Both of these protective sheaths can be altered during a Bell s palsy episode. The trigger of Bell s palsy attacks is not known either. For most people, the symptoms develop with alarming speed. Some patients have reported that before an attack, they had been exposed to a draft, an air-conditioning outlet or an open window. Taxi drivers who develop Bell s palsy tend to get it on the left sides of their faces, the side usually exposed to the open window.
Many studies strongly suggest the activation of a virus.
Viruses in the herpes family have a predilection for nerve tissue and have been suspected for many years as a possible cause. More than 20 years ago, researchers proposed an etiologic link between herpes simplex virus, or HSV, and Bell s palsy. Using molecular technology notably the polymerase chain reaction test these studies demonstrated active HSV in tissues from patients with recent onset of Bell s palsy. In another study, a causal relationship between HSV and Bell s palsy in a majority of the patients was demonstrated. The authors suggested changing the disease s name from Bell s palsy to herpetic facial paralysis.