A boil that swells on the upper lip can be caused by factors such as Staphylococcus aureus infection, septic infection, etc. Boils are usually due to infection by pathogenic bacteria, which leads to inflammatory lesions in the hair follicles and deep surrounding tissues of the follicles. The stimulation of inflammatory mediators may lead to a gradual increase in bacteria as well as bacterial metabolites, while the lip tissue is lax and thus prone to swelling. When a patient develops a boil, he or she may develop a high fever or even coma if not treated promptly. Boils can be treated with medications such as clindamycin and penicillin under the direction of a doctor. Hot compresses and infrared radiation can also be used in daily life to promote blood circulation and help the absorption of inflammation. When swelling occurs in patients with boils on the mouth, it may also be related to trauma and other factors, and should be avoided to squeeze freely.