Doctors usually can diagnose Bell's palsy based on a physical examination. Your doctor will test for weakness in the muscles of the face, paying special attention to your ability to close both eyes and hold them closed. He or she also will ask you to smile or whistle to look for a difference on the two sides of your face. Your doctor will ask whether you are having any symptoms of numbness or weakness in other body parts or difficulty walking. These symptoms are not associated with Bell's palsy, but this will help to rule out other causes of facial weakness.
Your doctor will look for a shingles like rash on your face and ear. If you have this rash, especially if it is painful, your doctor will diagnose Ramsay-Hunt syndrome caused by reactivation of the herpes zoster virus.
If there are no other symptoms, and the only problem is weakness in facial muscles, your doctor can diagnose Bell's palsy without further testing. A blood sugar test may be ordered if you have not had one recently, because people with diabetes are more likely to get Bell's palsy. A blood test for Lyme disease also may be done.