “warrant further investigation.”
The study, published in the BMJ this week, looked at data from another research project, called the Nurses’ Health Study. That study has kept track of volunteers’ health and lifestyle habits since 1976, with questionnaires sent out and returned every two or four years. More than 120,000 women between the ages of 30 to 55 were initially enrolled.
The researchers of this study looked at 117,200 women who detailed whether or not they had ever used permanent hair dye and were reported free of cancer at the start of the project. On average, the women were followed for 36 years, and a third reported hair dye use at some point in their lives. During that time, there were more than 47,000 self-reported cases of cancer among the women, along with over 4,800 deaths.
The study found no significant association between a greater chance of most cancers and hair dye use, regardless of how long or often the women used hair dye. It also found no link between a greater risk of dying from cancer and hair dye use.
Compared to women with no hair dye use, however, women who had ever used hair dye did seem to have a higher risk of developing hormone receptor-negative breast cancer, a form of breast cancer that tends to grow faster, affects younger women, and doesn’t respond to treatments that block or lower the hormone estrogen and progesterone. They also had a higher associated risk of ovarian cancer and basal cell carcinoma, the most common but very treatable form of skin cancer.
The results of this new study agree with other research showing no link between hair dye and many types of cancer, including a 1994 study using the same group of women that ruled out a hair dye link to leukemia and related blood cancers. But it also lines up with recent research tying breast cancer, specifically, to hair dye use. That includes a government-led study last December that found such a link, which was even greater for Black women in particular.
“This prospective cohort study among mostly white U.S. women offers some reassurance against concerns that personal use of permanent hair dyes might be associated with increased cancer risk or mortality,” the authors wrote. “However, we did find a positive association for risk of some cancers.”
Cancer risk often is a very hard thing to study and nail down. There are around 5,000 chemicals that are found in hair dye products and some are known to be carcinogenic on their own. But the risk of any one thing causing cancer can be affected by a lot of factors, including a person’s genetics, environment and the strength of exposure to it. Another unanswered question is how much added risk hair dye might come with, assuming it does exist.
The World Health Organisation has found that the occupational exposure of hair dye faced by people working all day in salons and similar places, for instance, is a probable human carcinogen. The personal use of hair dye, however, is currently considered what the WHO calls a “group 3 agent,” meaning there’s not enough evidence to classify its cancer risk either way right now.
These sorts of studies alone can’t directly prove or disprove a causative link to cancer. But they do give scientists a clearer direction to focus on, such as the cancers that may have been associated with hair dye use in the study. Importantly, the authors note, future studies should look at more diverse groups of women and look outside of the U.S. as well as take into account the type of colour dye they were using, something that wasn’t possible in this study. Darker hair dyes are especially of concern to study, the authors noted, since they tend to contain more chemicals than lighter ones.
The American Cancer Society, discussing the research on hair dye and cancer so far, summarises things well:
“It’s not clear how much personal hair dye use might raise cancer risk, if at all. Most studies done so far have not found a strong link, but more studies are needed to help clarify this issue.”