Research links Bell's palsy to several viral conditions, such as mononucleosis, chicken pox or shingles, and cold sores or genital herpes, although the exact reason it occurs remains unknown, according to Mayo Clinic. The viral conditions cause inflammation and swelling of the facial nerve as it passes through a narrow passageway in the bone. This nerve affects facial muscles, tears, taste, saliva and one of the small bones in the inner ear.
The risk of Bell's palsy increases in pregnancy, especially during the third trimester through the first week after giving birth, warns Mayo Clinic. Other risk factors include upper respiratory infections and diabetes. Some patients with facial palsy may have a genetic predisposition to the disease, especially if they experience recurrent episodes.
Although most mild cases of Bell's palsy get better in about a month, there is a risk of long-term complications. If the patient is unable to close the eye, the excessive dryness may cause scratching of the cornea, affecting the vision or causing blindness. Some patients suffer permanent damage to the facial nerve, reports Mayo Clinic. In others, the redirected nerve growth causes involuntary contraction of one muscle group when trying to move another.
Doctors may prescribe corticosteroids for patients with Bell's palsy. Physical therapy helps to prevent atrophy of the temporarily paralyzed muscles, advises Mayo Clinic. Over-the-counter medications, eye drops and warm compresses also help to relieve the symptoms.