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Natural hair, not straightened Credit: Wikipedia

A number of hair styling products are actually harmful to health. This includes hair straighteners, which contain chemicals hazardous to both the hairdresser applying the products, as well as the woman that is using the product in her hair. These products are especially harmful if the woman using or applying the product is pregnant (it will go to the fetus) or breastfeeding (chemicals get into the mother's breastmilk).

A number of health risks are already known from chemicals (e.g., forever chemicals, formaldehyde) in such products, such as increased risks of certain cancers. But now there is an additional concern.

A  2024 study found that hair-straightening products containing glyoxylic acid was associated with a risk for acute kidney failure. This is because it resulted in the accumulation of calcium oxalate crystals in the kidneys. While the study was done on mice, the researchers thought this could explain cases of renal damage in young women. For example, one woman who became very ill with acute renal damage after each visit to a hair salon - where she had her hair straightened.

Similar cases have been noted elsewhere after women getting their hair straightened in hair salons. Black women are especially at risk because of their frequent use of such products. [Site with more information.]

According to the researchers, it is the glyoxylic acid that is problematic, but not glycolic acid.

Glyoxylic acid is found in some cosmetic products (such as shampoo, styling lotion, and straightening products) - generally as a replacement for formaldehyde (which is irritating and carcinogenic). However, glyoxylic acid is recommended to avoid contact with the scalp. (So why is it in the products!!??)

From Medscape: Hair-Straightening Products Entail Acute Kidney Failure Risk

The use of hair-straightening products containing glyoxylic acid is associated with a risk for acute kidney failure because of the accumulation of calcium oxalate crystals in the kidneys. The observation was made by a team of French researchers who tested the suspected straightening product on animals. The product is believed to be the cause of several episodes of renal damage in a young woman. ...continue reading "Hair Straighteners and Kidney Harm"

There has long been concern over the chemicals in hair dyes and chemical hair straighteners or relaxers, and whether they are linked to various cancers. Studies have had mixed findings with regard to breast cancer, but a review paper concluded that there is evidence to support a role of hair product use in the risk of early onset breast cancer, especially in African-American women. Other studies found that long term users of dark hair dyes have a significantly increased risk of non-Hodgkin's lymphoma, multiple myeloma, and bladder cancer. 

A recent study done in the New York City and New Jersey area looked at both African-American women and white women and their use of various hair chemical products. They found that regularly chemically relaxing hair or dying hair dark brown or black is associated with an elevated risk of breast cancer in both African-American and white women. And women using both types of products had an even higher risk of breast cancer.From Medscape:

Dark Hair Dye and Chemical Relaxers Linked to Breast Cancer

African-American and white women who regularly chemically straighten their hair or dye it dark brown or black have an elevated risk of breast cancer, new research suggests. The study of 4,285 African-American and white women was the first to find a significant increase in breast cancer risk among black women who used dark shades of hair dye and white women who used chemical relaxers.

Black women who reported using dark hair dye had a 51 percent increased risk of breast cancer compared to black women who did not, while white women who reported using chemical relaxers had a 74 percent increased risk of breast cancer, the study found. The risk of breast cancer was even higher for white women who regularly dyed their hair dark shades and also used chemical relaxers, and it more than doubled for white dual users compared to white women who used neither dark dye nor chemical straighteners.

The study included adult women from New York and New Jersey, surveyed from 2002 through 2008, who had been diagnosed with breast cancer, plus women of similar age and race but without a history of cancer.....While the vast majority - 88 percent - of blacks had used chemicals to relax their hair, only 5 percent of whites reported using relaxers. For dark hair dye, the numbers flipped, though the differences were not as dramatic. While 58 percent of whites said they regularly dyed their hair dark shades, only 30 percent of blacks did.

The most striking results showed increased risk in the minority of black women who used dark hair dye and white women who used chemical relaxers. Black women who used chemical straighteners and white women who used dark hair dyes were also at higher risk for breast cancer, but that might have been due to chance. James-Todd said that because so many of the black women used chemical relaxers and so many of the white women used dark hair dye, links would have been hard to detect. There’s no reason to believe that chemical relaxers and hair dyes would increase the risk for women of one race and not of another, she said. 

Previous studies have shown that long-term users of dark dyes have a four-fold increased risk of fatal non-Hodgkin’s lymphoma and fatal multiple myeloma, the authors write. Prior research also has associated dark hair dye use with an increased risk of bladder cancer. A 2016 report from the U.S. Centers for Disease Control and Prevention found that breast cancer rates are generally similar for black and white women, at around 122 new cases for every 100,000 women per year, although black women with the disease are more likely to die from it.  [Original study.]