Bell palsy is the most common type of facial neuropathy, with an average yearly incidence (in the United States and internationally) of about 0.02%. Men and women are affected equally, although pregnant individuals have a slightly higher risk, as do individuals with diabetes. Bell palsy can occur in children, but the condition more commonly affects adolescents and adults. Bell palsy is a diagnosis of exclusion. Patients typically present with acute onset of unilateral facial paralysis, but it may sometimes be bilateral. It may or may not be associated with pain or facial numbness.

Although the etiology for Bell palsy is idiopathic, autoimmune and/or viral-induced inflammation of the peripheral nerve is believed to play a role. Herpes zoster sometimes causes Bell palsy and is associated with vesicles by the ear (Ramsay-Hunt syndrome). Herpes simplex, cytomegalovirus, Epstein-Barr virus, and Borrelia infections including Lyme disease have also been associated. The use of some medications has rarely been associated with Bell palsy.

Severe hypertension has been associated with facial palsy, particularly in children but also in adults. In children, there may be a substantial delay to diagnosis of hypertension; one study notes a median time of 45 days between the first symptoms of peripheral facial palsy and a diagnosis of arterial hypertension. Another study reports that adults with uncontrolled hypertension due to poor medication compliance have a higher incidence of Bell palsy.

Patients may complain of difficulty with their speech and eating because of mouth droop. Due to the paralytic eyelid muscles, patients may have incomplete eye closure, causing their eyes to feel dry and leading to excessive corneal exposure and sometimes ulceration. Patients may have difficulty blinking, altered taste and tear production, and hyperacusis. The palsy is usually sudden in onset, with maximal facial weakness developing within 2 days. Facial or retroauricular pain may also be associated, but severe pain is highly suggestive of herpes zoster infection.

Eighty-four percent of patients with Bell palsy have spontaneous recovery within 2-3 months. Although most patients recover, up to 30% have residual pain and facial asymmetry. Aberrant regeneration (synkinesis) may occur after an acute episode.