When Beauty Turns Toxic: Acute Contact Dermatitis and Kidney Injury Following Hair Straightening

The rising use of chemical hair straightening has led to an increase in adverse effects such as hair shaft fragility, allergic contact dermatitis and irritant contact dermatitis. These complications arise from repeated exposure to harsh chemicals, causing scalp damage and hair weakening. Long-term use can result in itching, burns, scarring, discoloration and hair loss [1]. We present a rare case of acute toxic contact dermatitis (ATCD), defined as an acute inflammatory skin reaction caused by the direct toxic effect of a chemical agent on the skin, without prior sensitization, complicated by acute renal failure following a hair straightening treatment [2]. We describe the case of a 25-year-old woman with no significant medical history who developed ATCD on her scalp after using a hair straightening product. She initially presented with pruritic erythema and desquamation on the scalp, followed 8 h post-application by epigastric pain, two episodes of diarrhoea, and eight episodes of vomiting. Additionally, the patient reported oliguria. On further questioning, the patient mentioned experiencing a burning sensation during the hair treatment. Physical examination demonstrated tenderness in the epigastric region. Dermatological assessment revealed erythematous, scaly plaques on the scalp, associated with dark crust formation (Figure 1). The renal workup revealed a significant elevation of creatinine at 160 μmol/L (previous baseline value: 62 μmol/L, 2 months earlier), without associated electrolyte disturbances, although renal ultrasound was unremarkable. Comprehensive workup excluded infectious, immunological, and haematological conditions. In the histological examination of a scalp skin biopsy, the epidermis exhibited keratinocytes that were alternately ballooned and showing signs of coagulative necrosis. The dermis displayed a few lymphocytes surrounding certain blood vessels (Figure 2). Renal biopsy demonstrated abundant microcrystalline calcium oxalate deposits with signs of acute tubular necrosis (ATN) (Figure 2C). The hair straightening cream, called ‘Lana’, a Brazilian product based on vegetable oil and enriched with five silk proteins, contained glyoxylic acid (GA), which may have contributed to the patient's skin reaction and renal complications. Experimental studies and clinical reports indicate that GA can be absorbed through the skin and metabolised into oxalate, potentially leading to the formation of calcium oxalate crystals in the kidneys and resulting in acute tubular necrosis. This mechanism is supported by renal biopsy findings showing calcium oxalate deposits in similar cases of hair-straightening–induced nephropathy [3, 4]. These findings are consistent with a diagnosis of ATN associated with acute kidney failure caused by GA exposure during hair straightening treatment. Intravenous hydration was initiated to support renal function. A complete recovery was noted within 2 weeks. Management of the scalp lesions included the application of a healing ointment and the use of a corticosteroid-based shampoo, and the patient was given a definitive injunction to avoid future use of the hair straightening product. Our case highlights a strong temporal and mechanistic link between exposure to the hair straightening product containing GA and the patient's acute kidney injury. The onset of renal symptoms occurred within hours of scalp application, and prior serum creatinine confirmed normal baseline renal function. Extensive workup excluded infectious, autoimmune, or hematologic causes, and no other nephrotoxic exposures were reported. Renal biopsy demonstrated abundant calcium oxalate deposits with acute tubular necrosis, consistent with oxalate nephropathy. GA is metabolised into oxalate, providing a biologically plausible mechanism for kidney injury. Recovery of renal function following cessation of exposure and supportive hydration further supports a causal relationship. These observations are consistent with previous experimental studies and clinical reports showing that GA can be absorbed through the skin and induce calcium oxalate–mediated nephropathy [3, 4]. Formaldehyde is a small, volatile molecule of the aldehyde family, well-known for its fixative and preservative properties. In some “keratin” hair-straightening treatments, it is used to cross-link hydrolyzed keratin to hair fibres, stabilizing the new shape [5]. Classified as a known human carcinogen by the National Toxicology Program, formaldehyde is present in some products, such as the Brazilian Blowout, at levels far exceeding the World Health Organization's recommended maximum concentration of 0.2% [6]. One study mentioned a level of 11% by weight, which creates a considerable health risk for users [7]. The occupational and consumer risks are substantial. Studies have shown that airborne formaldehyde concentrations can exceed established professional exposure limits, posing a health risk to both clients and, particularly, hairdressers who face repeated exposure [8]. Beyond formaldehyde, other compounds such as GA are frequently used and often marketed as a ‘formaldehyde-free’ alternative. However, GA and its derivatives (e.g., glyoxyloyl carbocysteine, glyoxyloyl keratin) are known to release formaldehyde when heated to high temperatures during the straightening process. These carbonyl compounds interact with hair keratin, modifying the hair's structure and compromising the integrity of its fibres. Furthermore, preliminary research suggests that percutaneous absorption of GA may contribute to acute kidney injury (AKI) [3, 4]. This case underlines the need to recognise GA as a possible cause of both cutaneous and renal complications from hair treatments, and highlights the importance of stronger regulation, further research, and greater awareness among professionals and consumers. The authors have nothing to report. Written informed consent was obtained from the patient to publish this report in accordance with the journal's patient consent policy. The authors declare no conflicts of interest. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.