Red pimples on the chest may be caused by folliculitis, acne, urticaria, contact dermatitis and other causes. 1. Folliculitis: when the hair follicles on the chest are damaged, they are easily infected by pathogenic microorganisms, which leads to folliculitis, which manifests itself as red papules or pustules on the skin surface, and sometimes the pustules rupture and crust, which may be accompanied by itching and pain. 2. Acne: the cause of the disease is still unclear, mainly occurs in the face, chest, back and shoulder blades, mainly manifested as pimples, pimples, pustules, nodules, etc., often accompanied by sebum overflow. 3. Urticaria: Urticaria may be related to food and drug allergies, infections, mental and endocrine factors, etc. It can appear in any part of the human body, mainly manifested as wind or angioedema, mostly accompanied by itching symptoms. 4. Contact dermatitis: when the chest comes into contact with certain external substances, such as animal fur, shower gel, soap, etc., may trigger contact dermatitis, manifested as skin erythema, edema, or the size of a needle tip dense pimples and other symptoms. Red pimples on the chest may also have other causes, it is recommended to go to the hospital in a timely manner to improve the examination, clear cause to give targeted treatment.