NEJM: Some Hair Straightening Products May Cause Kidney Injury

Thomas Robert, MD, AIXAssociate Professor of Nephrology APHM (Assistance Publique - Hopitaux de Marseille) Marseille, Provence-Alpes-Côte d'Azur, France 

Dr. Thomas Robert Interview with:
Thomas Robert, MD, AIX
Associate Professor of Nephrology
APHM (Assistance Publique – Hopitaux de Marseille)
Marseille, Provence-Alpes-Côte d’Azur, France


Prof. Emmanuel Letavernier, MD PhDNephrologist at Tenon Hospital Paris, France

Dr. Letavernier

Prof. Emmanuel Letavernier
, MD PhD
Nephrologist at Tenon Hospital
Paris, France What is the background for this study?

Response: Our work was prompted by emerging concerns surrounding the potential nephrotoxic effects of hair-straightening products containing glyoxylic acid. This inquiry was instigated by a patient who experienced three repeated acute episodes of kidney injury in June 2020, April 2021, and July 2022, each occurring shortly after a hair-straightening procedure. Notably, these episodes resolved with hydration.

Upon examining the composition of the hair product used by the patient, which contained glyoxylic acid, and considering the patient’s report of  painful ulcer scalp during application and subsequent scalp scarring, we suspected a potential link between exposure to glyoxylic acid and kidney injury. Consulting with my colleague, Professor Emmanuel Letavenier, a specialist in crystalline nephropathy at Paris, confirmed this suspicion.

In summer 2023, cases series have been reported by an Israeli team (, who described 26 patients presenting with acute renal injuries after hair straightening treatments. Biopsies revealed calcium oxalate crystals in the kidneys. The Israeli researchers suspected an effect of formaldehyde and glycolic acid, another substance found in many cosmetic products, including hair straightening products, but were unable to provide conclusive evidence. What are the main findings?

Response:  We decided to initiate experimental investigations hair straightening product use by the hair salon for this patient. We applied either the straightening product or a control cream (petroleum jelly) to the backs of mice. Urinalysis conducted the day after application showed the presence of elongated calcium oxalate monohydrate crystals in mice exposed to the glyoxylic-containing cream, sharing similarities with those observed after ethylene glycol intoxication. Additionally, plasma creatinine levels 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. Kidney 3D CT scans revealed the presence of dense tubule-moldering calcium oxalate monohydrate deposits only in the mice exposed to the straightening cream.

We hypothesize that after penetrating the epidermis, glyoxylic acid is rapidly transformed into glyoxylate in the blood. In the liver and possibly other organs, glyoxylate is metabolized to oxalate, which, upon contact with urine calcium, forms calcium oxalate crystals.

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. This raises questions about the proportion of patients experiencing subclinical acute renal insufficiency episodes every six to 12 months, potentially contributing to the development of genuine chronic renal disease as a consequence.

It is intriguing to consider that glyoxylic acid, a relatively new product, was recently developed as a “seemingly safer alternative” to hair straightening formulations containing formaldehyde. What should readers take away from your report?

Response: It is crucial for readers to recognize the potential risks associated with the use of hair-straightening products containing glyoxylic acid. Our study underscores the importance of informed decision-making when selecting personal care products, particularly those with chemical ingredients. Following a European regulatory framework transposed in France since February 2013, cosmetic products like hair straighteners are no longer tested on animals. Additionally, the FDA doesn’t approve cosmetic products and ingredients, with the exception of color additives, prior to marketing What recommendations do you have for future research as a results of this study?

Response: In light of our findings, “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.” Additionally, there is a need for regulatory agencies to evaluate the safety profile of hair-straightening products and consider implementing stricter guidelines to protect public health. Is there anything else you would like to add?

Response: Additional Comments and Disclosures:

We would like to emphasize the importance of collaboration between healthcare professionals, researchers, industry stakeholders, and regulatory authorities to address the safety concerns surrounding hair-straightening products containing glyoxylic acid. Our study was self-supported, and we declare no conflicts of interest.

Citation: New England Journal of Medicine

Robert T, et al “Kidney injury and hair-straightening products containing glyoxylic acid” N Engl J Med 2024;
DOI: 10.1056/NEJMc2400528.


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Last Updated on March 28, 2024 by Marie Benz MD FAAD