There are two possible reasons for the sudden thickening of the lower lip and the outer side of the lip. 1. the swelling of the local soft tissues caused by accidental contusion, which will naturally disappear after a few days of rest. 2. it may be caused by allergies, such as eating allergy-prone foods or drinks that stimulate the lower lip and induce allergic inflammation, resulting in swollen lips. In this case, some patients may also experience itching of the lower lip. The treatment can usually be oral anti-allergy medication, commonly used is loratadine, cetirizine and other drugs. If the sudden swelling is very strong, and also accompanied by the whole body of the wind-like hives, this situation must go to the hospital to deal with, generally can be intramuscular injection benadryl or intravenous push dexamethasone anti-allergic, anti-inflammatory treatment.