Facial paralysis happens when the facial nerve, the seventh cranial nerve, is damaged, compressed, or inflamed somewhere along its path from the brainstem to the muscles of the face. The most common cause by far is Bell’s palsy, an idiopathic condition linked to viral reactivation that accounts for the majority of cases. But infections, trauma, tumors, autoimmune disorders, and stroke can all produce facial paralysis through different mechanisms.
How the Facial Nerve Works
The facial nerve takes a remarkably long and winding route through the skull before it reaches your face. It exits the brainstem near the base of the brain, enters a narrow bony tunnel called the facial canal inside the temporal bone (the bone around your ear), and eventually emerges through a small opening behind the earlobe called the stylomastoid foramen. From there, it fans out to control the muscles responsible for facial expression: raising your eyebrows, closing your eyes, smiling, and puckering your lips.
That narrow bony canal is the problem. When the nerve swells from inflammation or infection, it has almost no room to expand. The resulting compression chokes off the nerve’s ability to send signals, and your facial muscles on that side stop responding. Mild swelling causes reversible signal blockage. Prolonged or severe compression leads to a deeper form of nerve damage where the nerve fibers themselves begin to break down, a process called Wallerian degeneration, which takes much longer to heal.
Bell’s Palsy: The Most Common Cause
Bell’s palsy is the diagnosis when no other identifiable cause can be found, but strong evidence points to viral reactivation as the trigger. Herpes simplex virus type 1 (the cold sore virus) has been detected in up to 50% of Bell’s palsy cases, and the varicella-zoster virus (the chickenpox/shingles virus) in roughly 13%. These viruses lie dormant in nerve tissue after initial infection and can reactivate years or decades later, causing inflammation that swells the nerve inside its bony canal.
The good news is that Bell’s palsy has a favorable outlook. About 80% of people recover completely without any treatment. With prompt steroid therapy started within 48 hours of symptom onset, recovery rates climb to 90% to 97%. The steroids work by reducing the swelling that’s compressing the nerve, giving it room to recover before permanent damage sets in.
Bell’s palsy typically affects one side of the face and comes on suddenly, often overnight. You might wake up unable to close one eye, with one side of your mouth drooping. Taste can be altered on one side of the tongue, and sounds may seem unusually loud in one ear.
Ramsay Hunt Syndrome
When the varicella-zoster virus reactivates specifically in the facial nerve near the ear, the result is Ramsay Hunt syndrome. This is essentially shingles of the facial nerve, and it’s more aggressive than Bell’s palsy. The hallmark is a painful rash with fluid-filled blisters on, in, or around one ear, combined with facial paralysis on that same side.
Beyond the paralysis and rash, Ramsay Hunt syndrome often causes ear pain, hearing loss, ringing in the ear, vertigo, and abnormal eye movements. Some people notice altered taste on one side of the tongue or difficulty producing tears normally. Recovery tends to be slower and less complete than with Bell’s palsy, particularly if treatment is delayed.
Lyme Disease
The bacterium spread by tick bites can attack the facial nerve as part of a broader neurological infection. CDC data shows that about 9 out of every 100 reported Lyme disease cases involve facial palsy. Unlike most other causes, Lyme disease can produce facial paralysis on both sides of the face simultaneously, which is an important diagnostic clue. If you develop facial weakness during tick season or after spending time in wooded areas, Lyme testing is a standard part of the workup.
Trauma and Skull Fractures
A blow to the head that fractures the temporal bone can injure the facial nerve directly. The timing of the paralysis tells doctors a lot about the severity. Complete paralysis that appears immediately after the injury suggests the nerve has been severed, which is fortunately uncommon. Paralysis that develops gradually over hours, days, or even weeks is more likely caused by swelling around the nerve and usually responds to conservative treatment.
In crush-type injuries, the nerve damage unfolds slowly. Some patients don’t reach full paralysis until several weeks after the fracture because the nerve fibers break down gradually. When the timing of onset is unclear, doctors treat it as if the paralysis started immediately to avoid missing a more serious injury.
Tumors
Growths in or near the parotid gland (the large salivary gland in front of each ear) can compress or invade the facial nerve. The key difference from Bell’s palsy is the timeline. Tumor-related facial paralysis typically develops gradually over weeks to months rather than appearing overnight. In one study of parotid gland cancers, patients had symptoms for an average of 12 months before diagnosis, with some cases stretching to 10 years.
Certain cancer types are more likely to involve the facial nerve than others. Adenoid cystic carcinoma caused facial nerve problems in 60% of cases, and squamous cell carcinoma in 66%. Any facial weakness that worsens progressively rather than appearing suddenly warrants imaging to rule out a mass.
Stroke
Stroke can cause facial weakness, but the pattern looks different from Bell’s palsy in a way that’s clinically important. In a stroke, the forehead is typically spared. You can still raise your eyebrows and wrinkle your forehead on the affected side, but the lower face droops. This happens because the forehead muscles receive nerve signals from both sides of the brain, so damage to one side still leaves the forehead functional.
With Bell’s palsy and other causes that damage the facial nerve itself, the entire half of the face is affected. You lose the forehead crease, the eyebrow drops, and you can’t close the eye on that side. This forehead-sparing distinction is one of the first things evaluated in an emergency room to determine whether facial weakness is coming from the brain or from the nerve.
There is one exception worth noting. Certain small strokes in the brainstem (pontine strokes) can mimic Bell’s palsy by producing full-face paralysis including the forehead. These are uncommon but can fool even experienced clinicians, which is why sudden facial paralysis accompanied by other neurological symptoms like limb weakness, slurred speech, or difficulty with balance is treated as a potential stroke.
Autoimmune Conditions
Guillain-Barré syndrome, a condition where the immune system attacks the protective coating of nerves, can target both facial nerves simultaneously. A specific subtype called bifacial weakness with paresthesias produces rapid bilateral facial paralysis along with tingling sensations, but without the limb weakness or walking difficulties that characterize the more common forms of Guillain-Barré. This subtype is caused by demyelination, meaning the immune system strips the insulating layer off the nerve fibers rather than destroying the fibers themselves, which generally allows for better recovery.
Congenital Facial Paralysis
Some children are born with facial paralysis. Moebius syndrome is the most recognized congenital cause, involving underdevelopment or absence of the facial nerve (and often the nerve controlling eye movement). Most cases appear sporadically with no family history, though rare familial cases follow an autosomal dominant inheritance pattern, meaning a parent with the condition has a 50% chance of passing it on. The familial form tends to be milder and more often affects just one side, without the additional birth differences that sometimes accompany sporadic cases.
How Severity Is Measured
Doctors grade facial paralysis on a six-point scale. Grade I is normal function. Grade II is mild weakness noticeable only on close inspection, with the eye still closing easily. Grade III involves obvious asymmetry between the two sides of the face but the eye can still close with effort. At Grade IV, the forehead no longer moves and the eye doesn’t fully close. Grade V means barely perceptible movement with visible asymmetry even at rest. Grade VI is total paralysis with no movement at all. This grading helps guide treatment decisions and track recovery over time.
Middle Ear Infections and Surgery
Chronic or severe middle ear infections can spread inflammation to the facial nerve as it passes through the temporal bone near the middle ear cavity. The nerve runs remarkably close to the structures of the middle ear, making it vulnerable when infection erodes the thin bone separating them. Surgery on the parotid gland also carries a recognized risk of facial nerve injury, since the nerve runs directly through the gland. Surgeons carefully map the nerve during these procedures, but temporary weakness afterward is not unusual, and permanent damage occurs in a small percentage of cases.