OVERVIEW

What is Bell's palsy?

Many people have experienced this: going to bed with a perfectly normal face, only to wake up the next morning, look in the mirror, and be shocked—why is my mouth crooked? Speech is slurred, water leaks while brushing teeth, food debris gets stuck between teeth and cheeks when eating, blinking is impossible, and closing the eyes requires effort. It’s natural to feel worried and scared. In fact, this is likely Bell's palsy.

Bell's palsy, also known as Bell's facial paralysis, is a sudden-onset condition with an unclear cause that leads to unilateral facial muscle dysfunction. It may result from inflammation and swelling of the facial nerve due to viral infections or ischemia. The condition is named after 19th-century English anatomist Charles Bell, who first identified and described it.

Although Bell's palsy causes alarming symptoms, most patients recover fully. Prompt oral corticosteroid treatment within the first three days of onset can speed up recovery and reduce the risk of sequelae. However, a small number of patients may experience lingering complications like facial muscle spasms.

What is the facial nerve? What does it do?

The human body has 12 pairs of cranial nerves, and the facial nerve is the 7th pair. Many assume it only controls facial muscle movement, but this is not the case.

The facial nerve is a mixed nerve with several key functions:

• Controls facial muscle movement for expressions.
• Stimulates the lacrimal, submandibular, and sublingual glands to secrete tears and saliva.
• Transmits taste sensations from the front two-thirds of the tongue to the brain.
• Relays sensory input from the external ear canal and auricle to the brain.

Thus, damage to the facial nerve (e.g., from trauma or surgery) can cause not only facial paralysis but also symptoms like reduced taste sensitivity, hyperacusis (sound sensitivity), and abnormal tear or saliva production. Symptoms vary depending on the location of the nerve damage.

Are Bell's palsy and idiopathic facial paralysis the same?

The English term for "idiopathic facial paralysis" is IFP, also called idiopathic facial palsy.

Most neurology textbooks in China equate Bell's palsy with idiopathic facial paralysis, but there are subtle differences.

"Idiopathic" refers to conditions with no identifiable cause, whereas some Bell's palsy cases are linked to specific viral infections. Therefore, Bell's palsy is not entirely synonymous with idiopathic facial paralysis. More accurately, Bell's palsy encompasses both idiopathic facial paralysis and other cases suspected to be caused by viruses.

Additionally, Chinese neurology textbooks often equate Bell's palsy with "facial neuritis." As a result, doctors in China commonly use the terms "Bell's palsy," "idiopathic facial paralysis," and "facial neuritis" interchangeably.

SYMPTOMS

What are the extracranial branches of the facial nerve?

The facial nerve divides into five terminal branches outside the skull, controlling the facial expression muscles from top to bottom. From top to bottom, they are: the temporal branch, zygomatic branch, buccal branch, mandibular branch, and cervical branch.

• Temporal branch: Controls the frontalis, orbicularis oculi, corrugator supercilii, and procerus muscles. Enables actions like frowning, tightly closing the eyes, scowling, and wrinkling the nose.
• Zygomatic branch: Controls the zygomaticus major, zygomaticus minor, levator anguli oris, levator labii superioris alaeque nasi, levator labii superioris, depressor septi nasi, nasalis, and dilator naris muscles. Enables actions like smiling, flaring the nostrils, raising the nose, and dilating/constricting the nostrils.
• Buccal branch: Controls the buccinator and upper orbicularis oris muscles. Enables actions like whistling, sucking, puckering, puffing the cheeks, and closing the mouth.
• Mandibular branch: Controls the risorius, depressor labii inferioris, depressor anguli oris, mentalis, and lower orbicularis oris muscles. Enables actions like smiling, pulling the lower lip downward, forming a dimpled chin, and closing the mouth.
• Cervical branch: Controls the platysma muscle. Enables pulling the corners of the mouth downward and, in coordination with other muscles, producing expressions of fear or disgust.

What symptoms and manifestations does Bell's palsy cause?

Bell's palsy typically causes unilateral facial paralysis.

• Definite symptoms include:

  • Shallow forehead wrinkles (frontalis) and nasolabial folds on the affected side (forehead wrinkles are also called "worry lines"; nasolabial folds are the grooves from the nose wings to the mouth corners).
  • Weak or absent forehead wrinkles on the affected side when raising the eyebrows.
  • Incomplete or weak eye closure on the affected side compared to the normal side, sometimes exposing the sclera (known as "Bell's phenomenon").
  • Facial asymmetry when smiling, with the mouth corner deviating toward the unaffected side.
  • Air leakage from the affected side when puffing the cheeks.

A simple way to determine the affected side: The side with shallow forehead wrinkles, shallow nasolabial folds, and incomplete eye closure is the side with facial nerve damage, while the side the mouth deviates toward when smiling is the unaffected side.

• Possible symptoms include: Ear or postauricular pain, reduced tear production, excessive tearing, eye pain, blurred vision, hyperacusis, reduced taste sensation, and decreased saliva production.

Why does Bell's palsy cause ear pain?

Some patients experience persistent dull pain behind the ear or pain upon pressure. Why does this happen?

This occurs because the facial nerve damage may involve the geniculate ganglion, which contains sensory cells receiving input from the eardrum, inner ear, outer ear, and external ear canal skin. When these nerve fibers are affected, postauricular pain can result.

CAUSES

What are the causes of Bell's palsy?

• It may be related to viral activation. The most common virus is herpes simplex virus (HSV), followed by varicella-zoster virus. Other viruses include cytomegalovirus, Epstein-Barr virus, adenovirus, rubella virus, mumps virus, influenza B virus, and coxsackievirus. Viruses may trigger an immune response, leading to facial nerve inflammation, demyelination, and paralysis.
• It may also be associated with facial nerve ischemia. For example, diabetes can cause microangiopathy, leading to facial nerve ischemia, inflammation, and swelling.
• Bell's palsy occurring in pregnant women during late pregnancy or postpartum may be related to fluid retention during pregnancy causing facial nerve compression or edema. It may also be associated with a hypercoagulable state during pregnancy, leading to thrombosis in the facial nerve's nutrient vessels and resulting in ischemic edema of the facial nerve.

Where is the site of facial nerve damage in Bell's palsy?

The site of facial nerve damage is in the facial nerve canal.

Normally, the facial nerve occupies only 25%–50% of the canal's diameter, leaving ample space. In Bell's palsy, the facial nerve swells due to inflammation, ischemia, or other reasons, causing a sudden increase in pressure within the canal. This compresses the nerve and restricts blood supply, leading to dysfunction.

Symptoms vary among Bell's palsy patients because:

• The location of nerve damage within the facial nerve canal differs, affecting symptoms like tear secretion, saliva secretion, hearing abnormalities, and taste abnormalities.
• The severity of nerve damage varies, resulting in differing degrees of facial paralysis.

Who is more prone to Bell's palsy?

• Generally, Bell's palsy is more common in adults, diabetics, immunocompromised individuals, and pregnant women (especially in late pregnancy).
• It is rare in children under 10 years old.
• The incidence is equal between males and females.

Since the exact cause remains unclear, it is currently believed to be associated with neurotropic viral infections. Some patients may develop Bell's palsy after exposure to cold environments, cold wind stimulation, or recent upper respiratory infections. However, this does not mean that cold exposure alone causes facial paralysis. Healthy individuals without viral infections need not worry excessively.

Why are diabetics more prone to Bell's palsy?

Diabetics have a 29% higher risk of Bell's palsy than non-diabetics because hyperglycemia damages the microvessels supplying nerves, leading to facial nerve ischemic swelling. Nighttime ischemia worsens, so Bell's palsy often occurs at night, with many patients waking up to discover facial paralysis.

Additionally, diabetics experience slower recovery and higher recurrence rates.

Screening blood sugar in Bell's palsy patients visiting the hospital may reveal previously undiagnosed diabetes. Early detection and active blood sugar control are crucial.

DIAGNOSIS

What are the warning signs of Bell's palsy? What symptoms should make you suspect you have this condition?

Most patients seek medical attention due to noticing a crooked mouth.

If the mouth is not crooked, small tests can help determine if there are signs of facial paralysis, such as closing the eyes, puffing the cheeks, or whistling in front of a mirror. If these actions cannot be performed or show obvious asymmetry between the two sides, facial paralysis is likely present.

If these abnormal symptoms appear suddenly, with or without accompanying symptoms like reduced taste, abnormal sensitivity to sound, or pain behind the ear, Bell's palsy should be considered, and medical attention should be sought promptly.

What tests will doctors perform for patients suspected of having Bell's palsy?

Bell's palsy is a common condition, and experienced doctors can diagnose it by taking a medical history, observing the patient's symptoms, and conducting a neurological examination.

However, sometimes, to rule out facial paralysis caused by brain issues, doctors may recommend a head CT or MRI scan to avoid missing a serious diagnosis.

Additionally, neurophysiological tests can assess the severity of facial nerve damage, helping doctors determine the prognosis.

What is the significance of neurophysiological tests for Bell's palsy?

Neurophysiological tests include electroneurography (ENoG) and electromyography (EMG).

• ENoG principle: Electrical stimulation is applied to the facial nerve trunk in front of the ear, and skin electrodes record the depolarization potential of facial muscles. The affected side's amplitude is compared to the healthy side. If the affected side's amplitude is above 10% of the healthy side, the likelihood of complete or near-complete recovery is high. If it is below 10%, full recovery is less likely but still possible.

• EMG principle: Needle electrodes record depolarization potentials of facial muscles at rest and during voluntary contraction. For patients with no response to facial nerve stimulation or very weak muscle contraction, EMG supplements ENoG by detecting residual nerve axons.

Do all Bell's palsy patients need neurophysiological tests?

No.

• Patients with mild facial paralysis usually recover well and do not require ENoG or EMG.
• Patients with severe facial paralysis benefit from ENoG or EMG to objectively assess nerve damage severity, predict recovery chances, and determine if facial nerve decompression is necessary.

Within 7 days of onset, Wallerian degeneration is still progressing, while after 14–21 days, neurophysiological test reliability declines. Therefore, these tests are typically performed 7–14 days after symptom onset.

How is the severity of facial paralysis classified?

Severity correlates with prognosis: mild cases recover faster and better, while severe cases recover more slowly.

The House-Brackmann scale grades facial paralysis severity from mild to severe (I–VI).

Grade I – Normal

• Normal facial muscle function in all areas.

Grade II – Mild dysfunction

• General: Slight weakness on close inspection, minimal synkinesis.
• At rest: Normal symmetry and tone.
• Motion: Normal forehead movement, complete eye closure with effort, slight asymmetry when smiling.

Grade III – Moderate dysfunction

• General: Obvious weakness but no disfigurement; possible synkinesis, contractures, or spasms.
• At rest: Normal symmetry and tone.
• Motion: Weak forehead movement, complete eye closure with effort, slight asymmetry when smiling forcefully.

Grade IV – Moderately severe dysfunction

• General: Obvious weakness and/or facial asymmetry.
• At rest: Normal symmetry and tone.
• Motion: No forehead movement, incomplete eye closure, asymmetric mouth movement.

Grade V – Severe dysfunction

• General: Barely perceptible motion.
• At rest: Asymmetry.
• Motion: No forehead movement, incomplete eye closure, minimal mouth movement.

Grade VI – Total paralysis

• No movement.

Besides Bell's palsy, what conditions can cause unilateral facial paralysis?

• Infections: Varicella-zoster virus, Lyme disease, syphilis, HIV, mycoplasma, otitis media, or otitis externa.

• Microvascular diseases: Diabetes, hypertension.

• Trauma: Temporal bone fracture damaging the facial nerve.

• Tumors: Facial nerve tumors (e.g., schwannoma) or adjacent tumors. Slowly progressing facial paralysis often suggests a tumor, though 20–27% of tumor cases present acutely.

• Iatrogenic injury: Cosmetic surgery, parotid gland surgery, acoustic neuroma resection, or other tumor removals near the facial nerve. Sometimes, sacrificing nerve function is unavoidable for complete tumor removal.

How does Bell's palsy differ from varicella-zoster virus-induced facial paralysis?

Varicella-zoster virus infection causing facial paralysis is called Ramsay Hunt syndrome (RHS). Unlike Bell's palsy, RHS includes skin blisters, vertigo, hearing loss, and severe ear pain. Doctors examine for ear blisters and ask about vertigo, vomiting, deafness, and ear pain to differentiate.

Compared to Bell's palsy, RHS recovery is slower, ear pain is more severe, and hearing loss risk is higher. Treatment requires corticosteroids plus antivirals.

Some zoster-infected patients without blisters may be misdiagnosed with Bell's palsy.

Can Bell's palsy cause bilateral facial paralysis simultaneously?

Bilateral facial paralysis is rare and usually not Bell's palsy. Possible causes include Guillain-Barré syndrome, sarcoidosis, Lyme disease, meningitis (infectious or cancerous), or bilateral neurofibromas (neurofibromatosis type II).

TREATMENT

Which department should Bell's palsy patients visit?

Neurology or Neurosurgery.

What are the treatment methods for Bell's palsy?

• Corticosteroids: The primary treatment for Bell's palsy. Early use can shorten the course of the disease and reduce the risk of sequelae. Oral corticosteroids should be started within 72 hours of onset.

• Antiviral drugs: For patients with severe facial paralysis (House-Brackmann grade ≥ IV), oral antiviral drugs may be added alongside corticosteroids.

• Eye care: Some patients experience incomplete eyelid closure and/or insufficient tear production, leading to excessive corneal dryness, reduced foreign body clearance, and in severe cases, corneal ulcers or blindness. Eye care is essential to maintain corneal moisture.

• Surgery: Since Bell's palsy involves facial nerve inflammation and compression, facial nerve decompression may theoretically relieve symptoms. However, not all patients are suitable for surgery.

How should Bell's palsy patients use corticosteroids for treatment?

Prednisone is typically prescribed at 60–80 mg/day for 7 days, followed by gradual tapering. Treatment should begin within 3 days of onset. The benefit of corticosteroids after 3 days remains unclear.

Are there side effects of oral corticosteroids for Bell's palsy?

Short-term use usually causes no severe side effects, though some may experience insomnia or excitement, which resolve after discontinuation. Long-term use can lead to hyperglycemia, central obesity, infections, osteoporosis, gastric ulcers, or hypokalemia. Patients should not avoid corticosteroids due to side effect concerns, as this may delay recovery.

How are antiviral drugs used for Bell's palsy?

Antivirals alone are ineffective. For severe cases (House-Brackmann ≥ IV), antivirals like acyclovir (0.2–0.4 g, 3–5 times/day) or valacyclovir (0.5–1.0 g, 2–3 times/day) may be added to corticosteroids for 7–10 days.

How should Bell's palsy patients care for their eyes?

For incomplete eyelid closure, use:

• Artificial tears (frequent application needed).
• Eye ointment (may blur vision; use at bedtime).
• Moisture chambers (specialized goggles).
• Eye patches (avoid direct corneal contact).

When is surgery needed for Bell's palsy?

Most patients recover well with medication (94% recovery rate with corticosteroids). Surgery (e.g., facial nerve decompression) is considered only for severe cases with >90% nerve degeneration on ENoG and no motor unit potentials on EMG. Risks include hearing loss, nerve damage, or CSF leakage.

Are acupuncture or physical therapy effective for Bell's palsy?

These methods are commonly used but lack reliable evidence. Current guidelines do not recommend them.

Can Bell's palsy patients fully recover?

Most recover within 2–4 weeks, with full recovery in 3–4 months. Even untreated, 70% recover by 6 months. Some may experience residual weakness, synkinesis, spasms, or crocodile tears.

What sequelae can Bell's palsy cause?

About 9% of patients develop:

• Facial spasms: Involuntary muscle twitching.
• Muscle contractures: E.g., narrowed eye fissure, deep nasolabial fold.
• Synkinesis: Misdirected nerve regrowth causing abnormal movements (e.g., mouth twitching when blinking or crocodile tears while eating).

What factors hinder Bell's palsy recovery?

Poor recovery is more likely with:

• Age >60 (60% incomplete recovery vs. 10–15% in those <30).
• Severe initial paralysis (House-Brackmann scale).
• Impaired taste or reduced saliva at onset.

What if facial paralysis persists beyond 3 months?

Evaluate for other causes (e.g., tumors, infections) via CT/MRI or lumbar puncture. Surgical options (e.g., eyelid implants, temporalis muscle transfer) or psychological support may be considered.

Can Bell's palsy recur?

Recurrence occurs in 4–14%, ipsilateral or contralateral. Recurrent cases warrant MRI/CT to rule out tumors or infections.

DIET & LIFESTYLE

Can Bell's palsy patients perform rehabilitation exercises on their own?

Yes, they can do the following exercises:

• Passive massage exercises for facial muscles: Massage the paralyzed facial muscles for 5–10 minutes each time, 2–3 times a day, with gentle and moderate pressure.

• Active functional exercises for facial muscles: Perform movements such as raising eyebrows, closing eyes, wrinkling the nose, showing teeth, puckering lips, and puffing cheeks in front of a mirror, 2–3 times a day, with 10–20 repetitions per movement.

What should Bell's palsy patients pay attention to in their diet?

There are no specific restrictions; a healthy and balanced diet is sufficient.

• When cooking, use less salt, less oil, and fewer high-salt seasonings. Avoid pickled vegetables, cured meats, etc.

• Do not rely solely on refined rice and white flour for staple foods. Replace some with whole grains, legumes, potatoes, pumpkin, etc.

• Balance meat and vegetables. Prioritize white meats like chicken, duck, and fish, and reduce fatty meats. Eggs and milk are important sources of protein and other nutrients.

• Vegetarians can eat more beans and bean products to supplement protein.

• Eat plenty of fresh fruits and vegetables.

• Avoid alcohol.

What should Bell's palsy patients pay attention to in daily life during treatment?

• During the acute phase, rest appropriately and keep the face warm. Wear a mask when going out, avoid washing the face with cold water, and stay away from direct cold drafts.

• Since the onset is often sudden, patients may feel nervous, anxious, fearful, or irritable. Some may worry about facial changes or fear poor treatment outcomes leading to sequelae. It is important to understand the disease correctly and maintain a positive attitude.

PREVENTION

Can Bell's Palsy Be Prevented?

The exact cause of this disease is unclear and may be related to viral infections or inflammatory reactions. Therefore, there is no highly effective preventive method. The best approach is to maintain a healthy diet, exercise regularly, and reduce the risk of viral infections.