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  • Previous studies have linked chemicals in some hair products to breast cancer.
  • New research has found hair straightening chemicals may increase risk of uterine cancer.
  • Risk was doubled for those frequently using hair straightening products compared to those not using them.
  • Uterine cancer is the fourth most common cancer among women in the US.

Various chemical ingredients are used in the formulation of hair products, many of which continue to be analyzed for their impacts on the body.

Now, new research conducted by the National Institutes of Health (NIH) and published in the Journal of the National Cancer Institute has found that chemicals included in some hair straightening products may increase the risk of developing uterine cancer.

The study assessed data spanning 11 years, relating to 33,497 US women aged 35-74. Insights were collected as part of the ongoing ‘Sister Study’ led by the National Institute of Environmental Health Science (NIEHS).

During this time, 378 women were diagnosed with uterine cancer. Those who frequently (four or more times per year) used hair straightening products had a 4.05% chance of developing the disease by age 70, compared to a 1.64% risk among women who did not use them.

Dr. Alexandra White, head of NIEHS’ Environment & Cancer Epidemiology Group and lead author of the study, revealed that, among women who used the products occasionally but less than four times per year, “we observed an elevated but not statistically significant small increase in risk.”

The team also explored the effects of hair dyes, bleaches, highlighters, and perms on the incidence of uterine cancer and found no association — which was somewhat unexpected.

“We were surprised to not see a higher risk for permanent dye use, which has been related to risk of other cancers, such as breast cancer,” stated White.

Diving deeper into the two-fold risk increase, the researchers noted that 60% of women in the study diagnosed with uterine cancer self-identified as Black.

They hypothesized this might be due to higher product use among this group.

“Black women are much more likely to report using these products, so the exposure burden is more pronounced for them,” White shared with Healthline.

So how does the level of use make a difference?

When chemicals enter our systems through the skin, they “do not stay in our bodies forever,” Dr. Kelly Johnson-Arbor, a medical toxicology physician and medical director at the National Capital Poison Center, revealed to Healthline.

“Chemicals that enter the human body are typically metabolized and excreted through the kidneys or feces, [and] people who are exposed to chemicals (including from hair straightener products) on a regular basis still metabolize and eliminate chemicals from their bodies.”

However, she continued, “using chemicals on a regular basis can result in a higher accumulation of chemicals in the body between exposures — which can lead to potentially dangerous health effects.”

The area to which chemicals are applied could also play a role in the absorption level, stated Dr. Ankit Madan, an oncologist with MedStar Health.

“The scalp, where hair straighteners are applied, may absorb more chemicals than other parts of the body,” he said.

Dr. Troy Gatcliffe, a gynecologic oncologist with Baptist Health Miami Cancer Institute, said, “there are myriad ways in which outside chemicals impact the body.”

He continued: “The most substantial way is the alterations in the genetic code of cells that can lead to cancerous growth.”

The researchers did not explore specific brands of hair straighteners, so were unable to pinpoint particular chemical ingredients. But they noted some of these products include:

  • Formaldehyde
  • Parabens
  • Metals
  • Phthalates
  • Bisphenol A

Formaldehyde and heavy metals (such as nickel, arsenic, and chromium) are types of carcinogens, and Johnson-Arbor revealed they have been associated with cancer development.

Meanwhile, phthalates, bisphenol A, and parabens “are classified as endocrine disrupting compounds, which means that they may affect fertility, puberty, and other hormone-sensitive body functions,” stated Johnson-Arbor. “They may also alter the balance of hormones within the human body.”

This is important because “excessive or inadequate hormone activity, including estrogen excess, can predispose individuals to certain diseases, including some cancers,” she added.

Despite not being as well known as some other types, uterine cancer — also known as endometrial cancer — is one of the most prevalent among women.

“Endometrial cancer develops in approximately 3% of females in the United States and is the fourth most common cancer in US females,” Dr. Melissa L. Torrey, director of the Breast Cancer Program at Redlands Community Hospital, revealed to Healthline.

While it’s most often seen in those aged 60-70, she continued, “2-5% of cases occur before age 40.”

Torrey explained that the uterus comprises three layers of tissue, and different cancers impact each of them. However, “adenocarcinoma of the endometrium is the most common site and type of uterine cancer,” she said.

The most common indicator of uterine cancer is unusual vaginal bleeding — which Torrey revealed is present in up to 90% of cases.

“Since the majority of the patients are older women who are post-menopausal, this presents typically as post-menopausal bleeding,” explained Madan.

For pre-menopausal women, he continued, it may present as bleeding in between periods or as heavy and frequent periods.

“I encourage women to be their greatest advocates and vocalize if they have any changes in their bleeding pattern or see any bleeding after menopause,” asserted Gatcliffe.

Aside from chemicals, there are a number of more widely-recognized uterine cancer risk factors.

According to Madan, these include:

Furthermore, although the researchers saw no difference in straightener use-related risk between races, they highlighted that the general prevalence of uterine cancer is rising faster among Black women.

“This is an area of active investigation,” said Gatcliffe. So why the disparity? A key contributor may be unequal access to health care, he explained — which can lead to less favorable diagnosis and treatment outcomes.

Interestingly, having multiple children (also known as parity) has been linked to reduced uterine cancer risk. However, Madan revealed a previous study found that “protection from parity was not seen in African-American women.”

According to Torrey, treatment options for uterine cancer depend on factors such as:

  • Type of tumor
  • Stage of disease
  • Grade of disease
  • Performance status of the patient

“The main treatment approach for uterine cancer includes non fertility-sparing staging hysterectomy,” revealed Gatcliffe. “[This] is when the uterus, ovaries, and tubes are removed, and nearby lymph nodes are checked.”

For younger patients, he added, “future fertility-sparing options, when appropriate, include oral high-dose progesterone therapies or progesterone-laden IUDs.”

In some instances of later-stage cancer, or when risk of recurrence is high, Torrey explained that radiotherapy or chemotherapy might also be used.

The prognosis varies according to the cancer’s stage.

Data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) program reveals that, with treatment, the 5-year survival rate for localized meaning cancer confirmed to the primary site is about 95%. If the disease spreads to the lymph nodes the 5 years survival rate is about 70%, if the cancer has metastasized the survival rate is about 18%.

The NIH study emphasized how chemicals in hair products may influence uterine cancer development. The same researchers previously found a link between permanent hair dyes and straighteners and breast cancer risk.

“This epidemiological evidence shouldn’t necessarily scare women to stop using straighteners altogether,” stated Gatcliffe, “but [it] provides evidence that they should be used with caution and under advisement.”

Further studies are required into the relationship between chemicals in hair products and cancers and their impact on different races. However, Madan stated, “this is an eye-opener.”