Bell's palsy - Causes of Bell's palsy

Bell’s palsy occurs when the nerve that controls the facial muscles (facial nerve) becomes inflamed or compressed.

It's not known what causes the facial nerve to become inflamed, although it's 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.

Herpes virus

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.

Other viruses

In addition to herpes, Bell's palsy has been linked with many other viral infections, such as:

• Lyme disease
• syphilis
• the Epstein-Barr virus – which causes glandular fever
• cytomegalovirus

Other risk factors

People with diabetes and HIV are thought to be at a higher risk of developing Bell's palsy, although the reason for this is not fully understood.