A weird, itchy rash is linked to the keto diet—but no one knows why

A 20-year-old man from Taiwan sought help at a dermatology clinic due to an unusual rash that had appeared on his shoulders and chest. For an entire month, he struggled with this raised, red, and itchy condition, which eventually led to patches of pigmented skin mixed with the inflamed areas. According to a case report published in the New England Journal of Medicine, a biopsy revealed swelling between skin cells and inflammation surrounding blood vessels. However, tests for other common skin conditions returned negative results, leaving the medical team with limited options for diagnosis. The breakthrough came when the patient revealed a significant change in his lifestyle: he had adopted a ketogenic diet just two months prior to his visit, coinciding with the onset of his rash. The ketogenic diet is characterized by high fat and very low carbohydrate intake, prompting the body to transition from using glucose as its primary energy source to relying on fat. This metabolic shift, known as ketosis, involves the breakdown of fat tissue, releasing free fatty acids that are transported to the liver for conversion into acetyl-CoA. An excess of this molecule can disrupt metabolic processes and lead to the production of ketone bodies, primarily acetoacetate and beta-hydroxybutyrate. Ketone bodies, once formed in the liver, enter the bloodstream and serve as an energy source for various tissues, especially the brain. While ketogenic diets have established clinical applications—especially in managing drug-resistant epilepsy and certain genetic metabolic disorders—interest is growing in their potential benefits for obesity, type 2 diabetes, and even neurodegenerative diseases like Parkinson’s and Alzheimer’s.