Bell's palsy explained: sudden facial weakness

Stroke first: why urgent assessment matters

Before anything else, the most important message is this: sudden weakness or drooping of the face can be a sign of a stroke, which is a life-threatening emergency, and it is not safe to assume it is Bell's palsy. Use the FAST test — Face: has their face drooped on one side, can they smile? Arms: can they raise both arms and keep them there? Speech: is it slurred or muddled? Time: if you see any of these signs, call 999 immediately. A key clue is that in a stroke, other parts of the body, such as an arm or the speech, are often affected too, whereas Bell's palsy affects only the face. But you should never try to make this judgement yourself — always seek urgent assessment.

What Bell's palsy is

Bell's palsy is a weakness or paralysis of the muscles on one side of the face, caused by a problem affecting the facial nerve, which controls those muscles. It usually comes on quickly, over hours to a day or two. The exact cause is not fully understood, but it is thought to involve swelling and inflammation of the nerve, possibly triggered by a viral infection. It can happen to anyone, at any age, and is more common in pregnancy and in people with diabetes. A useful distinguishing feature is that Bell's palsy typically affects the whole of one side of the face, including the forehead, so the person often cannot wrinkle their forehead or close the eye on the affected side — something that tends to be spared in a stroke.

Symptoms to look out for

The main symptom is a rapid weakening or drooping of one side of the face. This can make the mouth droop, cause drooling, and prevent the eye on that side from closing fully. People may find it hard to smile, eat or drink on that side, and speech can sound slightly slurred because the lips do not move normally. Other symptoms can include a dull ache around the jaw or behind the ear, increased sensitivity to sound in one ear, changes to taste, and a dry or watery eye. Because the eye may not close properly, it can become dry and is at risk of damage, which is why protecting it is an important part of care. Symptoms usually reach their worst within a couple of days.

Diagnosis and treatment

Bell's palsy is usually diagnosed from the story and an examination, once a stroke and other causes have been considered and ruled out. There is no single test for it; instead, the doctor checks the pattern of facial weakness and looks for other symptoms that might point to a different cause. Treatment works best when started early, ideally within the first few days, which is another reason to seek help promptly. A short course of steroid medicine is commonly used to reduce inflammation of the nerve and improve the chances of full recovery. Looking after the affected eye is essential — using lubricating drops, and taping or covering the eye at night if it will not close — to prevent it drying out and being harmed.

Recovery and outlook

The outlook for Bell's palsy is generally good. Most people begin to improve within two to three weeks and go on to make a full or nearly full recovery over several weeks to a few months, particularly with early treatment. A smaller number are left with some lasting weakness or other longer-term effects, and occasionally the face recovers with some altered movements. If there is no sign of improvement after about three weeks, or if symptoms are unusual, further assessment may be needed to look for another cause. Throughout recovery, continuing to protect the eye remains important. While Bell's palsy can be distressing to live through, it helps to remember that the great majority of people recover well.