Facial or Bell's palsy is a condition that causes sudden weakness in the muscles on one side of the face. In most cases, the weakness is temporary and significantly improves over weeks. The weakness makes half of the face appear to droop. Smiles are one-sided, and the eye on the affected side resists closing.
Various viruses may trigger Bell’s palsy. The condition occurs when swelling or inflammation temporarily puts pressure on the nerve that controls facial muscles. This pressure impairs the function of the nerve making it difficult for you to control facial muscles or expressions. As the inflammation subsides, the nerve starts to function again. It may take several months for symptoms to go away.