In clinical dermatology there are many diseases that can cause a red rash on the body and are not painful, there are many reasons that can cause this clinical manifestation, the main common in daily life, can cause a red rash on the body and not painful, the following diseases: 1, prickly heat. In hot weather, many patients will appear prickly heat, that is, the skin of the whole body appears red pinpoint-sized corn papules, not necessarily accompanied by pain and itching. 2, senile hemangioma. The patient with senile hemangioma will appear green bean to soybean size, red painless papules. 3, insect bite dermatitis. Most of them are a kind of hypersensitivity reaction due to mosquito bites and will appear red bumps of rice grain size. 4, pityriasis rosea, most patients itching is not obvious.