Hair Dyes, Other Hair Products, and Cancer Risk
Why is there concern that hair dyes may cause cancer?
Hair dyes use chemicals to change the color of the hair. There are three main types of hair dye: permanent, semi-permanent, and temporary.
Permanent hair dyes, which make up about 80% of currently marketed hair dye products, use colorless dye intermediates and dye couplers. In the presence of hydrogen peroxide, the intermediates and couplers react with one another to form pigment molecules. Darker colors are formed by using higher concentrations of intermediates.
The other types of hair dyes, known as semi-permanent and temporary hair dyes, do not involve such chemical reactions. Instead, they include colored compounds that stain hair directly.
Some of the chemicals in hair dye products have been reported to be carcinogenic (cancer-causing) (1, 2). These include aromatic amines, which were used as dye intermediates in early permanent hair dye formulations.
In the mid- to late 1970s, manufacturers changed the components in permanent hair dye products to eliminate some of the carcinogenic chemicals used as dye intermediates (1, 3, 4). It is not known whether any of the chemicals still used in hair dyes are carcinogenic (5).
People who use hair dyes frequently as part of their job, such as professional hairdressers, likely have higher exposures to potentially harmful chemicals in these products than people who have their hair dyed in a salon or who dye it at home (that is, “personal users” of hair dye). Thus, studies have been conducted to understand both exposure to hair dyes in the occupational setting and exposure from personal use.
It has been estimated that between 50% and 80% of women in the United States, Japan, and the European Union have used hair dyes (6). Given the widespread use of hair dye products, if these products had even a small effect on cancer risk that could translate into a considerable public health impact.
Do hairdressers and barbers have an increased risk of cancer?
In 2010, a report from the International Agency for Research on Cancer (IARC) concluded that some of the chemicals professional hairdressers are exposed to are “probably carcinogenic to humans” (6). This conclusion is based on many studies that have found an increased risk of bladder cancer in hairdressers and barbers who were occupationally exposed to hair dye (1, 7). A 2010 meta-analysis of 42 studies found that the longer someone had worked as a hairdresser, the more likely they were to have developed bladder cancer. Those who had been hairdressers for at least 10 years were nearly twice as likely to develop bladder cancer as those who had never worked as a hairdresser (7).
One study looked at risks among Swedish hairdressers over different time periods. That study found no increased risk in recent decades, suggesting that professional use of modern hair dyes, which no longer contain aromatic amines, may not be associated with bladder cancer risk (8).
Do people who have their hair dyed have increased risks of cancer?
Epidemiologic studies that follow groups of people over time (cohort studies) or that study people with and without specific cancers (case–control studies) have examined possible associations between personal use of hair dyes and risks of several cancers. Based on a review of existing evidence, the IARC Working Group considers personal use of hair dyes overall as “not classifiable as to its carcinogenicity to humans” (6).
Bladder cancer. A 2014 analysis of data pooled from 17 studies found no evidence of an increased risk of bladder cancer associated with personal hair dye use (9). However, for personal use of permanent hair dyes specifically, the evidence of an association with bladder cancer is mixed. Some studies (10–12) found no association, whereas others found an association in specific subgroups of users (13–15).
Non-Hodgkin lymphoma. A number of studies have investigated the relationship between personal use of hair dyes and the risk of non-Hodgkin lymphoma (NHL), with conflicting results. A pooled (combined) analysis of four case–control studies found that women who began using hair dye before 1980 (before formulations were changed to remove carcinogenic compounds) were 1.3 times as likely to develop NHL as women who had never used hair dye, whereas no increase in risk was seen for women who began using hair dye after 1980 (16). A large 2020 prospective cohort study reported no association between personal use of hair dye and the risk of non-Hodgkin lymphoma (12).
Breast cancer. Many studies have examined possible associations between hair dye use and breast cancer, with mixed and inconsistent results. However, more recent studies that have looked at larger populations of women with longer follow-up periods and more detailed characterization of hair dyes and other breast cancer risk factors have found that certain kinds of exposures may be associated with risk.
For example, a large US cohort study that included mostly White women reported an increased risk of breast cancer overall, and of hormone receptor–negative breast cancers, with increasing exposure to hair dye (12). Another prospective study of US women who used dark or permanent hair dyes found that risks of breast cancer were higher in those who reported any use of hair dye than in those who reported no use (17). When the authors analyzed the data by racial group, they found that among non-Hispanic White women, hair dye users were 1.07 times as likely to develop breast cancer as non users, and among Black women users were 1.45 times as likely to develop breast cancer as nonusers (17).
Other cancers. Although some individual studies have shown associations between hair dye use and the risk of leukemia, a meta-analysis of 20 studies showed a small association that was not statistically significant (19). In addition, a large cohort study found no association between ever use of hair dye and the risk of leukemia but very slightly increased risks of basal cell carcinoma (particularly in women with naturally light hair) and ovarian cancer (12).
Do people who use hair straighteners or relaxers have increased risks of cancer?
Treatments used to straighten or relax hair contain a mixture of chemicals. Some formulations contain the carcinogen formaldehyde as an active ingredient. Several studies have found associations between the use of hair straighteners or relaxers and the subsequent development of breast cancer.
- In a large case–control study in New York and New Jersey, White women who had ever used chemical hair relaxers were 1.7 times as likely as nonusers to develop breast cancer (20), but no such association was seen in Black women.
- In another large case–control study, Ghanaian women who had ever used these products were 1.6 times as likely as nonusers to develop breast cancer (21).
- A large prospective study in the US found that women who used hair straighteners at least once per month in the previous 12 months were 1.3 times as likely to develop breast cancer as nonusers (17). In that same cohort of women, frequent use of straighteners and perms during adolescence was associated with a higher risk of premenopausal breast cancer (22).
- A nationwide prospective study of Black women found evidence that heavy users of lye-containing hair relaxers were more likely to develop estrogen receptor–positive breast cancers than never or light users (23).
Recently, a large cohort study found that women who had used any straightening products in the previous 12 months had 1.8 times the risk of developing uterine cancer as those who had never used such a product (24).
Because hair straighteners and relaxers contain varying compositions of chemicals, future studies will try to narrow down which chemicals have specific health impacts.