What Causes Bell’s Palsy? Common Risk Factors Explained

Bell’s palsy can be an alarming diagnosis because it causes sudden weakness or paralysis on one side of your face. Certain infections, health conditions, and other factors may trigger inflammation of your facial nerve. Learning about these possible causes can help you better understand why Bell’s palsy develops and what it may mean for your recovery. 

What is Bell’s palsy?

Bell’s palsy is a medical condition that causes sudden weakness or paralysis on one side of your face. 

Other conditions can also cause one-sided facial weakness and paralysis including:

• Lyme disease

• Ramsay Hunt syndrome

• Stroke

• Multiple sclerosis (MS)

• A tumor affecting the facial nerve

It’s important to get medical care right away if you develop sudden facial weakness or paralysis. Your healthcare team can determine whether you have Bell’s palsy or another condition that needs different treatment.

Experts still don’t know what causes Bell’s palsy. But research shows that some health conditions are linked to a higher chance of developing it. These conditions don’t directly cause Bell’s palsy. But they may make it more likely to happen. Here are five conditions that may raise your risk of Bell’s palsy.

1. Herpes simplex virus (HSV‑1)

Herpes simplex virus type 1 (HSV-1) is a common virus best known for causing cold sores. It’s the most common trigger for Bell's palsy. But experts haven't proven that it directly causes the condition. 

Researchers think the virus may "wake up" after staying inactive in the body for years. This may lead to swelling around the facial nerve, which can affect the muscles on one side of your face. But since HSV-1 is very common, while Bell’s palsy is rare, experts think other factors may also play a role. Researchers are still studying why only some people with HSV-1 develop Bell’s palsy. 

2. Varicella zoster virus (VZV)

Varicella-zoster virus (VZV) is another type of herpes virus. It’s best known for causing chickenpox and shingles. Researchers think it may also play a role in some cases of Bell’s palsy. But they haven’t been able to prove this yet.

When VZV causes shingles that affects the facial nerve, it can lead to facial paralysis and a painful rash. This condition is called Ramsay Hunt syndrome. Researchers know that VZV is the cause of this syndrome.

But VZV doesn’t always cause a rash. Researchers think the virus can sometimes affect the facial nerve without causing visible skin changes. When this happens, the symptoms can look just like Bell’s palsy. This means some people diagnosed with Bell’s palsy may actually have a VZV infection. Healthcare professionals aren’t always able to prove that these people have a VZV infection because testing isn’t always easy to do. 

But this is one reason healthcare professionals often prescribe antiviral medication along with steroids for some people with Bell’s palsy.

3. Diabetes

People with diabetes are more likely to develop Bell’s palsy than people without diabetes. But diabetes doesn’t directly cause Bell’s palsy. 

Instead, researchers think it may make the facial nerve more sensitive to injury. Diabetes can reduce blood flow to nerves and may also make it easier for viruses like HSV-1 to become active again. Together, these changes may raise the risk of Bell’s palsy and slow recovery in some people. 

4. Pregnancy

Some research suggests that Bell’s palsy is more common during pregnancy, especially in the last few months of pregnancy and the first few weeks after giving birth. But pregnancy doesn’t directly cause Bell’s palsy. Instead, researchers think the changes that happen during pregnancy may make the facial nerve more vulnerable to injury. These changes include a weaker immune response, more fluid in the body that can put pressure on the facial nerve, and conditions like preeclampsia or gestational diabetes. Together, these changes may raise the risk of Bell’s palsy in some pregnant people. 

5. Common cold viruses

Some people develop Bell’s palsy shortly after having a cold, the flu, or another upper respiratory infection. But common cold viruses and the flu don’t appear to directly cause Bell’s palsy. Instead, researchers think these illnesses create the right conditions for Bell’s palsy to develop. For example, HSV-1 may become more active again while your immune system is busy fighting a cold or the flu. This may trigger swelling around the facial nerve. Inflammation from a cold or flu may also make your facial nerve more vulnerable to injury. Together, these changes may raise the risk of Bell’s palsy. 

What are the symptoms of Bell’s palsy?

Bell’s palsy usually affects one side of your face. Symptoms include:

• Weakness or paralysis on one side of your face

• Trouble smiling or making facial expressions

• Difficulty closing one eye

• Drooling

• Headache

• Changes in your sense of taste

• Sounds seeming louder than usual in one ear

• Changes in tear or saliva production

In rare cases, Bell’s palsy can affect both sides of your face.

How do you diagnose Bell’s palsy?

There’s no specific test that can diagnose Bell’s palsy. Your healthcare team can diagnose it by ruling out other conditions that can cause sudden facial weakness or paralysis, like stroke or Lyme disease. 

Your team will ask about your symptoms, review your medical history, and examine your face to see how well your facial muscles work. Depending on your symptoms, they may also order blood tests or imaging tests, such as an MRI or CT scan. These tests look for other possible causes, like Lyme disease, a stroke, or a tumor. If no other cause is found, your healthcare team may diagnose you with Bell’s palsy. 

How do you treat Bell’s palsy?

There’s no cure for Bell’s palsy, but symptoms often start to get better within a few weeks. For many people, symptoms go away completely over the next 3 to 6 months. 

Your healthcare team may recommend treatments to help speed recovery, ease symptoms, and protect your face while the facial nerve heals. These treatments may include:

• Corticosteroids: These medicines help reduce swelling around your facial nerve. 

• Antiviral medication: Medicines like acyclovir or valacyclovir may be helpful for some people.

• Pain relievers: Over-the-counter (OTC) medicines like acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) can help relieve pain.

• Eye care: Artificial tears and lubricating eye ointment can help protect your eye if you can’t fully close your eyelid.

• Facial exercises: Facial exercises to help improve facial movement as you recover.

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Written by:

Nishika Reddy, MD

Nishika Reddy, MD, is an attending physician at the University of Utah. She provides comprehensive and cornea medical care at the Moran Eye Center and serves as clinical assistant professor.

Edited by:

Patricia Pinto-Garcia, MD, MPH

Patricia Pinto-Garcia, MD, MPH, is a medical editor at GoodRx. She is a licensed, board-certified pediatrician with more than a decade of experience in academic medicine.

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