Numbness on one side of the face can be caused by acoustic neuroma, diabetes mellitus, Bell's palsy, strokes, peripheral nerve trauma or trigeminal neuralgia, according to Right Diagnosis. Generally speaking, numbness is caused by damage, irritation or compression of the nerves that are in the facial region. Depending on whether only a single branch of nerves or several nerves are affected, the surface area that feels numb will vary.
The reason why these conditions cause a numbing sensation to one side of the face will vary. For example, acoustic neuroma is a benign tumor that is present on the main nerve that leads from the inner ear to the brain, and is not entirely that common. Depending on the growth of the tumor and which tissues and nerves that it presses against, patients will experience different types of numbing sensations to various regions of their face.
Although individuals who are experiencing numbness on one side of their face should seek medical attention, it is not generally considered an emergency, but merely an indication that something is wrong. It is considered an emergency if the numbness is accompanied with other symptoms, such as confusion, difficulty talking, paralysis or weakness, dizziness or sudden and severe headaches.