Bell's palsy - Causes of Bell's palsy
NHS Choices Medical Reference
Bell's palsy occurs when the nerve that controls the facial muscles (facial nerve) becomes inflamed or compressed. It is not known what causes the facial nerve to become inflamed, although it is thought that a virus, possibly a herpes virus, may be responsible.
The facial nerve
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 interference can restrict the blood and oxygen supply to your nerve cells and cause the facial weakness or paralysis that is characteristic of Bell's palsy.
The types of herpes virus thought to cause inflammation of the facial nerve are:
- the herpes simplex virus (HSV), including either herpes type 1 (HSV-1), which causes cold sores, or herpes type 2 (HSV-2), which causes genital herpes
- the varicella-zoster virus, which causes chickenpox and shingles
The varicella-zoster virus is a less common cause of Bell's palsy than the herpes simplex virus, but can lead to the more serious condition called Ramsay Hunt Syndrome.
Read more about complications of Bell's palsy.
In addition to herpes, Bell's palsy has also been linked with other viral infections.
As a complication of pneumonia
Bell's palsy is thought to occasionally occur as a complication of pneumonia.