It is a weakness or paralysis of the muscles of one side of the face. The face droops on that side and there is inability to close the eye on the affected side. The problem is with the nerve that controls the muscles on that side of the face, rather than due to any pressure. The exact cause of Bell's palsy is not known. It is believed to be caused due to a viral infection of the facial nerve. This infection causes the nerve to swell and press against the bony canal through which it passes into the face. This leads to a failure in the transmission of signals to the facial muscles thus causing paralysis. It usually starts with an ache behind one of the ears followed by weakness or paralysis in the facial muscles on the same side. The paralysis or weakness generally starts in the lower face. There may be a decrease in taste, a change in hearing, tears in the eye and the inability to whistle or hold food in the mouth. The severity can vary from a mild weakness to complete paralysis. The severity of the illness is directly proportional to the speed of progression of the symptoms. The development of symptoms can take as little as a few hours (sometimes overnight) to a couple of days. The doctor will review the symptoms and conduct an examination. Other causes of facial paralysis have to be excluded. The causes of facial paralysis other than Bell's palsy include an injury to the nerve (skull fracture), stroke, acute or chronic ear infection, tumour in the ear or in the parotid (salivary gland in front of the ear), and a viral illness such as shingles. An ear, nose, throat, and a neurological exam will exclude most of the other causes of facial paralysis. A hearing test is done to check for an inner ear tumour. A CT scan of the head may be done to rule out a tumour in the ear or brain. Electrical testing on the nerve may be required to know the extent of damage.