Prurigo pigmentosa (PP) is probably underdiagnosed due to lack of awareness. Previously, it was assumed that PP primarily affected Japanese females; however, more cases are reported worldwide, and the pathogenesis is still not completely understood. In this case report, we present two healthy Danish siblings, who developed PP approximately 2 weeks after starting a ketogenic diet, suggesting that both increased levels of ketone bodies in the blood together with a genetic predisposition might play a role in the development of PP.