Red pimples on the chest are usually associated with acne, folliculitis and atopic dermatitis. 1. Acne: The cause of acne is related to the increase of androgen level and the proliferation of Propionibacterium acnes, and the patient’s skin will appear pimples, papules and pustules, etc., which are mostly seen on the face and chest. 2. Folliculitis: the main manifestation of red papules or pustules, commonly found on the head, face, chest and back, etc., the cause of its pathogenesis and pathogen infection, excessive sweating, trauma and other factors. 3. Atopic dermatitis: clinical symptoms of dry skin, papules and itching, can be seen in the chest, lesions are red. The cause of the disease may be related to immune abnormalities, environmental and genetic factors. There are many reasons that lead to red acne on the chest, and it is recommended that the patient consult a doctor for examination and symptomatic treatment after clarifying the cause of the disease.