Women who use permanent hair dye or chemical straighteners face a greater risk of breast cancer, scientists fear.
Researchers at the National Institutes of Health, a branch of the US Department of Health, tracked almost 50,000 women over eight years.
Women who reported regularly using permanent hair dye were nine per cent more likely to develop the disease, compared to those who hadn’t.
And those who had a chemical hair straitening treatment every five to eight weeks had a 30 per cent higher risk, results showed.
The researchers warn chemicals are able to get into the skin through the scalp. The fumes may also be inhaled while applying the dye.
They said that avoiding these chemicals ‘might be one more thing women can do to reduce their risk of breast cancer’.
Women who use permanent hair dye or chemical straighteners are more likely to get breast cancer, scientists have discovered
Over 5,000 chemicals are used in hair dye products, some of which are reported to be carcinogenic in animals, according to the National Cancer Institute.
It is not known whether some of the chemicals used in hair dyes today can directly cause cancer in humans. There is conflicting evidence.
Most studies on hair dye have not found an increased risk of breast cancer, but there is some evidence of a heightened risk of bladder and blood cancers.
This study, published in the International Journal of Cancer, suggests breast cancer risk increased with more frequent use of chemical hair products.
A person’s risk of developing cancer depends on how much, how long and how often a person is exposed to carcinogenic chemicals.
Data was taken from 46,709 women in the Sister Study, which tracks women across the US who give details about their health every year.
At the start of the study the women were asked about their use of hair dyes and chemical hair straighteners. The researchers then looked at who developed breast cancer at follow-up.
African American women who used permanent dyes every five to eight weeks had more have a 60 per increased risk of breast cancer.
In comparison, the risk was eight per cent among white women, according to the results published in the International Journal of Cancer.
This may be because hair products directed at African American have different chemicals or because they are more likely to use dark colour dyes – which have higher concentrations of chemicals.
However, there was little difference in risk among women who used chemical hair straighteners every five to eight weeks.
Chemical hair straightening – offered at most hair salons – is a permanent method of straightening hair or ‘relaxing’ curls that lasts a few weeks.
A mixture of chemicals is applied to the hair, including formulations in which the carcinogen formaldehyde is an active ingredient, the researchers said.
The researchers found little to no increase in breast cancer risk for semi-permanent or temporary dye use.
Dr Alexandra White, corresponding author, said: ‘Researchers have been studying the possible link between hair dye and cancer for a long time, but results have been inconsistent.
‘In our study, we see a higher breast cancer risk associated with hair dye use, and the effect is stronger in African American women, particularly those who are frequent users.’
Independent experts raised some limitations of the study which may mean the results do not apply to the general population.
Dr Michael Jones, of The Institute of Cancer Research, London, said: ‘Women were recruited to the study because they had a sister with breast cancer, so the conclusions wouldn’t necessarily hold true for women in the wider population, hence the need for further confirmation.
‘It’s also important to note that the authors weren’t able to look at the exact ingredients in the hair dyes and chemical straighteners.’
Professor Paul Pharoah, cancer epidemiology at University of Cambridge, said the findings are ‘quite likely’ to be a statistical fluke.
He called the results intriguing but said they do not offer good evidence that hair dyes or chemical straighteners raise the risk of cancer.
Professor Pharoah said: ‘Women who have used such products in the past should not be concerned about their risks.’
Co-author Dr Dale Sandler, chief of the NIEHS Epidemiology Branch, agreed that the results need to be replicated in bigger studies.
When asked if women should stop dying or straightening their hair, Dr Sandler said, ‘We are exposed to many things that could potentially contribute to breast cancer, and it is unlikely that any single factor explains a woman’s risk.
‘While it is too early to make a firm recommendation, avoiding these chemicals might be one more thing women can do to reduce their risk of breast cancer.’
WHAT EVIDENCE IS THERE THAT HAIR DYE CAUSES CANCER?
Researchers have been studying a possible link between hair dye use and cancer for many years with inconclusive results.
Some chemicals in hair dyes can be absorbed in small amounts through the skin or inhaled from fumes in the air.
Some of the ingredients used in hair dyes have been shown to cause cancer in lab animals, but it’s not clear how these results might relate to people’s use of hair dyes.
Although studies have shown that some of the dye applied to an animal’s skin is absorbed into the bloodstream, most have not found a link between skin application and cancer risk.
Some human studies show people who work around hair dyes regularly as part of their jobs, such as hairdressers, stylists, and barbers, are likely to be exposed more than people who just dye their hair on occasion.
A small but fairly consistent increased risk of bladder cancer have been found in people in those jobs, and findings have been mixed for studies into leukemias and lymphomas, the American Cancer Society says.
The International Agency for Research on Cancer (IARC) has concluded that workplace exposure as a hairdresser or barber is ‘probably carcinogenic to humans,’ based on the data regarding bladder cancer.
The National Toxicology Program (NTP), formed from parts of several different US government agencies, has not classified exposure to hair dyes as to its potential to cause cancer. However, it has classified some chemicals that are or were used in hair dyes as ‘reasonably anticipated to be human carcinogens’.