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One-sided facial weakness
Category: Brain & Nerves · All brain & nerves symptoms
What it can feel like
One-sided facial weakness means one side of the face droops — the smile is uneven, the eye may not close fully, and sounds may seem loud in that ear. It has two big causes with very different urgency: Bell's palsy (the facial nerve itself) and stroke (the brain) — the forehead is the clue that separates them.
Possible causes
A symptom can have many causes, and most are not serious. The lists below group conditions this symptom can be associated with — common causes first. They are possibilities to discuss with a clinician, not a diagnosis.
Common causes
Facial weakness can be associated with Bell's palsy — inflammation of the facial nerve, often viral — in which the whole side including the forehead is weak, sometimes with pain behind the ear and taste changes.
Other possible causes
Facial weakness can also be associated with stroke, in which the forehead usually still moves (it has a backup supply from both sides of the brain), and with shingles affecting the ear (with blisters), Lyme disease, and tumours of the parotid gland or nerve.
Red flags — when to seek help promptly
- Facial weakness with arm or leg weakness, speech problems or onset over minutes — emergency (possible stroke)
- Facial weakness with blisters in or around the ear
- Facial weakness that develops slowly over weeks, or keeps recurring
- An eye that cannot close, becoming dry, red or painful
- Facial weakness after a head injury or ear surgery
What a clinician may do
Emergency assessment is used whenever stroke is possible. For Bell's palsy, a clinician examines the ear and parotid gland, tests eye closure, and starts corticosteroids promptly when appropriate — eye protection (lubrication and taping at night) prevents corneal damage while the nerve recovers.
Watch: related videos
Examination and clinical videos from the MedicalVideos.com library relevant to this symptom. Some clinical footage is graphic — that is the nature of a medical video library.
Related guides on MedicalVideos.com
Frequently asked questions
Why does the forehead matter?
The forehead muscles receive signals from both sides of the brain, so a stroke usually spares forehead movement while the lower face droops. A facial-nerve problem (Bell's palsy) takes the whole side, forehead included. That one observation, made in seconds, triages the case.
Does Bell's palsy recover?
Most people recover fully or nearly so, especially with early steroid treatment. Recovery takes weeks to months as the nerve heals. Protecting the eye that cannot close is the crucial task meanwhile.
Related symptoms — Brain & Nerves
Browse the O section of the A–Z list or return to the Symptoms A–Z hub.