5 common reasons for sudden facial asymmetry

Facial asymmetry refers to one-sided physical or aesthetic differences between the left and right side of the face. If it appears on both sides, it will be symmetric. Acute onset facial asymmetry usually refers to an injury or an impingement to the facial nerve, which is the nerve that is responsible for most of the functions in the face, causing facial weakness or paralysis over a relatively short amount of time.Although such an injury could occur as a result facial/head injury caused by external trauma, the main focus will be on those causes that are related to the muscles and nerves of the face.  

Bell’s Palsy

Bell’s palsy is the leading cause of facial asymmetry the United States with up to 40,000 cases per year and is responsible for 72% of facial paralysis. It is typically characterized by weakness to one side of the face and although causes of Bell’s palsy are typically unknown, there is growing evidence that most cases likely involve the reactivation of herpes simplex virus.


Strokes can present as one-sided facial droop and is a probable cause for facial asymmetry over a relatively short time. The clinical presentation of this is quite similar to the bell’s palsy and it could be misdiagnosed as bell’s palsy due to their striking resemblance.

Lyme disease

Lyme disease is commonly caused by bites from deer ticks which are commonly found in north-eastern and north-central regions of the United States. Facial nerve injury is a common symptom of Lyme disease occurring in about 50% of American cases. Facial paralysis caused by Lyme could be asymmetric or symmetric.


Sarcoidosis is an autoimmune disease that can affect all your organs, for example, brain, liver, lungs and kidney. Sarcoidosis patients who develop neurological symptoms are said to have neurosarcoidosis, and facial nerve injuries which cause facial weakness are a common symptom. In the case of neurosarcoidosis, facial abnormalities can be symmetric or asymmetric.


Intracranial tumors can physically push against the facial nerve which can cause one-sided facial weakness leading to facial asymmetry. Facial nerve injuries caused by tumors usually progress slowly overtime but acute onset facial weakness is also possible.

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