What Causes Bell’s Palsy? Triggers & Risk Factors

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What Causes Bell’s Palsy? Triggers & Risk Factors

By Butler Family Health Center · Published 2026-09-16 · Last updated 2026-09-16

What causes Bell’s palsy? Triggers and risk factors center on viral infections and immune system disruption that inflame the facial nerve, also called cranial nerve VII. The herpes simplex virus type 1 is the most commonly linked cause. When the virus reactivates, it swells the nerve inside a narrow bony canal in the skull, blocking signals to facial muscles. This leads to sudden weakness or paralysis on one side of the face. Risk factors include diabetes, pregnancy, recent illness, high stress, and a weakened immune system. Symptoms typically appear within 48 to 72 hours. Early treatment within the first three days offers the best chance of full recovery.

What Is Bell’s Palsy?

Bell’s palsy is sudden, temporary weakness or paralysis on one side of the face caused by inflammation of the facial nerve. The facial nerve controls the muscles that help you smile, blink, raise your eyebrows, and move your lips. When that nerve becomes inflamed or compressed, those muscles stop receiving clear signals.

Here’s the distinction that matters most: Bell’s palsy is not a stroke. A stroke involves a disruption in blood flow to the brain and can cause weakness on an entire side of the body. Bell’s palsy affects only the facial nerve and doesn’t involve the brain’s blood supply. We mention this because the fear of stroke is often the first thing people feel when a face droops unexpectedly, and it’s important to know the difference.

Symptoms usually appear within 24 to 72 hours. You may notice drooping on one side of the face, drooling, difficulty closing one eye, or changes in taste. Most people recover fully within three to six months with proper care started early.

How Is Bell’s Palsy Different From a Stroke?

The fastest way to tell the difference is to check the forehead. In Bell’s palsy, the forehead muscles on the affected side are also weak, so the person can’t raise that eyebrow. In a stroke, the forehead is often spared because the brain has two pathways controlling those muscles. If you also notice arm weakness, slurred speech, or vision changes, call emergency services right away. Those symptoms point to stroke, not Bell’s palsy. Don’t wait to see if it passes.

What Virus Most Often Causes Bell’s Palsy?

The herpes simplex virus type 1, commonly known as HSV-1, is the most common virus linked to Bell’s palsy. HSV-1 is the same virus responsible for cold sores. After a first infection, the virus doesn’t leave the body. Instead, HSV-1 lies dormant inside nerve tissue, sometimes for years.

When the immune system weakens due to stress, illness, or fatigue, HSV-1 can reactivate. The virus then travels along the facial nerve and causes swelling inside a narrow passage in the skull called the fallopian canal. That swelling compresses the nerve and cuts off the normal signals it sends to facial muscles.

What Is the Fallopian Canal and Why Does It Matter?

The fallopian canal is a bony tunnel inside the skull that the facial nerve passes through. The canal fits the nerve very snugly. When inflammation causes the nerve to swell even slightly, there’s almost no room for that swelling to expand. The compressed nerve loses its ability to carry signals efficiently, and facial muscle function drops rapidly. That tight-fit design is why Bell’s palsy symptoms can appear so suddenly and feel so severe even when the underlying cause is a relatively common virus. It’s a structural problem as much as a viral one.

Other viruses also linked to Bell’s palsy onset include:

  • Herpes zoster (the virus that causes shingles and chickenpox)
  • Epstein-Barr virus (linked to mononucleosis)
  • Cytomegalovirus (CMV)
  • Adenovirus (a common cause of respiratory infections)
  • HIV (in cases where immune suppression is significant)

What Triggers a Bell’s Palsy Episode?

A Bell’s palsy episode is often triggered by events that weaken the immune system and allow a dormant virus to reactivate. The immune system normally keeps the herpes simplex virus suppressed. When something disrupts that balance, the virus gets an opportunity to become active again.

Commonly reported triggers include:

  • Recent upper respiratory infection, cold, or flu
  • Significant physical or emotional stress
  • Sleep deprivation or prolonged exhaustion
  • Ear infection or inner ear inflammation
  • Immune suppression from illness or medication

We see patients who can point to a stressful stretch at work or a bad cold they had two weeks earlier. The trigger isn’t always obvious in the moment, but looking back, it’s often there.

Does Cold Weather Trigger Bell’s Palsy?

Some patients report that cold air exposure or a sudden drop in temperature happened just before their symptoms began. Research on this connection is ongoing and hasn’t confirmed cold weather as a direct cause. One working theory is that cold air may irritate the facial nerve directly as it passes near the ear. Another is that people get more respiratory infections in cold seasons, and those infections are the real trigger. In our experience, cold exposure looks like a contributing factor in some cases, not a cause on its own.

Who Is Most at Risk for Bell’s Palsy?

Anyone can develop Bell’s palsy, but certain groups face a higher risk than the general population. Bell’s palsy affects roughly 40,000 people in the United States each year, according to the National Institute of Neurological Disorders and Stroke.

Risk GroupReason for Elevated RiskPregnant women (third trimester or postpartum)Immune system changes and fluid retention increase nerve pressurePeople with diabetesNerve health is compromised and immune response is reducedAdults ages 15 to 45Most commonly diagnosed age range across clinical studiesIndividuals with a family history of Bell’s palsyPossible genetic predisposition to facial nerve sensitivityPeople with recent viral illnessActive or recently resolved infection stresses immune defensesThose with weakened immunityLower ability to keep dormant viruses suppressed

Pregnant women face a substantially higher risk than non-pregnant adults, particularly in the third trimester and in the weeks after delivery. People with diabetes face elevated risk because high blood sugar damages the small blood vessels that feed nerves over time. We’ve seen both groups come in after waiting a day or two to see if things improved on their own. Don’t do that. If you’re managing either of those conditions and you notice any facial weakness, call us or get to a provider the same day.

Is Bell’s Palsy More Common in Women or Men?

Bell’s palsy affects men and women at roughly equal rates across the general population. The exception is during pregnancy, where women see a higher incidence rate. Outside of pregnancy, neither sex appears to carry a meaningfully higher baseline risk. Age matters more than sex when predicting who’s likely to develop Bell’s palsy.

How Does Nerve Inflammation Cause Facial Paralysis?

When the facial nerve becomes inflamed, it swells inside a tight bony channel in the skull and loses the ability to send signals to face muscles. Swelling in the fallopian canal squeezes the nerve the same way a pinched nerve in the back squeezes a spinal nerve root: pressure builds, signal quality drops, and muscle function fails.

Reduced blood flow makes the problem worse. Compression slows circulation inside the nerve, which accelerates signal failure. That’s why symptoms appear so quickly after the inflammation starts.

What Happens to the Facial Nerve During Bell’s Palsy?

The inflammation process follows a recognizable pattern. First, a trigger (usually viral reactivation) sets off an immune response inside the nerve. The nerve tissue swells in reaction to the virus or immune activity. That swelling presses against the walls of the fallopian canal, which can’t expand. Blood flow to the nerve decreases as compression increases, and nerve signals to facial muscles weaken or stop entirely. Nearby structures also become affected, which can disrupt taste on the front two-thirds of the tongue, reduce tear production in the eye, and cause heightened sensitivity to sound in one ear.

Recovery happens as the inflammation resolves and the nerve regains its ability to carry signals. In mild cases, the nerve recovers quickly. In severe cases, the nerve may need several months to regenerate enough function for full muscle control. That range is wide, and it’s one reason early treatment matters so much.

What Conditions Raise Your Risk of Bell’s Palsy?

Several underlying health conditions make the facial nerve more vulnerable to inflammation and compression. Knowing which conditions carry higher risk helps you recognize symptoms faster and seek care sooner.

  • Diabetes: High blood sugar damages the small blood vessels that supply the facial nerve. This reduces the nerve’s ability to withstand inflammation and slows recovery after an episode.
  • High blood pressure: Hypertension strains the vascular supply that keeps nerve tissue healthy and has been linked to elevated Bell’s palsy risk in some research.
  • Autoimmune conditions: Conditions that alter normal immune function may make the facial nerve more susceptible to inflammation in some individuals.
  • Upper respiratory infections: Any recent respiratory illness, including influenza, places the immune system under stress and can allow dormant viruses to reactivate.
  • COVID-19: Bell’s palsy has been reported in association with COVID-19 infection. Researchers believe the connection may involve systemic inflammation or immune system disruption triggered by the virus. Anyone who develops sudden facial weakness during or after a COVID-19 illness should seek evaluation right away.

Is Bell’s Palsy Linked to COVID-19?

Yes, Bell’s palsy has been reported in association with both COVID-19 infection and, in some cases, with immune responses following COVID-19 illness. Researchers believe the connection may involve systemic inflammation or immune system disruption triggered by the virus. The overall risk tied to COVID-19 appears similar in scale to the risk linked to other viral infections. Anyone who develops sudden facial weakness during or after a COVID-19 illness should seek evaluation right away.

When Should You See a Provider for Bell’s Palsy?

See a provider immediately if one side of your face suddenly droops, because early treatment within 72 hours gives the best recovery results. The three-day window matters because corticosteroids, the primary medical treatment for Bell’s palsy, are most effective when started before significant nerve damage has set in.

A doctor can rule out stroke first. Stroke and Bell’s palsy share some visible symptoms, and confirming the correct diagnosis is the first step in getting the right care. Once a stroke is ruled out, a provider can begin a corticosteroid course to reduce nerve swelling and support faster healing.

Physical therapy can help you maintain muscle tone and prevent stiffness while the nerve recovers. At Butler Family Health Center, we work with patients on nervous system and whole-body support during recovery, and we’re glad to talk through what that looks like for your specific situation. Give us a call and we’ll tell you straight whether what we do fits where you are in recovery and if we’d advise treating your bell’s palsy through chiropractic treatments.

Don’t wait. Delayed treatment raises the chance of incomplete muscle recovery or prolonged weakness. The earlier you act, the better the nerve’s ability to heal fully.

For a detailed overview of what the facial nerve is and how inflammation affects it, the facial nerve inflammation overview from NINDS at the National Institute of Neurological Disorders and Stroke is a reliable reference.

The Bottom Line

Bell’s palsy is most often caused by viral reactivation, particularly HSV-1, which inflames and compresses the facial nerve inside the fallopian canal. Risk factors include diabetes, pregnancy, weakened immunity, recent illness, and high stress. Knowing these factors helps you recognize symptoms faster and act within the 72-hour window that offers the best chance of full recovery. If you want to talk through supportive care during recovery, call Butler Family Health Center in Centennial, CO. We’re happy to tell you exactly what we can and can’t help with so you can make a good decision for yourself.