What should you know about half lip swollen?

A local bite, minor injury, dental problem, cold sore, contact reaction, or irritation from food or cosmetics can affect one side. Sudden swelling can also be angioedema, a deeper swelling of the skin that may occur with hives or without them. [Angioedema](/conditions/angioedema/) can affect the lips, eyelids, tongue, or throat. The timing of a new medicine, meal, dental treatment, or product is useful information, but does not establish the cause by itself.

Stop a suspected new cosmetic, lip product, or food and rinse the area gently. A cool compress wrapped in cloth may ease discomfort. Do not pierce, squeeze, or apply leftover prescription medicine. If a clinician has previously given you an allergy action plan, follow it. Photograph the swelling and note when it began, what touched the area, and whether it is spreading.

Call emergency services immediately for swelling of the tongue or throat, trouble breathing, wheezing, faintness, confusion, or difficulty swallowing. Seek same-day medical advice for rapidly increasing swelling, hives, fever, severe pain, pus, a dental infection concern, or swelling after a medicine. Mild stable swelling still deserves review if it does not settle or keeps returning.

Could this be angioedema, infection, trauma, or contact irritation? Which symptoms would require emergency treatment? Should I avoid a medicine or product? Do I need dental or allergy assessment? What should I record if it happens again?