The face is the only part of the body where the muscles are close to the skin. No other part of the body can express emotion through automatic or involuntary contractions like the facial expression muscles can. When the expression muscles contract, they can move the skin of the face, creating wrinkles and folds perpendicular to the muscle alignment. Botulinum toxin can block cholinergic nerve conduction and cause temporary paralysis and relaxation of skeletal muscles, and can be used to treat some muscle hyperfunction disorders, as well as to improve or eliminate wrinkles by temporarily weakening the hyperactive state of the expression muscles. All cholinergic nerve fibers have receptors for botulinum toxin, which is the basis for the action of botulinum toxin. Normally, when a nerve impulse is transmitted along the axon to the presynaptic membrane of the neuromuscular junction, pre-formed acetylcholine-containing vesicles separate from the presynaptic membrane and fuse with the axon membrane at the end of the axon, releasing their contents into the synaptic gap, where acetylcholine then acts on the muscle to cause it to contract. A group of proteins called the SNARE complex is responsible for the release of acetylcholine from the vesicles, and botulinum toxin blunts the SNARE complex. Over time, the axons reconnect to the muscle and eventually, motor endplate function is restored, so the effects of botulinum toxin are temporary. Plastic and cosmetic surgery applications of Botox are mainly used to paralyze and relax facial expression muscles. Facial muscles can be divided into two types: expression muscles and masticatory muscles. The travel and function of the expression muscles are relatively independent. While skeletal muscles throughout the body are usually connected to bone through ligaments that drive body movement, most facial expression muscles are not connected to bone, but to soft tissues that express emotional states by moving the skin and related structures. For example, raising and lowering the eyebrows can express surprise, anger, sadness, or fatigue. The expression muscles are connected to the skin by a series of fibers, which, together with the fascial layer between them, make up the SMAS system. When the deep facial expression muscles move, the skin attached to them moves with them. Facial masticatory muscles, such as the bite and temporalis muscles, have bony attachment points and function similarly to skeletal muscles in other parts of the body, which divide the movement of the jaw. Due to the reciprocal movement of facial expression muscles, the skin may develop wrinkles due to the repeated mechanical action. The wrinkles formed are perpendicular to the direction of muscle contraction, for example, the main muscle in the forehead is the frontalis muscle, and the frontalis fibers travel vertically, contracting to shorten the forehead and raise the eyebrows, resulting in horizontal horizontal wrinkles in the forehead. Some people overuse a muscle, keeping it in a constant state of hyperactivity, and after a long time permanent wrinkles can form in the direction perpendicular to the muscle movement, such as excessive contraction of the frown muscle can lead to vertical or oblique rows of wrinkles between the eyebrows. Botox can temporarily weaken the hyperactive state of facial muscles to improve or eliminate wrinkles.