Bell’s palsy is a disease condition which happens due to involvement of the 7th cranial nerve i.e. the facial nerve. This particular nerve is useful in our facial expression (including closing the eyelids and smiling) and also to perceive taste at the anterior 2/3rd of our tongue.
Facial nerve involvement causes weakness of facial muscles. Therefore the person affected with the problem is unable to smile (due to weakness of muscles responsible for smile) or blow a whistle properly (due to weakness of check muscles) or can’t shut there eyes properly as the eye lid closing muscles are also supplied by the facial nerve).
Sometimes saliva might drool from the affects side of the face and food might accumulate the corners of mouth between the jaw and cheeks, all attribute to weakness of facial muscles. In addition to that the taste sensation of anterior 2/3rd of the tongue might be distorted or lost. As the facial nerve supplies a ear muscle called stapedius, normal sound may be perceived louder, a phenomenon called hyperacusis.
Generally the condition is of sudden onset and no other cause of facial weakness is not detectable.