Nobody knows for sure what ultimately causes Bell’s palsy, the mysterious nerve condition that paralyzed half of Angelina Jolie’s face. Likewise, there’s no strong consensus on how to treat it. But doctors aren’t completely in the dark: They have a general idea of how to diagnose it and what its symptoms are, and they have some ideas on how it can be treated.

In her recent cover story in the September issue of Vanity Fair, Jolie reveals that she was diagnosed with Bell’s palsy last year.

“Sometimes women in families put themselves last,” she said in the interview, “until it manifests itself in their own health.” Jolie reports that the condition caused half of her face to droop, a symptom that is fairly common among Bell’s palsy patients.

Bell’s palsy, which can cause paralysis in one side of a person’s face, occurs when the facial nerve — also known as the 7th cranial nerve — becomes inflamed. This nerve, which passes through a narrow tunnel in the skull, carries motor signals from the brain to facial muscles and sensory signals from the face to the brain. If, for some reason, this nerve swells (possibly due to inflammation), it can become compressed inside its tight quarters. When this happens, the signals it carries might not reach where they should be going. This accounts for some of the most noticeable symptoms of Bell’s palsy: drooling, facial drooping, and difficulty moving facial muscles on one side.

Many patients also experience tongue numbness, a metallic taste in the mouth, and irritation in one eye from not being able to close it all the way.

Image from page 160 of "Surgical treatment; a practical treatise on the therapy of surgical diseases for the use of practitioners and students of surgery" (1920)
Bell's palsy occurs due to an inflammation of the facial nerve, but doctors aren't sure what causes the inflammation.

And while the root cause of the facial nerve inflammation associated with Bell’s palsy is not totally clear, Jolie may be correct in her assessment that stress can bring on the condition. One of the possible explanations for Bell’s palsy is that it’s caused by herpes simplex virus — the virus that can cause either cold sores or genital herpes, depending on the type. This virus, which can remain dormant in a person’s nervous system, sometimes becomes active during times of stress.

But herpes simplex isn’t the only suspect standing in the Bell’s palsy lineup. Doctors also hypothesize that it could be caused by brain tumors, Lyme disease, mononucleosis, and herpes zoster — the virus that can cause shingles, chicken pox, and Ramsay Hunt syndrome. There is no direct test for Bell’s palsy, so doctor typically use differential diagnosis, ruling out the possible causes that could require urgent medical interventions.

bell's palsy
A person with Bell's palsy often experiences paralysis in half their face, making it difficult to move their lips or eyelids.

Because doctors aren’t certain about the root cause of Bell’s palsy, treatments vary pretty widely. Jolie credits acupuncture — a fairly common treatment for the condition — for her recovery. But there aren’t any controlled trials to confirm that it is any more effective than placebo or no treatment at all. Most cases of Bell’s palsy will resolve in a month or so with no treatment.

There is always the possibility of lasting symptoms, though, and some treatments could help reduce their risk. The American Academy of Neurology’s treatment guidelines say that, “For patients with new-onset Bell’s palsy, steroids are highly likely to be effective and should be offered to increase the probability of recovery of facial nerve function.”

Prescribing a steroid such as prednisone is common, as its anti-inflammatory properties could help take pressure off the facial nerve. If the nerve becomes so inflamed that it gets frayed inside its canal, the connections within it could become permanently damaged. When the inflammation subsides, this could even result in some crossed signals if unrelated nerves accidentally form new connections. This means that a person’s cheek may twitch when they blink or their eye may water when they salivate. Treating the condition early and aggressively with steroids seems to reduce this risk.

Another treatment is valcyclovir — more commonly known by its brand name, Valtrex. There is evidence that this herpes drug can help improve outcomes for Bell’s palsy patients, lending credence to the herpes hypothesis.

So even though we don’t know for sure what causes Bell’s palsy, you should definitely seek medical care if you experience facial paralysis in case it turns out to be something more serious. If you do have Bell’s palsy, follow your doctor’s treatment plan, and like Angelina Jolie, you’ll probably make a full recovery.