The so-called expression, is an important symbol of the evolution of higher animals, kittens and puppies can also express anger and fear, that is the simplest, when it comes to human beings is complicated. A human face is divided into two parts, and people have seen two faces with one big and one small, but have they ever seen an asymmetrical smile? Facial paralysis is the most common, but it is not within the scope of our discussion because it is too obvious. Besides facial paralysis, asymmetry of both sides of the smile should be a rare case, having seen 4-5 cases over the years. I categorize him into 3 causes: First, it is congenital, this should be the most classic. I have seen 3 cases where the height of the two corners of the mouth and the upper lip were asymmetrical when smiling, and it was more obvious, so I felt more annoyed and asked for a solution. The presentation was that the height of the corners of the mouth and upper lip on the affected side was significantly higher than on the opposite side, and the nasolabial folds deepened. Why don’t we say that it is the healthy side that is low in strength? Because we have the normal human level of evaluation. In another case, when opening the mouth, the two lower lips were asymmetrical and obvious, the picture below illustrates the problem, and this person was very satisfied after a short outpatient surgery. Secondly, traumatic ones are common. It is related to the uneven strength of the muscles, some can recover on their own, some can’t, and those who haven’t fully recovered after 1-2 years may need surgery to solve the problem. Thirdly, medical, we have seen the asymmetry of lower lip movement caused by chin surgery, which is easier to correct.