Bell's palsy is a type of temporary paralysis of the facial muscles, according to the National Institutes of Neurological Disorders and Stroke. It occurs due to damage to the seventh cranial nerve, more commonly called the facial nerve.
Bell's palsy is the most common type of facial paralysis, reports the NINDS. The facial nerve is responsible for controlling the muscles responsible for facial expressions, blinking and other functions. When something happens to disrupt its ability to transmit instructions, the result is facial weakness or paralysis. This paralysis usually just affects the nerve on one side of the face, although in rare cases, both sides are affected.
People sometimes mistake Bell's palsy for a stroke, but there is no relationship between the two diseases. The most common cause of Bell's palsy is inflammation that puts too much pressure on the facial nerve, according to WebMD. Even minor inflammation can disrupt the nerve's ability to function, because it passes through a narrow channel of bone.
The exact reason it occurs is often unclear, although it may be linked to the herpes virus. Other common viral infections are also possible causes, including flu, measles, mumps and chickenpox, as reported by the Mayo Clinic. The NINDS also lists physical trauma as a possible cause. Bell's palsy is often diagnosed when no other cause for facial paralysis can be determined, claims WebMD.