Facial nerve: the facial nerve's nuclei are in the brainstem (represented in the diagram by "θ"). Orange: nerves coming from the left hemisphere of the brain, yellow: nerves coming from the right hemisphere. Note that the forehead muscles receive innervation from both hemispheres (yellow and orange) The cause of<unk>  is unknown. Risk factors include diabetes, a recent upper respiratory tract infection, and pregnancy. Some viruses are thought to establish a persistent (or latent) infection without symptoms, e.g., the varicella zoster virus and the Epstein–Barr virus, both of the herpes family. Reactivation of an existing (dormant) viral infection has been suggested as a cause of acute<unk> . As the facial nerve swells and becomes inflamed in reaction to the infection, it causes pressure within the Fallopian canal, resulting in the restriction of blood and oxygen to the nerve cells. Other viruses and bacteria that have been linked to the development of<unk>  include HIV, sarcoidosis and Lyme Disease. This new activation could be triggered by trauma, environmental factors, and metabolic or emotional disorders. Familial inheritance has been found in 4–14% of cases. There may also be an association with migraines. In December 2020, the U.S. FDA recommended that recipients of the Pfizer and Moderna COVID-19 vaccines should be monitored for symptoms of<unk>  after several cases were reported among clinical trial participants, though the data were not sufficient to determine a causal link. Genetics A meta-analysis of genome-wide association study (GWAS) identified the first unequivocal association with<unk> .
Bell's palsy
Lyme disease
Erb's palsy
Stroke
Horner's syndrome
Ramsay Hunt syndrome type 2
Todd's paresis
Brain tumor