Botox injection can slim the face, however, sometimes there will be a stiff facial expression after injection, what is the reason for this? 1, normal reaction: after the injection of botulinum toxin bite muscle muscle strength is weakened, there will be unnatural facial expressions, generally 2-8 weeks after the recovery of normal. 2, the position of botulinum toxin playing deviation: botulinum toxin should be injected accurately into two points, the first point is the most prominent part of the bite muscle, the second point is diagonally above the first point, 2, 5 cm from the first point. Any point position playing deviation, will cause facial expression stiffness, the duration will be greater than 8 weeks. 3.Injection position is too shallow: If Botox is injected into the upper layer of the bite muscle, it may damage the facial nerve and cause stiff facial expressions, and serious drooling and crooked corners of the mouth to one side will occur. 4, Botox injection is too much and the interval between injections is too short: when both sides of the bite muscle are injected with Botox, the total amount of each injection cannot be greater than 100 units; the interval between two injections cannot be less than 1 month, if these two criteria are exceeded, serious facial expression stiffness will occur. 5, massage the injection site after botulinum toxin injection: after botulinum toxin injection, if you massage with your hands, botulinum toxin will penetrate into the adjacent expression muscles, intensifying the occurrence of unnatural expressions. How to prevent facial stiffness after botulinum toxin injection? 1, Be sure to go to a regular hospital and find an experienced doctor for injection. 2.For six hours, do not wash your face, do not wear makeup, do not exercise, and do not massage the injection site. 3.For one week, abstain from spicy and seafood food, avoid smoking and alcohol, and avoid eating hard shell food.