Hair straightening products increase the risk of endometrial cancer

Products used to straighten hair increase the risk of endometrial cancer, according to a new study from the US National Institutes of Health (NIH).

The findings, published in the Journal of the National Cancer Institute, are especially relevant to black women, who make up the majority of straightening product users in the United States.

According to work data, women who use these products frequently, more than four times a year, are twice as likely to develop this type of tumour in the uterus, endometrial cancer, which should not be confused with uterine cancer.

Similar associations were not found for other hair products, such as dyes, bleaches, highlights, or perms.

Hair straightening products increase risk of cancer

"We estimate that 1.64% of women who have never used a hair straightening product will have developed uterine cancer by the age of 70, but for frequent users, this risk increases to 4.05%," said Alexandra White, Ph.D., head of the NIEHS Environment and Cancer Epidemiology group and lead author on the new study.

"The doubling of this rate is concerning," she said. Still, "it's important to put this information in context: uterine cancer is a relatively rare type of cancer," she added.

"Endometrial cancer is the second most common gynaecological tumour in the world," explains Laura Costas, a researcher at the Molecular Epidemiology and Genetics in Infections and Cancer Unit of the Catalan Institute of Oncology (ICO).

"It is not a rare tumour," says the researcher who, however, asks that the results of the investigation be taken with caution. "This is the first study to issue this warning about hair straightening treatments." Before setting off the alarms, she continues, "you have to replicate the investigation to see if the tests are consistent or not," stresses.

Study followed 33,500 women

The study has followed about 33,500 American women for nearly 11 years. Sixty per cent of the women in the study who reported using hair-straightening products in the past year identified themselves as black, a population in which endometrial cancer rates have risen in recent years.

Since black women use hair straightening products more often and tend to start younger, "these results could be particularly interesting for them," said study co-author Che-Jung Chang.

The findings of this study add to previous work by this research group that had already indicated that straightening treatments could increase the risk of hormone-related tumours in women. Thus, other studies have already established a link between relaxants and an increased risk of breast cancer.

Chemical used in these products

The researchers did not collect data on the brands or ingredients of the hair products used by the women in the study. However, in their conclusions, they point out that different types of chemical substances commonly used in these products (such as parabens, bisphenol A, metals and formaldehyde) could have contributed to the observed increased risk. Exposure to these chemicals through hair treatments may be more of a concern than other sources of exposure, as absorption through the scalp may be greater, they note.

At the time the practices of the women included in the study were analyzed, a period between 2003 and 2009, a keratin treatment known as "Brazilian straightening" was popular for straightening. Subsequently, its use has decreased.

In any case, Costas, an expert in the epidemiology of endometrial cancer, points out that previous studies that have analyzed the influence of disruptors such as bisphenol A or formaldehyde in this type of tumour have not found the existence of an association.

"Further research is needed to confirm these results in different populations to determine whether hair treatments contribute to the observed disparities in uterine cancer and to identify whether there are specific chemicals that might increase cancer risk in women," they acknowledge.

Endometrial cancer risk

The risk factors for the development of endometrial cancer that is known at the moment explains Costas, are hormonal factors, exposure to estrogen or obesity, in addition to a hereditary component that has been identified.

Generally, this type of tumour has a good prognosis when detected early, although it is sometimes necessary to remove the uterus.

The main symptom of the disease is the appearance of hormonal bleeding, usually postmenopausal.

With the new data in hand, "the most prudent thing is not to expose yourself too much to these straighteners, but always bearing in mind that the evidence is not definitive and more studies are necessary to confirm the data," concludes Costas.

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