A 20-year-old man in Taiwan went to a dermatology clinic with an itchy rash on his chest, neck and shoulders. Doctors found symmetric red bumps over a netlike pattern of darker skin. The best clue was not on his skin. It was on his plate: two months earlier, he had started a ketogenic diet.
The case, published in January 2026 in the New England Journal of Medicine, was diagnosed as prurigo pigmentosa, an uncommon inflammatory condition often nicknamed "keto rash." Despite the nickname, the rash appears tied to ketosis itself, whatever causes it, and it has been reported in people who were fasting, had diabetes, had undergone bariatric surgery, or had eating disorders.
