Mouth swelling is most commonly caused by angioedema, which can cause sudden swelling of the lips, which is also a kind of allergic disease. The onset of the disease is relatively sudden and occurs in the loose connective tissue areas of the head and face such as the lips, tongue, cheeks, eyelids, earlobes, and throat, etc. At first, the affected area feels itchy and burning pain, and then swelling occurs, which is very obvious and expands very rapidly. Patients can feel the swelling and elasticity of the affected area, and the pain is not obvious. If the swelling occurs on the lip, it may cause lip thickening and lifting; if it occurs on the tongue, it may cause difficulty in eating and speaking; if it occurs on the epiglottis, it may cause difficulty in breathing, and if tracheotomy is not performed in time, it may lead to death by asphyxia. The swelling also subsides relatively quickly, and can subside within a few hours or 1 to 2 days without leaving a trace. Inflammation can cause swelling of the lips to some extent. Most likely, cellulitis has occurred. Cellulitis is a very serious inflammation which refers to a diffuse purulent infection of extensive skin and subcutaneous loose connective tissue. If this inflammation occurs, it will not only cause swelling of the lips, but may also cause severe sepsis and even life-threatening. There is also apical inflammation of the front teeth that can also cause lip swelling, and the above cases should be seen immediately at the hospital. If there is a swollen mouth, you must first find out whether it is inflammation or allergy to avoid detours and delayed treatment.