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.
"The results on mice are striking," study author Emmanuel Letavernier, MD, a nephrologist at Tenon Hospital in Paris, France, told the Medscape French edition. "They develop extremely severe acute kidney failure within 24 hours of applying the straightening cream. Samples show the presence of calcium oxalate crystals in all renal tubules."
Given the potential nephrotoxicity of glyoxylic acid through topical application, products containing this compound should be avoided and ideally withdrawn from the market, the researchers suggested in a letter published in The New England Journal of Medicine. ...
Replacing Formaldehyde
Glyoxylic acid has recently been introduced into certain cosmetic products (such as shampoo, styling lotion, and straightening products), often as a replacement for formaldehyde, which is irritating and possibly carcinogenic. Glyoxylic acid is praised for its smoothing qualities. However, it is recommended to avoid contact with the scalp.
Cases of renal complications could be underdiagnosed, according to the researchers, who are preparing a nationwide survey. Renal failure can be silent. Among the signs that should raise concern are "scalp irritation accompanied by nausea or vomiting after a hair salon visit," said Letavernier.
Similar cases have already been reported in the literature. An Israeli team recently described 26 patients treated for acute renal injuries after hair straightening in hair salons. Biopsies revealed calcium oxalate crystals in the kidneys.
The Israeli researchers suspected an effect of glycolic acid, another substance found in many cosmetic products, including straightening products. However, they could not provide evidence.
Glycolic Acid Safe?
By conducting a second animal study, which should be published soon, Letavernier and his team were able to rule out this hypothesis. "Glycolic acid does not pose a problem. Unlike glyoxylic acid, the application of glycolic acid on the skin of mice does not induce the formation of oxalate crystals in the kidneys, nor acute kidney failure."
The French clinical case reported in the correspondence concerns a 26-year-old woman with no prior health history who had three episodes of acute renal damage 1 year apart. It turned out that each episode occurred shortly after hair straightening at a hair salon in Marseille.
The patient reported feeling a burning sensation during the hair treatment. Scalp irritations appeared. She then experienced vomiting, diarrhea, fever, and back pain. Analyses revealed high levels of plasma creatinine during each episode, indicating renal failure.
After each episode, renal function rapidly improved. "The repetition of episodes of acute renal failure is, however, a major risk factor for developing chronic renal failure in the long term," said Letavernier.
The cream used in the hair salon to straighten hair was retrieved by the researchers. It contained a significant amount of glyoxylic acid but no glycolic acid.
To explore its potential nephrotoxic effect, they conducted a study on 10 mice. The animals were divided into two groups to test on one side topical application of the product and a gel without active product (control group) on the other.
Mice exposed to the product had oxalate crystals in their urine, unlike mice in the control group. A scan confirmed calcium oxalate deposits in the kidneys. Plasma creatinine levels increased significantly after exposure to glyoxylic acid.