What is Ramsay Hunt syndrome, the condition affecting Justin Bieber

Justin Bieber has revealed that he is suffering from a rare condition that has paralyzed one side of his face.

Earlier this week, the Canadian singer canceled a number of upcoming shows because of illness, and on Friday he told fans he has been diagnosed with Ramsay Hunt syndrome.

"It is from this virus that attacks the nerve in my ear and my facial nerves, and has caused my face to have paralysis," the 28-year-old singer said in an Instagram video.

"As you can see, this eye is not blinking. I can't smile on this side of my face. This nostril will not move."

What is Ramsay Hunt syndrome?

Ramsay Hunt syndrome is a rare neurological disorder that can occur in people who were previously infected with chickenpox.

If the dormant varicella-zoster virus is reactivated, leading to shingles, it can affect the facial nerve and may lead to facial paralysis and hearing loss.

Symptoms of the condition can include blisters in the ears or the roof of the mouth.

According to the National Organization for Rare Disorders (NORD), Ramsay Hunt syndrome is rare - affecting about 5 in 100,000 people in the United States, according to one estimate. Older adults are more likely to be affected.

How is it Ramsay Hunt syndrome diagnosed and treated?

The syndrome is usually diagnosed through a detailed medical history and identifying the characteristic rash and facial paralysis.

This can be difficult, however, as symptoms may not appear at the same time, according to NORD. In some cases, the rash may be completely absent, the Mayo Clinic says.

Once Ramsay Hunt syndrome is diagnosed, antivirals and steroids are recommended.

How severe is Ramsay Hunt syndrome?

According to British charity Facial Palsy UK, prompt treatment can make a significant difference to a patient's outcome, with about 70% of those who receive antiviral medication within three days of developing symptoms making a full recovery.

If this does not happen, the chances of a complete reversal of symptoms falls to 50%.

Mild cases can resolve within a few weeks, the charity says, but more severe damage to the nerve leads to a longer recovery time and lower chances of a complete return to health.

Bieber has said he is focusing on resting and doing facial exercises to help his recovery: "It will go back to normal - it's just time, and we don't know how much time that's going to be."