A Supposedly Safer Hair-Straightening Ingredient Could Be Damaging People’s Kidneys

A woman’s hair care routine seems to have given her repeated bouts of kidney damage. In a new case study this month, her doctors describe how the woman’s use of hair-straightening products containing a certain ingredient likely injured her kidneys. The ingredient, called glyoxylic acid, has been tied to similar incidents in the past and the authors argue that its inclusion in these products should possibly be discontinued.

The case was detailed earlier this month in the New England Journal of Medicine. According to the report, the 26-year-old woman began to experience episodes of back pain, fever, vomiting, and diarrhea on days that she received hair-straightening treatments at a salon. She also reported feeling a burning sensation on her head following the treatments, which caused actual ulcers to form on the scalp. The symptoms recurred during three visits she made to the salon between 2020 to 2022 and dissipated quickly thereafter. And she reported being treated with a straightening cream that contained glyoxylic acid at each appointment.

The doctors’ medical tests on the woman detected lingering signs of kidney injury, such as increased creatinine levels and blood in her urine. But she didn’t seem to have an infection or other known causes of acute kidney damage, such as blockages along her urinary tract. Given the timing of the woman’s symptoms and the lack of any other explanations, the doctors say that her exposure to glyoxylic acid was the most likely culprit. But they went one step further to be sure, conducting experiments with mice.

The authors exposed the backs of some mice to the very same product used on the woman and compared them to a control group (these mice were merely smeared in petroleum jelly). The next day, tests found higher levels of creatinine in the treated mice compared to controls. And only the exposed mice had “elongated” crystals of a chemical known as calcium oxalate monohydrate in their urine as well as deposits of calcium oxalate monohydrate inside their kidneys.

Based on these experiments and other evidence, the authors concluded that the glyoxylic acid in the product was absorbed through the woman’s skin, eventually reaching the kidneys. The breakdown of glyoxylic acid then led to the formation of sharp enough calcium oxalate crystals to damage the kidney.

The authors’ findings have “demonstrated convincingly” that applying hair straightening creams containing glyoxylic acid topically, that is, externally, “can cause kidney damage,” Joshua David King, an associate professor of medicine and pharmacy at the University of Maryland not affiliated with the research, told Live Science.

Interestingly enough, glyoxylic acid and similar chemicals are intended to be safer alternatives to formaldehyde, which has long been used in hair-straightening products but is now being phased out in many countries over concerns of its short and long-term toxicity, including a possible increased risk of cancer (the U.S. is expected to formalize a ban by next year). But this case study is only the latest piece of evidence to link these supposedly safer products to the risk of kidney damage.

While the woman’s symptoms were short-lasting, the authors say their case should serve as a warning about the possible risks of glyoxylic acid in hair-straightening products and that such products might need to be avoided or even “discontinued from the market.”