American scientists have found that the use of persistent dye and hair straighteners is associated with an increased risk of developing breast cancer in women. To do this, they analyzed data on more than 47 thousand American women, during the observation of 2794 of which were diagnosed with breast cancer. The risk of developing the disease was increased for both black and white women, and the reason for this connection may be in carcinogenic and hormonal substances used in cosmetics.

The main colouring material of persistent hair dye is initially colourless aromatic amines, which give the hair the desired colour after binding and oxidation. According to studies, some of the aromatic amines used in paints (for example, 4-aminobiphenyl ) are toxic and carcinogenic: taking into account the possible surface of contact with the substance (skin of the head or hands) and the use of volatile substances, using hair dye can, therefore, be potentially dangerous.

In particular, studies have previously shown a connection between hair dye and the risk of developing breast cancer, and the use of substances found in such dyes in experiments with laboratory animals even lead to the development of breast tumors in rats. Nevertheless, for an accurate conclusion about the dangers of hair dyes, large population studies are still not enough, which usually help to take into account and eliminate all the side variables that potentially affect the result.

Alexandra J. White from National Institute of Environmental Health Sciences and her colleagues decided to study the data collected during the Sister Study, a large-scale study of the causes of breast cancer in women aged 35 to 74 years. Participants in the project are almost 50 thousand women whose sisters were diagnosed with breast cancer: using a sister sample allows us to control genetic factors and environmental factors in such a way that we can reliably assess the influence of only individual factors – if breast cancer is diagnosed in the participants themselves.

A total of 47,650 women were in the sample. Each of them reported the use of dye and hair straighteners over the past 12 months: many of them contain derivatives of formaldehyde, a well-known carcinogen that is used to change and improve the mechanical properties of hair (in particular, straightening). The study took into account only the use of funds at home, women who worked in beauty salons were excluded from the sample. Of all the participants, 55 percent reported using persistent hair dye, and 9.9% reported using straighteners.

In addition, scientists also used data on the health of participants and their children, information on the onset of menopause and sociodemographic data. In particular, scientists paid special attention to the ethnos of the participants: it is believed that African Americans, because of their predominantly tough and highly curly hair of dark colour, often use hair straighteners and dyes, thereby exposing themselves to greater potential danger.

Over eight years of follow-up after the initial data collection, 2794 participants were diagnosed with breast cancer. Among women who used hair dye, the risk of developing breast cancer was higher: for black women – 45% higher, and for fair-skinned women – 7% higher. At the same time, the use of hair straighteners increased the risk of developing breast cancer by 18%, regardless of ethnicity. The risk of developing breast cancer significantly (p = 0.02) increased with an increase in the frequency of use of straighteners. There was also a relationship between the risk of developing breast cancer and the use of hair products on other people at home (the risk increased by about 28%).

The authors concluded that cosmetics for hair straightening and coloring play an important role in the development of breast cancer in women, significantly increasing the risk. Apparently, the aromatic amines that make up are not the only reason for this: the increased risk of developing breast cancer among African-American women is explained by the fact that, according to the results of toxicological studies, funds for black women contain more estrogen and endocrine disruptors. Of course, the scientists did not evaluate directly the composition of the means used and how much actually the substance got on the skin of the participants or in their respiratory tract – this will need to be done in additional studies.