What is it?
Bell's palsy is a one-sided loss of function in the facial nerve, the nerve that works the muscles of expression. What is lost is power, not sensation: the eyebrow will not lift, the eye does not close fully, the corner of the mouth drops and you cannot whistle. The cheek feeling numb comes from the muscles not working.
The first sentence of this page has to be a warning. In anyone whose face has dropped suddenly, a stroke is ruled out first. In Bell's palsy the forehead is affected too and the eyebrow cannot be raised, while in a stroke the forehead is most of the time spared. Neither you nor the person with you can make this distinction; it is made in hospital by examination and, where needed, by scans.
In Bell's palsy the symptoms settle in over hours and generally reach their worst point within one to three days. The nerve becoming squeezed by swelling inside a narrow bony canal is held responsible. Marked improvement is expected in most people, but because starting treatment in the first few days affects the outcome, no time should be lost.
Signs
You will not necessarily have all of these at once.
Why does it happen?
- 01
A virus reactivating at the nerve root
The mechanism dwelt on most is a virus from the cold sore family waking up in a nerve ganglion. The reactivation makes the nerve swell, and the nerve is then squeezed inside its narrow bony canal.
- 02
Compression caused by swelling
The facial nerve passes through a narrow bony canal at the base of the skull. A swollen nerve finds no room to expand there and conduction stops; this is why the symptoms settle in within hours.
- 03
Other conditions that produce a similar picture
Shingles in the ear, a middle ear infection, tick-borne infections, injury, diabetes and growths in the area can all look the same. Bell's palsy is only named once these have been ruled out.
- 04
Factors thought to prepare the ground
Tiredness, lack of sleep, heavy stress, pregnancy and exposure to cold are commonly reported. There is no proof that these cause it directly; they are counted as predisposing factors.
How does it progress?
- First 72 hours
The settling-in period
The loss of power increases quickly and reaches its worst point. This is also the window in which the treatment decision has to be made, so seeking help is not delayed.
- 1–3 weeks
The static period
The face is largely motionless. Because the eye does not close, the risk of a dry and damaged cornea is highest in this period; eye care must not be neglected.
- 3 weeks–3 months
Movement starting to return
In most people muscle movement comes back piece by piece. The eyebrow and the area around the eye come first, then movement at the corner of the mouth becomes clearer.
- After 3 months
Period of residual findings
In some people mild asymmetry, accompanying movements such as the corner of the mouth pulling when the eye closes, or a watering eye while eating can remain.
How is it treated?
A dentist does not treat this condition. When one side of your face drops, the place to go the same day is an emergency department or a neurology clinic. There are two reasons for the urgency: ruling out a stroke, and starting drug treatment within the first few days. The clinic's job is to recognise the picture, record the time your symptoms started and refer you without losing time.
In hospital a neurological examination is carried out, the ear and ear canal are checked for a shingles rash, and scans are requested where needed. The treatment decision belongs to the doctor; a corticosteroid may be started early, and in selected cases an antiviral drug may be added. Do not take medication on your own decision and do not stop the treatment you have been given part way through.
The eye that will not close is a separate heading, and the cornea can be damaged if it is neglected. Artificial tears, covering the eye at night and protection from the wind are used as your doctor describes. During recovery, facial exercises and physiotherapy may be recommended. Night guards, painkillers and dental procedures used in a dental clinic have no place in this condition.
- Facial drooping together with weakness in an arm, disturbed speech or loss of balance
- Being able to wrinkle the forehead normally, that is, the eyebrow lifting easily on the affected side
- Severe headache, fever, a stiff neck or confusion alongside it
- Blisters on the outer ear, severe ear pain or sudden hearing loss
How is it prevented?
- Note the time the moment you notice asymmetry in your face; when your symptoms started is used directly in the treatment decision.
- Do not tape the eye that will not close using a method of your own; learn from your doctor how eye care should be done and keep it up.
- Keep up your diabetes and blood pressure checks; uncontrolled diabetes can affect both the risk and the recovery.
- If there is ear pain, blistering or a change in your hearing, tell the doctor about it separately; this finding can change the treatment plan.
Frequently asked questions
- Can I work out at home whether this is a stroke or Bell's palsy?
- No. There are distinguishing findings, such as forehead movement, but these are examination findings and are not enough on their own to decide. Everyone whose face drops suddenly needs to be assessed in hospital the same day; waiting can cost time that cannot be got back.
- Will my face go back to how it was?
- Marked improvement is expected in most people, but how long it takes and how far it goes varies from person to person and cannot be said in advance. In some people mild asymmetry or accompanying involuntary movements can remain. Treatment started early and regular follow-up matter in this process.
- Can dental treatment cause facial palsy?
- After an anaesthetic in the lower jaw, the solution can reach branches of the facial nerve and cause a temporary facial weakness lasting a few hours; this settles once the anaesthetic wears off. It should not be confused with a facial palsy that comes on by itself and lasts for days, and in both cases you should let your dentist know.
This content is for general information and does not replace an in-person examination. Symptoms overlap between conditions, and a diagnosis can only be made clinically.