It's unclear exactly what causes Bell's palsy, but Dr. Zwerling says that it can be associated with a viral infection. "It's very common, especially in pregnant women compared to not pregnant women, or patients who are immunocompromised, like a diabetic patient," she says. "In some cases it can be associated with Lyme's disease." But the thing about Bell's palsy is that it's often confused with other more serious conditions that cause facial paralysis, like a stroke or brain tumor, she says. "In patients that have weakness on one side of their face, it doesn't mean that they have Bell's," she says. So before you can start a treatment plan, it's important to make sure the underlying cause is clear.