One-sided facial drooping is most commonly caused by Bell’s palsy, a sudden weakness of the facial nerve that affects roughly 40,000 Americans each year. But it can also be the first visible sign of a stroke, which makes it critical to rule that out quickly before considering other explanations. The distinction between the two often comes down to a few specific details about where the drooping occurs and what other symptoms are present.
Stroke or Bell’s Palsy: How to Tell the Difference
The single most important thing to assess when one side of your face droops is whether you’re having a stroke. The BE-FAST acronym covers the warning signs: Balance problems, Eye changes, Facial weakness, Arm weakness, Speech difficulties, and Time to call emergency services. If facial drooping appears alongside arm weakness, slurred speech, sudden vision changes, or difficulty walking, call 911 immediately. Stroke treatment is time-sensitive, and every minute matters.
If the drooping is isolated to the face, a key clue lies in the forehead. Bell’s palsy affects the entire half of the face, including the forehead. You won’t be able to raise your eyebrow or wrinkle your forehead on the affected side. A stroke typically spares the forehead because the muscles there receive nerve signals from both sides of the brain. So if your forehead still moves normally but the lower face droops, that pattern is more consistent with a stroke than Bell’s palsy.
Another distinguishing detail: Bell’s palsy does not cause numbness. The face feels weak and may look dramatically different, but sensation remains intact. Stroke often produces a loss of feeling on the affected side, along with symptoms in other parts of the body.
What Bell’s Palsy Actually Is
Bell’s palsy is an inflammation of the seventh cranial nerve, the nerve responsible for controlling all the muscles of facial expression. This nerve travels through a narrow bony canal in the skull near the ear. When the nerve swells inside that tight space, it gets compressed, and the signals to your facial muscles are partially or completely blocked.
The result is striking. The corner of the mouth droops. Skin folds on the affected side flatten out. The forehead appears smooth and unwrinkled. The eyelid won’t close fully, and the lower lid may sag, allowing tears to spill down the cheek. Some people also experience hyperacusis, where sounds seem uncomfortably loud in one ear, because a tiny muscle inside the ear that normally dampens vibrations is also controlled by the same nerve.
The leading cause appears to be reactivation of the herpes simplex virus (the same virus responsible for cold sores). Research has found that this virus lies dormant in nerve tissue near the ear, and in Bell’s palsy patients, it reactivates and triggers inflammation. The evidence for this link is strong enough that some researchers have proposed renaming Bell’s palsy to “herpetic facial paralysis.”
Other Causes of Facial Drooping
Ramsay Hunt syndrome is a related condition caused by the varicella-zoster virus, the same virus behind chickenpox and shingles. It produces facial paralysis similar to Bell’s palsy but with one distinguishing feature: a painful, blistering rash on or around the ear, inside the ear canal, or sometimes on the tongue and roof of the mouth. Ramsay Hunt syndrome tends to be more severe than Bell’s palsy, with lower rates of full recovery.
Lyme disease is another cause worth knowing about, especially if you live in or have visited areas where tick-borne illness is common. About 9 out of every 100 reported Lyme disease cases involve facial palsy. A distinctive clue is that Lyme can cause drooping on both sides of the face, which is unusual for Bell’s palsy. If you develop facial weakness along with a recent tick bite, a bull’s-eye rash, fever, or joint pain, Lyme disease should be on the radar.
Treatment and the 72-Hour Window
For Bell’s palsy, the timing of treatment matters. Guidelines recommend starting steroid therapy within 72 hours of symptom onset for the best chance of full recovery. For mild to moderate cases, steroids alone appear to be the most effective approach. For severe cases where the face is completely paralyzed, adding antiviral medication to steroids may reduce the risk of long-term complications like synkinesis, a condition where nerves regrow incorrectly and cause unintended movements (like your eye twitching when you smile).
This means you shouldn’t wait to see if things improve on their own. Getting evaluated within the first day or two gives you the widest treatment window.
Protecting Your Eye
One of the most immediate concerns with facial paralysis is the eye on the affected side. When you can’t blink or fully close your eyelid, the surface of the eye dries out quickly, putting you at risk for corneal damage. Three measures help protect it: artificial tears or lubricating ointment to keep the eye moist, tape or adhesive strips to hold the eyelid closed during sleep, and glasses or protective eyewear during the day to shield the eye from wind and debris. This isn’t optional. Corneal abrasions can cause lasting vision problems if the eye goes unprotected.
Recovery Timeline
Most people with Bell’s palsy recover well. About 75% reach full recovery within one year, and that number climbs to roughly 83% by the two-year mark. Recovery typically begins within a few weeks, with gradual improvement over months. The first signs are usually subtle: a flicker of movement in the eyelid, a slight return of the smile.
However, about 25% of patients end up with some degree of lasting facial asymmetry or complications. Synkinesis is the most common long-term issue. It happens when regenerating nerve fibers connect to the wrong muscles, so voluntary movements on one side of the face trigger involuntary movements elsewhere. For example, smiling might cause the eye to squint, or chewing might make the eye water (sometimes called “crocodile tears”).
Facial Exercises and Rehabilitation
Physical therapy focused on facial neuromuscular retraining is the most studied rehabilitation approach. The core techniques are surprisingly simple: practicing specific facial movements in front of a mirror, using the visual feedback to retrain the brain’s connection to the recovering muscles. This is sometimes called “mime therapy” and involves slow, deliberate movements like raising the eyebrows, closing the eyes gently, and smiling symmetrically.
Mirror biofeedback, where you watch your own face carefully while performing exercises, helps you identify and correct asymmetric movements as they develop. Some clinics also use electromyographic biofeedback, which provides a readout of muscle activity so you can see which muscles are firing. Daily home practice of about 30 minutes has been shown to help, and physical rehabilitation appears to be particularly effective at preventing synkinesis in younger patients and women. Starting exercises early, with guidance from a therapist who specializes in facial rehabilitation, gives the best outcomes.