Bell’s palsy happens when the facial nerve, which controls the muscles on one side of your face, becomes inflamed and swollen. This swelling compresses the nerve inside a narrow bony channel in your skull, disrupting the signals that let you smile, blink, and move your forehead. About 23 out of every 100,000 people develop it each year, and it strikes without much warning.
What Triggers the Nerve Inflammation
The leading theory points to viral reactivation. Herpes simplex virus type 1 (the same virus behind cold sores) is considered one of the major causes. Most people carry this virus without knowing it. It stays dormant in nerve tissue for years or decades, then reactivates under certain conditions, triggering inflammation in and around the facial nerve.
The varicella-zoster virus (the one responsible for chickenpox and shingles) can also cause facial paralysis, sometimes without producing any visible skin rash. Other viruses in the herpes family, including Epstein-Barr virus and cytomegalovirus, have been linked to Bell’s palsy as well. In many cases, the exact trigger is never identified.
There’s also evidence that the immune system itself plays a role. A viral infection or reactivation may provoke an autoimmune reaction where the body’s immune cells mistakenly attack the protective coating (myelin) around the facial nerve. This process, called demyelination, disrupts the nerve’s ability to transmit signals. Some researchers consider Bell’s palsy a cranial nerve variant of Guillain-Barré syndrome, a condition where the immune system damages peripheral nerves throughout the body. Whether the virus directly injures the nerve or simply sets off a misguided immune response, the end result is the same: the facial nerve swells inside its bony canal and stops working properly.
Who Is Most at Risk
Bell’s palsy can affect anyone at any age, but certain groups face higher odds. Diabetes is an independent risk factor, present in more than 10% of adults who develop Bell’s palsy. The connection likely relates to how diabetes damages small blood vessels and nerves over time, making the facial nerve more vulnerable to inflammation.
Pregnant women, particularly in the third trimester and the first week after delivery, develop Bell’s palsy at higher rates than the general population. Hormonal shifts and fluid retention during late pregnancy may increase pressure on the nerve within its tight bony passage. People with upper respiratory infections (colds or flu) also appear more susceptible, which fits with the viral reactivation theory.
A rare familial form of recurrent Bell’s palsy does exist. It follows an autosomal dominant inheritance pattern, meaning a parent with the genetic mutation has a 50% chance of passing it to each child. This familial version is uncommon, but if multiple relatives have experienced facial paralysis, genetics may be a contributing factor.
How Symptoms Develop
The hallmark of Bell’s palsy is speed. Facial weakness appears suddenly, often overnight or over just a few hours. You might wake up unable to close one eye, notice drooling on one side of your mouth, or find that half your face feels stiff and unresponsive. Symptoms typically reach their peak severity within 48 to 72 hours.
The paralysis only affects one side of the face. Because the facial nerve also carries taste signals and helps control tear production, you may notice a loss of taste on the front two-thirds of your tongue, excessive tearing or dryness in one eye, and heightened sensitivity to sound in the affected ear. Pain behind the ear or along the jaw on the affected side often shows up a day or two before the paralysis itself, though not everyone experiences this warning sign.
How It Differs From a Stroke
Because Bell’s palsy causes sudden facial drooping, many people initially fear they’re having a stroke. The key difference is which part of the face is affected. Bell’s palsy involves the entire half of the face, including the forehead. You won’t be able to raise the eyebrow on the affected side. A stroke typically spares the forehead because of how the brain’s motor pathways are wired, so forehead movement remains intact even when the lower face droops. A stroke also usually comes with additional symptoms like arm weakness, slurred speech, or confusion. If you’re unsure, treat it as an emergency until proven otherwise.
Recovery and What to Expect
The good news is that most people recover without lasting damage. Between 66% and 85% of patients experience complete spontaneous recovery within three to eight weeks. Children under 14 and pregnant women fare even better, with recovery rates approaching 90%.
More than two-thirds of all patients regain full facial function on their own. For the remaining third, recovery may be partial or take longer. Some people develop synkinesis, where nerve fibers regrow along the wrong paths. This can cause involuntary movements, like your eye closing when you smile, or your cheek twitching when you blink. These complications are more common when the initial paralysis was severe.
Treatment started early (ideally within 72 hours of symptom onset) can improve outcomes. A short course of oral corticosteroids reduces nerve swelling and is the most widely supported treatment. Protecting the eye on the affected side is also important during recovery, since an inability to blink fully can dry out the cornea. Lubricating eye drops during the day and taping the eye shut at night help prevent damage.
Bell’s palsy recurs in about 7% to 12% of people, sometimes on the same side and sometimes on the opposite side. Recurrence is more common in those with a family history or with diabetes. Most recurrent episodes also resolve well, though the recovery timeline may be slightly longer with each occurrence.