Editing Bell's palsy (section)

==Cause==
[[Image:Cranial nerve VII.svg|thumb|upright=1.3|[[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 Bell's palsy is unknown.<ref name=NIH2016/> Risk factors include [[diabetes]], a recent [[upper respiratory tract infection]], and [[pregnancy]].<ref name=NIH2016/><ref name=Preg2017/>

Some viruses are thought to establish a persistent (or [[virus latency|latent]]) infection without symptoms, e.g., the [[varicella zoster virus]]<ref>[http://www.medicinenet.com/facial_nerve_problems/page3.htm Facial Nerve Problems and Bell's Palsy Information on MedicineNet.com<!-- Bot generated title -->] ''www.medicinenet.com'' {{webarchive|url=https://web.archive.org/web/20080423075504/http://www.medicinenet.com/facial_nerve_problems/page3.htm |date=2008-04-23 }}</ref> and the [[Epstein–Barr virus]], both of the [[Herpesviridae#Human herpesvirus types|herpes family]]. Reactivation of an existing (dormant) viral infection has been suggested as a cause of acute Bell's palsy.<ref name=Furuta/> As the facial nerve swells and becomes inflamed in reaction to the infection, it causes pressure within the [[Facial canal|Fallopian canal]], resulting in the restriction of blood and oxygen to the nerve cells.<ref>{{Cite web |title=Bell's Palsy Fact Sheet {{!}} National Institute of Neurological Disorders and Stroke |url=https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Bells-Palsy-Fact-Sheet |access-date=2022-03-22 |website=www.ninds.nih.gov}}</ref> Other viral and bacterial infections that have been linked to the development of Bell's palsy include [[HIV]] and [[Lyme disease]].<ref>{{cite journal |vauthors=Lu H, Hu H |date=17 March 2023 |title=Bilateral facial palsy caused by HIV infection: A case report and literature review |journal=Medicine (Baltimore) |volume=102 |issue=11 |page=e33263 |doi=10.1097/MD.0000000000033263 |pmc=10019170 |pmid=36930128}}</ref><ref>{{cite journal |vauthors=McEntire CR, Chwalisz BK |date=1 May 2024 |title=Cranial nerve involvement, visual complications and headache syndromes in Lyme disease |journal=Curr Opin Ophthalmol |volume=35 |issue=3 |pages=265–271 |doi=10.1097/ICU.0000000000001031 |pmid=38518069}}</ref> This new activation could be triggered by trauma, environmental factors, and metabolic or emotional disorders.<ref name=Kasse>{{cite journal | vauthors = Kasse CA, Ferri RG, Vietler EY, Leonhardt FD, Testa JR, Cruz OL |title=Clinical data and prognosis in 1521 cases of Bell's palsy |journal=International Congress Series |volume=1240 |pages=641–47 |date=October 2003 |doi=10.1016/S0531-5131(03)00757-X }}</ref>

Familial inheritance has been found in 4–14% of cases.<ref name=Familial>{{cite journal | vauthors = Döner F, Kutluhan S | title = Familial idiopathic facial palsy | journal = European Archives of Oto-Rhino-Laryngology | volume = 257 | issue = 3 | pages = 117–19 | year = 2000 | pmid = 10839481 | doi = 10.1007/s004050050205 | url = http://link.springer.de/link/service/journals/00405/bibs/0257003/02570117.htm | url-status = dead | s2cid = 24403036 | archive-url = https://archive.today/20130106003939/http://link.springer.de/link/service/journals/00405/bibs/0257003/02570117.htm | archive-date = 2013-01-06 }}</ref> There may also be an association with [[migraines]].<ref>{{cite journal | vauthors = Silberstein SD, Silvestrini M | title = Does migraine produce facial palsy? For whom the Bell tolls | journal = Neurology | volume = 84 | issue = 2 | pages = 108–09 | date = January 2015 | pmid = 25520314 | doi = 10.1212/WNL.0000000000001136 | hdl = 11566/206361 | s2cid = 35589569 | hdl-access = free }}</ref>

In December 2020, the U.S. [[Food and Drug Administration|FDA]] recommended that recipients of the [[Pfizer–BioNTech COVID-19 vaccine|Pfizer]] and [[Moderna COVID-19 vaccine]]s should be monitored for symptoms of Bell's palsy after several cases were reported among clinical trial participants, though the data were not sufficient to determine a causal link.<ref>{{Cite web|last=Higgins-Dunn|first=Noah|date=2020-12-15|title=FDA staff recommends watching for Bell's palsy in Moderna and Pfizer vaccine recipients|url=https://www.cnbc.com/2020/12/15/fda-staff-recommends-watching-for-bells-palsy-in-moderna-and-pfizer-vaccine-recipients.html|access-date=2020-12-15|website=CNBC|language=en}}</ref>

===Genetics===
A meta-analysis of genome-wide association study (GWAS) identified the first unequivocal association with Bell's palsy.<ref>{{Cite journal|last=Skuladottir|first=Astros Th|date=2021-02-18|title=A meta-analysis uncovers the first sequence variant conferring risk of Bell's palsy|journal=Scientific Reports|volume=11|issue=1|page=4188|doi=10.1038/s41598-021-82736-w|pmid=33602968|pmc=7893061|bibcode=2021NatSR..11.4188S|language=en}}</ref>