There are many reasons why a bump under the lower lip hurts when pressed, such as sebaceous cysts, Propionibacterium acnes infection, and folliculitis. 1. Sebaceous cysts: Sebaceous gland ducts are blocked, resulting in the oil secreted by the sebaceous glands cannot be excreted normally, and due to the accumulation of oil, cysts are gradually formed, which will lead to the phenomenon of a bump under the lower lip that hurts when pressed. 2. Propionibacterium acnes infection: Propionibacterium acnes infection can induce localized acne, acne development to a certain extent, it will cause a bag under the lower lip pain when pressed, and you can also observe the contents. 3. Folliculitis: usually do not pay attention to the lower lip follicle hygiene clean, or skin breakage and other problems, may induce folliculitis, resulting in local redness, swelling, pain phenomenon. The reason why a bag grows under the lower lip and hurts when pressed is many, after the symptoms, it is recommended to go to the hospital in time to improve the examination, identify the causes and take standardized treatment, do not ignore the symptoms and take them lightly.