Pellagra refers clinically to niacin deficiency, and its symptoms include dermatitis and diarrhea. The causes of niacin deficiency are mostly related to the deficiency of niacin vitamins, including insufficient niacin intake, excessive niacin demand, and abnormal niacin metabolism. Typical symptoms of niacin deficiency are dermatitis, with sun spots, erythema, edema, and itching and pain on exposed areas, such as the back of the hands, neck, and lower legs. In addition, the patient’s skin lesions will gradually turn darker in color over time, and there will be skin thickening, hyperpigmentation, roughness, and dry scales. Some patients may also have symptoms of diarrhea and dementia. If the above symptoms occur, it is considered to be caused by niacin deficiency, and patients are advised to go to regular hospitals to clarify the cause.