Pimples generally refer to small pimples caused by acne or allergies. Pimples under the mouth may be caused by endocrine metabolism disorders, infectious factors, and allergic factors. 1. Endocrine metabolism disorders: staying up late for a long time and having an irregular diet can lead to endocrine metabolism disorders, hormone imbalance in the body, which can increase sebaceous gland secretion and lead to follicle pore clogging, which can lead to pimples on the lower side of the mouth. 2. Infection factors: due to more follicular holes under the mouth, not paying attention to daily hygiene may lead to bacterial infection in the follicular pore area, and after the aggravation of the infection, it will make the follicle area appear pimples, accompanied by redness, swelling, pain and itching, and there is pus inside. 3. Allergic factors: such as consuming some allergic food, allergic reactions, can also make the corners of the mouth pimples, usually red pimples, accompanied by intense itching. Acne under the mouth, and with some obvious abnormal manifestations, it is recommended to go to the hospital dermatology department in time for appropriate examination and treatment, to avoid adverse effects.