Melkersson-Rosenthal syndrome (MRS) is a disease that generally begins late in childhood and is characterized by swelling of facial features, most frequently the lips. The areas of swelling may include the eyelids. MRS is most likely to become evident in childhood or adolescence. The swelling and facial palsy are believed to be due to lymphatic stasis and the resulting buildup of protein. The swelling may be accompanied by inflammation. The swelling and paralysis may be unilateral or bilateral. Facial swelling may involve both lips, only one lip, or only one side of the lip. MRS flare-ups may be triggered by bacterial infections.