[1] They may include muscle twitching, weakness, or total loss of the ability to move one or, in rare cases, both sides of the face.

[4] Risk factors include diabetes, a recent upper respiratory tract infection, and pregnancy.

[1] Other conditions that can cause facial weakness include brain tumor, stroke, Ramsay Hunt syndrome type 2, myasthenia gravis, and Lyme disease.

[1] It is named after Scottish surgeon Charles Bell (1774–1842), who first described the connection of the facial nerve to the condition.

[1] Although defined as a mononeuritis (involving only one nerve), people diagnosed with Bell's palsy may have "myriad neurological symptoms", including "facial tingling, moderate or severe headache/neck pain, memory problems, balance problems, ipsilateral limb paresthesias, ipsilateral limb weakness, and a sense of clumsiness" that are "unexplained by facial nerve dysfunction".

[13][14] The facial nerve controls many functions, such as blinking and closing the eyes, smiling, frowning, lacrimation, salivation, flaring nostrils and raising eyebrows.

Because of this, people with Bell's palsy may present with loss of taste sensation in the anterior two thirds of the tongue on the affected side.

Reactivation of an existing (dormant) viral infection has been suggested as a cause of acute Bell's palsy.

[19] Other viruses and bacteria that have been linked to the development of Bell's palsy include HIV, sarcoidosis and Lyme disease.

[medical citation needed] This new activation could be triggered by trauma, environmental factors, and metabolic or emotional disorders.

[22] In December 2020, the U.S. FDA recommended that recipients of the Pfizer and Moderna COVID-19 vaccines should be monitored for symptoms of Bell's palsy after several cases were reported among clinical trial participants, though the data were not sufficient to determine a causal link.

Possible causes of facial paralysis include tumor, meningitis, stroke, diabetes mellitus, head trauma and inflammatory diseases of the cranial nerves (sarcoidosis, brucellosis, etc.).

In some research, the herpes simplex virus type 1 (HSV-1) has been identified in a majority of cases diagnosed as Bell's palsy through endoneurial fluid sampling.

One study found that 45% of patients are not referred to a specialist, which suggests that Bell's palsy is considered by physicians to be a straightforward diagnosis that is easy to manage.

[11] Other conditions that can cause similar symptoms include herpes zoster, Lyme disease, sarcoidosis, stroke, and brain tumors.

[29] The first sign of about 80% of Lyme infections, typically one or two weeks after a tick bite, is usually an expanding rash that may be accompanied by headaches, body aches, fatigue, or fever.

[28] One disease that may be difficult to exclude in the differential diagnosis is the involvement of the facial nerve in infections with the herpes zoster virus.

[36] One review found that antivirals (such as aciclovir) are ineffective in improving recovery from Bell's palsy beyond steroids alone in mild to moderate disease.

[8] They are commonly prescribed due to a theoretical link between Bell's palsy and the herpes simplex and varicella zoster virus.

[46] Most people with Bell's palsy start to regain normal facial function within three weeks—even those who do not receive treatment.

Around 9% of people have some sort of ongoing problems after Bell's palsy, typically the synkinesis already discussed, or spasm, contracture, tinnitus, or hearing loss during facial movement or crocodile-tear syndrome.

This is thought to be due to faulty regeneration of the facial nerve, a branch of which controls the lacrimal and salivary glands.

Bell's palsy is not a reportable disease, and there are no established registries for people with this diagnosis,[53] which complicates precise estimation.

[1] The Persian physician Muhammad ibn Zakariya al-Razi (865–925) detailed the first known description of peripheral and central facial palsy.

[54][55] Cornelis Stalpart van der Wiel (1620–1702) in 1683 gave an account of Bell's palsy and credited the Persian physician Ibn Sina (980–1037) for describing this condition before him.

Scottish neurophysiologist Sir Charles Bell read his paper to the Royal Society of London on July 12, 1821, describing the role of the facial nerve.

The ad had the adverse effect of increasing Chrétien's lead in the polls and the subsequent backlash clinched the election for the Liberals, which the party won in a landslide.

On April 25, 2024, Joel Hans Embiid of the Philadelphia 76ers scored 50 points in Game 3 of the 76ers' first-round playoff series versus the New York Knicks while suffering from a mild case of Bell's Palsy.