There are many reasons for red rash on neck, such as allergic factors, infectious factors, blood system abnormalities, etc. 1. Allergic factors: contact with allergens in the neck can trigger an allergic reaction, manifesting a red rash on the neck, which can be diversified in form and accompanied by itching, flaking, oozing and other phenomena. 2. Infectious factors: If infants and young children have a red rash on the neck, accompanied by symptoms of upper respiratory tract infections, it is necessary to consider that it belongs to the infectious disease rash disease, such as infantile emergency rash, rubella and so on. 3. blood system abnormalities: red rash on the neck if belongs to the small petechiae, pressure does not fade, and not high out of the skin, accompanied by other parts of the body bleeding phenomenon, such as stool color black, often nosebleeds, etc., it may be and thrombocytopenia has a certain relationship. There are many reasons for the red rash on the neck, after the symptoms appear, it is recommended to go to the hospital for examination in time, so that the doctor can evaluate the condition according to the symptoms and examination, and give targeted treatment.