The aim of this study was to explore the risk factors for Bell's palsy (BP) and to examine whether psychological factors are the potential risk factors for the occurrence of BP.

We conducted a case-control, multi-center clinical investigation. A total of 695 subjects were assigned to the case group (n=355) and the control group (n=340). All the BP patients were enrolled from 11 State Hospitals in China, and all the controls were selected from the same district to match for the patients. The study was coordinated by a tertiary referral centre, Tongji Hospital. The House-Brackmann grading system and Facial Disability Index (FDI) was adopted to assess the BP patients. Kessler 10-Item Psychological Distress Scale（K10）was usde to explore the psychological distress, and the Cattell 16 Personality Factor (16PF) scale was employed to evaluate the personality profiles of all subjects.

Inclusion criteria:

1. Patients who were diagnosed to have unilateral facial-nerve weakness without any identifiable causes within 168 hours after onset of symptoms;
2. aged 18 to 65 years.

Exclusion criteria：

1. illiterate;
2. the facial paralysis is caused by herpes zoster;
3. recurrent facial paralysis;
4. noticeable asymmetry of the face before the illness which may affect the evaluation;
5. history of peptic ulcer disease, severe hypertension, uncontrolled diabetes, liver and kidney dysfunction, pregnancy, mental illness, or serious systemic diseases which may affect the treatment.

695 subjects were assigned to Cases Group (n=355) and Control Group (n=340).