Pellagra is a serious disease caused by not getting enough niacin, a vitamin (also called vitamin B3) that your body needs to turn food into energy and keep your skin, digestive system, and brain healthy. People with pellagra develop rough, scaly skin (especially where the sun hits), suffer from diarrhea, feel confused or forgetful, and become very weak. If left untreated, pellagra can be fatal.

This disease became common in the American South in the early 1900s, where many poor families ate mostly corn and almost nothing else. Doctors didn't understand what caused it until Dr. Joseph Goldberger proved in 1915 that pellagra came from diet, not germs. He showed that people who ate meat, milk, and vegetables didn't get sick, while those eating only cornmeal and molasses did. His discovery was controversial because many doctors refused to believe that a disease could come from what you ate rather than from infection.

The name comes from Italian words meaning “rough skin,” which describes one of its most visible symptoms. Today pellagra is rare in developed countries because many foods (especially flour and cereal) are fortified with niacin, meaning the vitamin is added during manufacturing. Pellagra still occurs in places where people face severe food shortages or have extremely limited diets.