Bell’s palsy is believed to be caused by inflammation of the facial nerve (Mayo Clinic 2012a). The facial nerve controls many of the muscles involved in facial expressions and also carries sensory information from the anterior (frontal) two-thirds of the tongue (Misulis 2010). In addition, this nerve also helps control the lacrimal glands (responsible for tear production) and submandibular glands (involved in producing saliva) (Kosins 2007; Zandian 2014; Ronthal 2013a).
The facial nerve passes through small canals in the skull along its path to innervate the facial muscles. When a dormant virus reactivates and migrates into the facial nerve, an inflammatory response ensues, leading to swelling and compression of the nerve within these small bony passages. Non-infectious factors, such as autoimmune processes, may also cause inflammation of the facial nerve and contribute to Bell’s palsy (Zandian 2014; Ogawa 1982; Sekiya 1990; Gantz 1983; Kölln 2011).
Most people with Bell’s palsy recover considerably well without treatment within 2 to 3 weeks, achieving full recovery within 3 or 4 months. About 70% of the patients with complete paralysis and up to 94% of the patients with partial paralysis completely recover their facial muscle function, even without treatment. On rare occasions, long-term problems such as facial weakness or involuntary facial movements may arise. Overall, 80-90% of patients have complete recovery within 6 weeks to 3 months. Nevertheless, Bell’s palsy may produce psychologically troubling symptoms such as drooling and abnormal facial appearance; some patients also report changes in hearing in the ear on the affected side, dizziness, abnormal taste sensation, pain or discomfort around the jaw, and difficulty eating or drinking (Taylor 2013; Holland 2004; Baugh 2013; Kölln 2009; Mooney 2013; Zandian 2014; NINDS 2012).
One important consideration is that inability to close the eye on the affected side of the face can cause the cornea to become dried out (A.D.A.M. 2013), which could lead to long-term visual impairment. Thus, it is important to seek proper medical care from a qualified healthcare provider to ensure appropriate precautions are taken. Consulting a physician as soon as symptoms emerge is also important because delayed diagnosis and treatment may increase the likelihood of long-term problems (Taylor 2013; Holland 2004; Baugh 2013; Kölln 2009; Mooney 2013; Ronthal 2013b).