Possible causes of lip swelling include mouth and lip trauma, allergic reactions to food or substances, angioedema, and infection, according to MedicineNet. Additionally, conditions that affect the entire body can cause lip swelling.
Angioedema is swelling of the tissue underneath the skin, states MedicineNet. The swollen tissue is commonly concentrated around the eyes and lips. Herpes can cause blisters and localized lip swelling, while other inflammatory skin conditions can cause lip inflammation and swelling. Medical conditions that affect the whole body, sometimes associated with fluid retention or swelling, can cause lip swelling, although the occurrence is less common than with other causes.