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,” said study author Emmanuel Letavernier, MD, a nephrologist at Tenon Hospital in Paris. “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of glyoxylic acid through topical application, products containing this compound should be avoided and ideally withdrawn from the market, the researchers suggested in a letter published in The New England Journal of Medicine. The appropriate departments of the French Agency for Food, Environmental, and Occupational Health and Safety have been alerted, Dr. Letavernier added.
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 Dr. 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, Dr. 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.
A CT scan showed no signs of urinary tract obstruction. However, the patient had a small kidney stone. Further analysis revealed the presence of blood and leukocytes in the urine. But there was no proteinuria or urinary infection.
Chronic 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 Dr. 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.
“After passing through the epidermis, glyoxylic acid is rapidly converted in the blood to glyoxylate. In the liver and probably in other organs, glyoxylate is metabolized to become oxalate, which upon contact with calcium in the urine forms calcium oxalate crystals,” explained the specialist.
Excess calcium oxalate crystals causing renal failure are observed in rare conditions such as primary hyperoxaluria, a genetic disease affecting liver metabolism, or enteric hyperoxaluria, which is linked to increased intestinal permeability to oxalate: an anion naturally found in certain plants.
This story was translated from the Medscape French edition using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication. A version of this article appeared on Medscape.com.