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A young woman with no previous health issues experienced three consecutive episodes of acute kidney injury (AKI) following "Brazilian" hair-straightening procedures.

Though the 26-year-old Tunisian woman's kidney function quickly improved after each episode, she experienced scalp ulcers, vomiting, diarrhea, fever, and back pain, along with elevated plasma creatinine levels during each episode, reported Thomas Robert, MD, PhD, of Hôpital de la Conception in Marseille, France, and Emmanuel Letavernier, MD, PhD, of Sorbonne Université in Paris, in a case study published in the .

Each AKI episode coincided with a hair-straightening procedure at the same salon that used a cream containing 10% glyoxylic acid.

A relatively new product, glyoxylic acid was recently developed as a "seemingly safer alternative" to hair-straightening formulations that .

"It's worth noting the significance of glyoxylic acid in revolutionizing hair-straightening products by replacing formaldehyde, which is known to be toxic, particularly in its volatile state patented by a major pharmaceutical group," Robert and Letavernier told MedPage Today.

"Doctors need to think about this new potential cause of acute kidney injury, particularly if it occurs in a young woman, or if calcium oxalate crystals are present in a kidney biopsy with no cause found," they added.

The AKI episodes in the case study patient occurred in June 2020, April 2021, and July 2022. The woman's plasma creatinine spiked to around 2.0 mg/dL after each exposure to the hair-straightening cream and rapidly improved after each episode. At the last follow-up visit, plasma creatinine returned to normal at 0.78 mg/dL. Though no crystalluria or stone analyses were performed, urinalyses confirmed the presence of blood and leukocytes without proteinuria or infection. A CT scan showed no evidence of obstructive uropathy.

Similar cases have previously been who recently described 26 patients presenting with acute renal injuries after hair-straightening treatments at hair salons. Biopsies revealed the presence of calcium oxalate crystals in their kidneys. These researchers suspected an effect of glycolic acid, another substance found in many cosmetic products, including hair-straightening products. However, they were unable to provide conclusive evidence.

For the current case study, Robert, Letavernier, and their team applied the straightening product or a control cream -- in this case petroleum jelly -- to the backs of mice. The day after the cream application, urinalysis showed the presence of elongated calcium oxalate monohydrate crystals, like those observed after ethylene glycol intoxication, in the mice exposed to the glyoxylic-containing cream. Plasma creatinine level also significantly increased 28 hours after exposure to the straightening cream.

"The most remarkable finding we observed was the impact of applying this cream in mice, which induced severe oxalate nephropathy within 24 hours," Robert and Letavernier said.

Kidney 3D CT scans revealed the presence of dense tubule-molding calcium oxalate monohydrate deposits only in the mice exposed to the straightening cream.

"Interestingly, discussions with hairdressers revealed that although it is recommended not to apply this straightening product within 0.5 cm of the scalp, most clients request total smoothing effects," the authors noted. "This raises questions about the proportion of patients experiencing subclinical acute renal insufficiency episodes every 6 to 12 months, potentially contributing to the development of genuine chronic renal disease as a consequence."

"In view of their potential toxicity, cosmetic products containing glyoxylic acid should not be used anymore," they said.

Robert and Letavernier explained that following a European regulatory framework transposed in France in February 2013, cosmetic products like hair straighteners are no longer tested on animals. The FDA doesn't approve cosmetic products and ingredients, with the exception of color additives, prior to marketing.

"Given that there is no question of resuming animal testing in the cosmetics sector, it is essential to find new ways of detecting the possible toxic effects of products applied to the skin," they urged. "It would seem necessary to evaluate systemic passage and renal, hepatic, and cardiovascular toxicity, which is not currently done."

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