Background <p>Acute interstitial nephritis (AIN) is a recognized cause of acute kidney injury (AKI), most commonly associated with medications. Increasing evidence also implicates exposure to environmental chemicals, including hair‑straightening products marketed as “formaldehyde‑free,” which may still contain or release nephrotoxic compounds. Reports have linked these products to oxalate nephropathy that may occur concurrently with interstitial nephritis, underscoring the need for awareness of their renal risks.</p> Case presentation <p>We describe a 26-year-old healthy woman who presented with nausea, vomiting, and bilateral flank pain three days after undergoing a professional hair-straightening treatment. Laboratory investigations revealed Stage 3 AKI with serum creatinine level 372 µmol/L, while serologic and infectious workup was unremarkable. Urinalysis showed leukocyturia, hematuria, and proteinuria. Kidney ultrasound was normal. Shortly after product application, the patient had experienced scalp pruritus and erythema. Kidney biopsy demonstrated mild mixed interstitial infiltrates with eosinophils, tubulitis, and rare intratubular oxalate crystals, consistent with acute hypersensitivity interstitial nephritis. Treatment with intravenous methylprednisolone followed by oral prednisolone resulted in clinical improvement and normalization of renal function within one month. Product review identified glycolic acid, a compound metabolized to oxalate, as a potential etiological factor.</p> Conclusion <p>This case illustrates severe AKI due to AIN with oxalate deposition following exposure to a hair-straightening product marketed as FA-free. Clinicians should maintain high suspicion for cosmetic exposures in patients with unexplained AKI. Awareness of these potential nephrotoxic effects is essential to support early recognition, appropriate management, and preventive public health measures.</p>