Swelling of the lips can arise due to different conditions. Trauma or injury to the lip and mouth area is an obvious cause of swollen lips. Allergic reactions, either to foods, medications, or other substances, can often be accompanied by swelling of the lips. This may be accompanied by other allergic symptoms, such as hives and itching.
Angioedema is a condition in which there is swelling of the tissue beneath the skin, and this is often concentrated around the eyes and lips. Some infections (such as herpes simplex virus infection) can result in blisters (sometimes referred to as cold sores) and localized swelling of the lips
Infections and inflammatory conditions of the skin can also lead to inflammation and swollen lips (cheilitis). Less commonly, medical conditions or illnesses that affect the entire body may cause lip swelling, sometimes in association with fluid retention or swelling in other areas of the body.