Pimples on the side of the mouth may be acne, herpes simplex, eczema, etc. 1. acne: acne is a relatively common dermatological disease, more common among teenagers, usually associated with abnormal hormone levels, sebaceous gland secretion, follicular epithelial hyperkeratosis, Propionibacterium acnes infection, etc., the main manifestation is that the local skin will appear pimples, inflammatory papules, nodules and other lesions. 2. Herpes simplex: acne around the mouth may also be caused by herpes simplex virus infection caused by herpes simplex, the main manifestation is that there will be clusters of local blisters or scabs, there may also be slight pain and itching symptoms, usually infectious. 3. Eczema: it occurs in infants and children, mostly related to food, lip licking, etc., which leads to eczema on the side of the mouth, mainly manifested as erythema, papules, pimples, etc., accompanied by itching. If you have acne on the side of the mouth, it is recommended to actively go to a regular hospital, by the doctor for standardized treatment, do not blindly deal with it, so as not to cause adverse consequences.