There are several reasons for involuntary twitching of lower lip muscles: 1st, due to excitement and mental tension, when people are excited and tense, due to disorder of plant nerves, resulting in abnormal excitement of sympathetic nerves, many muscles will appear involuntary twitching phenomenon, especially when nervous and excited, if you want to talk or express something, the lower lip muscle twitching phenomenon will appear. No. 2, lower lip muscle twitching may also be caused by cerebrovascular accidents and other diseases, many cerebrovascular accidents will appear after the abnormal situation of facial muscles, appearing lower lip muscle twitching, mouth and eyes askew, drooling symptoms. No. 3, lower lip muscle twitching may also be caused by facial neuritis, generally due to various causes of facial neuritis will appear lower lip muscle involuntary twitching, will also appear facial palsy, mouth and eyes crooked symptoms.