Whether a rash is contagious or not is related to the type of disease; some rashes are contagious and can infect others, but some rashes are not contagious. Rashes that are contagious can be spread through respiratory transmission, blood transmission, and sexual transmission. Common types include scarlet fever and acne. For respiratory transmitted diseases such as scarlet fever, patients should be careful to avoid places where people gather and to wear a mask. Rashes that are not contagious, such as allergic urticaria, can be treated by applying topical medications. It is also important to avoid contact with allergens and try to maintain a light diet during the rash to avoid aggravation of the disease. Therefore, it is important to consult a doctor for a clear diagnosis of the rash when it occurs. When the rash is contagious, it should be protected and actively treated.