Botox works by weakening muscles that cause movement. If the muscles do not move as intensely, the lines formed by these muscle contractions will smooth out over time (about a month after your treatment). One of the risks of treating the lower face is that those muscles are needed for everyday activities such as talking, smiling, kissing, and chewing. If the incorrect muscle is treated, there is diffusion of the product into surrounding muscles, or too much is used, weakness can happen. Fortunately, it will fade and you will have no permanent problems. Most patients that experience this side effect will notice an improvement in about 2 weeks with complete resolution by 3 months. To minimize your risk of this happening, it is best to be treated by a Board Certified Dermatologist experienced in this treatment with excellent knowledge of facial anatomy.