A red corn-like papule of the skin with intense itching and tingling sensation, commonly seen in hot and humid climates, caused by obstruction of sweat ducts or impaired excretion. So what is the differential diagnosis? 1, roseola-like rash: common in brucellosis 10% of cases occur non-specific rash, more common for measles-like, scarlet fever-like and roseola-like rash. Epidemiological data and occupation are of great value in assisting the diagnosis of the disease. If some specific clinical manifestations of the disease are also present, such as undulant fever and orchitis, the diagnosis can be basically established. Positive results of cultures of blood, bone marrow and pus are the basis for confirming the diagnosis. The agglutination test (or ELISA, complementary junction test, etc.) should be measured month by month and week by week, and those with high efficiency or exponential increase in potency have diagnostic value. In chronic patients, ELISA or anti-human globulin test should be performed when the agglutination test is negative, and 2-ME test should be performed to distinguish natural infection from artificial immunity, or to clarify whether the disease is active. 2, pellagra-like rash: common in Hartnup disease, is a hereditary amino acid metabolic disease, also known as hereditary niacin deficiency, clinical manifestations of pellagra-like rash, neurological damage and amino acid urine. 3, erythema-like rash: is a very common symptom of skin disease, many skin diseases have this symptom. It manifests as scattered red bumps on the skin and red patches. 4, acne-like rash: It is commonly found in people who have received long-term cosmetic treatment on the face, manifesting as limited acne, inflammatory papules, and desquamative erythematous rash.