Facial nerves
Bell's palsy is believed to occur when the nerve that controls the facial muscles becomes compressed Wiki Commons

Australian businesswoman and socialite Roxy Jacenko is the latest celebrity to be diagnosed with Bell's Palsy, a rare condition which mimics the symptoms of a stroke and affects around one in 5,000 of the world's men and women every year.

Jacenko, who appeared on The Celebrity Apprentice Australia, posted a headless photograph of herself and her daughter Pixie on Instagram - a clue to the effects of the condition.

She wrote the caption: "Headless shots for the moment - with my buddy @pixiecurtis - bells palsy is something I hadn't even heard of till now. Let's hope I shake it soon."

But what is Bell's Palsy?

The conditon, first identified by Scottish clinicial Sir Charles Bell in the 19th Century, causes temporary weakness or paralysis of the muscles in one side of the face. Although the condition is rare, it is the most common cause of facial paralysis.

The symptoms vary from person to person, but in general, the weakness on one side of the face can be described as either partial palsy, or complete palsy. No movement at all can be felt in complete palsy, which is the rarer form of the condition.

Bell's Palsy can also affect the eyelid and mouth, which makes it difficult for the patient to open and close them. In extremely rare cases, the palsy can affect both sides of the face.

However, facial weakness or paralysis is a sign of a stroke, a more serious condition. A doctor may also check for lyme disease, a bacterial infection caused by ticks, moebius syndrome, a rare congenital condition, a middle ear infection, head injury or cholesteatoma, an abnormal collection of skin cells in the middle ear.

Why does it happen?

Bell's Palsy is believed to occur when the nerve that controls the facial muscles becomes compressed.

The facial nerve passes through a narrow gap of bone near the upper jaw on its way from the brain to the face. If the facial nerve is compressed or swollen it can interfere with the signals that your brain sends to the muscles in your face.

This can restrict the blood and oxygen supply to the nerve cells, which causes the facial weakness or paralysis.

Men and women are affected equally, but Bell's Palsy is more common in pregnant women and those with diabetes and HIV - although the reasons for this are not yet understood.

The herpes virus, as well as other viral infections, is thought to occasionally contribute to inflammation of the facial nerve. It is believed to occur as a complication of pneumonia, although this is rare.

How long is recovery?

Around seven out of 10 people make a complete recovery, with or without treatment. Normally, the symptoms fade after two or three weeks, but a complete recovery can take up to six months.

John Sudworth, a BBC reporter, detailed his slow recovery from the condition over the course of one year.

Steroids, usually prednisolone, are used to reduce the swelling of the facial nerve. In addition, eye drops may be used if the eye is unable to close.

However, around two in 10 patients will be left with more significant problems, such as a reduced sense of taste and permanent tensing of the facial muscles.