Is glyoxylic acid used in Brazilian straightening treatments dangerous?

Acute kidney failure is a common condition affecting approximately 8.3% of outpatient patients and up to 32% of hospitalised individuals. It presents with abdominal or lower back pain, nausea and vomiting, and requires immediate hospitalisation for dialysis. Unlike chronic kidney failure, acute kidney failure refers to a temporary and reversible kidney dysfunction, caused by haemorrhage, sepsis, drug poisoning or urinary tract obstruction. Another factor has recently been suspected: Brazilian smoothing products containing glyoxylic acid.

These haircare products had already been implicated in a report published in 2023, which listed 26 patients treated in 14 medical centres in Israel between 2019 and 2022 for acute kidney failure. All these hospitalisations followed exposure to Brazilian smoothing products. Among these patients, seven (26%) underwent kidney biopsies, revealing intratubular deposits of calcium oxalate in six of them, suggesting a potential link with exposure to glyoxylic acid.

Following the introduction of glyoxylic acid into the bloodstream, it is metabolised into oxalic acid by the enzyme lactate dehydrogenase, found in the cytoplasm of liver cells (hepatocytes). At a physiological pH of 7.4, the oxalic acid then dissociates to form oxalate ions, which can precipitate as calcium oxalate crystals in the renal tissues, compounds that damage the kidneys.

The toxicity of glyoxylic acid and its ability to penetrate the skin barrier were notably highlighted in a recent study conducted on rats. Four groups of five rats were formed, on which various creams were tested: a Brazilian smoothing product containing, among other things, 10% glyoxylic acid, a cream containing 10% glyoxylic acid, another cream containing 10% glycolic acid, an active ingredient sometimes accused of having the same level of danger as glyoxylic acid, and a control cream.

Scientists have observed that the applications of cream containing glyoxylic acid and the hair straightening product have significantly increased urinary oxalate excretion and caused a calcium oxalate nephropathy after transcutaneous absorption, unlike glycolic acid and the control. These increases are visible in the figure below in the "Urine oxalate" and "COM crystals in urine" histograms, the latter referring to the concentration of calcium oxalate crystals present in the urine. It is indeed interesting to note that these crystals are only present in the rats from the "hair straightening product" and "10% glyoxylic acid cream" groups, which seems to confirm the theory that this active ingredient penetrates the skin before reaching the kidneys.

Furthermore, an increase of approximately 80% in plasma creatinine, a chemical waste product produced by muscle metabolism, was detected for the "hair straightening product" and "10% glyoxylic acid cream" groups. This is shown by the "Plasma creatinine" histogram in the figure above. The measurement of urinary or blood creatinine is commonly used to assess kidney function and an increase in this waste product indicates that kidney function has been impaired. Conversely, the applications of the control cream and the 10% glycolic acid cream had no impact on kidney function.

Scientists also conducted a computed tomography (CT-scan) of the kidneys. The areas highly concentrated in calcium oxalate crystals appear in red. The three CT-scans performed are in agreement with the histogram results and show a significant concentration of oxalate crystals in the kidneys of the rats from the "hair straightening product" and "10% glyoxylic acid cream" groups, unlike those in the "10% glycolic acid cream" group. The presence of oxalate crystals in the kidneys of the rats from the "10% glyoxylic acid cream" group was confirmed by Yasue staining, the small black dots visible in the figure above revealing the crystals.

Even though correlations appear to exist between the use of glyoxylic acid and an increased risk of acute kidney failure, it is important to exercise caution as several limitations remain.

Indeed, the aforementioned study is based on groups of only five rats, a sample size too small to establish robust conclusions applicable to humans. On the other hand, the number of reported cases of individuals experiencing acute kidney failure following a Brazilian blowout is extremely low considering the popularity of this practice, used by millions of people for decades, with no similar precedents until the last five years. This relatively recent timeframe prompts questioning: environmental factors, lifestyle changes, or even individual characteristics of the patients could play a role and warrant thorough investigation. Studies with larger sample sizes and rigorous follow-up are necessary to clarify the link between glyoxylic acid and the rare cases of reported acute kidney failure.

Whilst we await the comprehensive investigations that ANSES plans to conduct to confirm or refute the link between the use of glyoxylic acid and an increased risk of acute kidney failure, it is recommended, as a precautionary principle, to avoid Brazilian hair straightening treatments. If symptoms suggestive of acute kidney failure appear after a Brazilian hair straightening treatment, promptly consult a doctor, specifying the context of their onset.