Bell's palsy is primarily caused by swelling and inflammation of the facial nerve (cranial nerve VII), which controls the muscles on one side of the face. This swelling compresses the nerve as it passes through a narrow bony canal in the skull, disrupting nerve function and leading to temporary facial paralysis
. The exact reason for this nerve swelling is not fully understood, but it is often linked to viral infections. The herpes simplex virus type 1 (HSV-1), which causes cold sores, is the most commonly implicated virus. Other viruses that may trigger Bell's palsy include varicella (chickenpox), coxsackievirus, cytomegalovirus, mumps, rubella, mononucleosis, influenza, and possibly COVID-19 or vaccines for these viruses
. Additional factors that may contribute or increase the risk include:
- Diabetes, high blood pressure, obesity, and pregnancy (especially preeclampsia)
- Weakened immune system due to stress, sleep deprivation, minor illness, or autoimmune disorders
- Other infections such as Lyme disease, which can cause similar facial nerve inflammation but is distinct from Bell's palsy
In summary, Bell's palsy is thought to result from inflammation and swelling of the facial nerve often triggered by viral infections or immune-related factors, causing temporary facial muscle weakness or paralysis
