Formaldehyde-free hair-straightening products are hair-smoothening solutions widely used by professional beauty salons. Formaldehyde-free hair straighteners do not technically contain formaldehyde; however, they contain other chemicals such as glyoxyloyl carbocysteine which releases formaldehyde upon contact with heat. Moreover, its by-product glyoxylate may convert to oxalate; both compounds have potential nephrotoxic effect. Here, we report a case of a 41-year-old woman who presented to the emergency room with weakness, nausea, vomiting, and stage 3 acute kidney injury (AKI) according to Kidney Disease: Improving Global Outcomes (KDIGO) acute kidney injury staging shortly after exposure to formaldehyde-free hair-straightening product; other causes of AKI were excluded such as preceding acute illness, drug history, or other nephrotoxic agent exposure. On physical examination, the patient was pale, and her vital signs were normal. The urine microscopy and serologic workup were not indicative. Kidney core biopsy revealed interstitial edema, acute interstitial nephritis, and oxalate crystal nephropathy. Kidney function completely recovered after a short course of steroid therapy. In this case, AKI was a complication caused by exposure to hair-straightening products branded as formaldehyde free but actually containing other chemical products which release formaldehyde and other toxic chemicals when heated during the straightening procedure and may cause systemic toxicity, particularly kidney injury. Different cosmetic products are widely in use, but not all are under tight regulation, and therefore, it is important to raise the awareness among both medical teams and consumers of possible adverse health effects of different cosmetic products.