What can cause a hemifacial spasm in a 21 yr old? had a left eye twitch for 2 months and now corners of mouth left side are starting to twitch

Twitching: Subtle twitching of the muscles of facial expression is not exactly the same as hemifacial spasm. The spasm is a significant, long lasting contraction of the muscles, which is painful. Twitching can be caused by fatigue, nervousness, an infection, or sometimes a history of a condition like Bell's palsy. Sometimes twitching of these muscles is entirely benign.