The surgical treatment of hyperhidrosis, which has a significant negative impact on the quality of life of patients and impairs their social and work abilities, is primarily thoracoscopic sympathectomy. Sympathetic nerve chain dissection is the destruction of part of the sympathetic nerve trunk for the treatment of hyperhidrosis, including hand or axillary hyperhidrosis, head and facial sweating, facial flushing, and social phobia. 1. Sympathetic nerve chain physiology: The sympathetic nerve chain is a bundle of paired nerves divided into cervical, thoracic and lumbar parts, which are autonomic nerves that innervate the autonomic functions of the limbs, such as respiration, sweating and blood pressure regulation. The most commonly involved site after the off-end sympathetic nerve is in the upper thorax, and this part of the sympathetic chain is between the bottom 1-5 thoracic vertebrae. (1) The first sympathetic ganglion (T1) mainly innervates facial and hand sweating and heat dissipation, and part of T1 merges with the inferior cervical nerve to form a stellate ganglion, which mainly innervates the pupillary reflex and eyelid, and if this part of the ganglion is injured, Horner’s sign (pupil narrowing, eye entropion, ptosis and absence of sweating on the affected side) may occur. (2) The second sympathetic ganglion (T2) innervates the sweat glands of the face, scalp, shoulders, chest above the breasts and hands, and facial flushing. (3) T3 innervates sweating in parts of the face, hands, axillae, shoulders, and chest above the breasts. (4) T4 is located in the hands and axillae. It is important to note the multiple innervation of the sympathetic nerves to the face, hands and axillae. Treatment of palmar hyperhidrosis: Excessive sweating on the palms and soles of the feet is bound to greatly affect one’s quality of life and work. Classical sympathectomy involves mainly damaged destruction of T2 and/or T3 ganglia, and electrocautery and/or clamping of these sites can achieve a high satisfaction rate, with complications including mainly: recurrence of hyperhidrosis, gustatory sweating syndrome and compensatory sweating, occasionally Horner’s sign (Horner), neuralgia or pneumothorax. Of all sympathectomy-related complications, compensatory sweating is the most common cause of patient dissatisfaction. There has been much debate about the appropriate site for sympathectomy, with T2 or T2-3 initially recommended as the appropriate site for sympathectomy for palmar hyperhidrosis. However, increasingly sympathectomy at the low orthognathic surface is less likely to result in compensatory sweating and can be more satisfying for patients with palmar hyperhidrosis. More scholars are now recommending T3 or T4 sympathetic chain dissection for palmar hyperhidrosis, where T4 is less likely to result in not only no sweating but also less likely to result in compensatory sweating. The physiological rationale for the choice of T4 level sympathetic neurotomy is mainly related to the negative feedback mechanism of the autonomic nerves. In the neurological reflex, the hypothalamus is first stimulated and signals are transmitted through the autonomic nervous system to the sweat glands, which then secrete sweat and send negative feedback signals through the sympathetic trunk to the hypothalamus, interrupting the signal from the hypothalamus. If the T2 level is cut, the negative feedback signal cannot reach the hypothalamus, resulting in a dominance of the uninterrupted positive signal from the hypothalamus to the sweat glands, which leads to more severe compensatory sweating. If T4 is cut, the negative signals from T2 and T3 are retained, producing a negative signal in the hypothalamus, which leads to a lower intensity of positive signals reaching the sweat glands, resulting in a milder degree of compensatory sweating. 3. Craniofacial hyperhidrosis: There is less evidence for the effectiveness of sympathetic chain dissection for craniofacial hyperhidrosis, and patients have a higher rate of postoperative dissatisfaction compared to palmar and axillary hyperhidrosis. Sympathetic nerve chain dissection for craniofacial hyperhidrosis is mainly chosen at the T2 level, where the T2 and T1 ganglia are close to each other and are associated, predisposing to complications such as compensatory sweating and Horner’s sign. For craniofacial hyperhidrosis, clamping instead of cutting the sympathetic chain because of its reversibility may be a better solution. Sympathetic chain dissection at the T4 and T5 levels is mostly recommended for axillary hyperhidrosis, but has a significant failure rate. Alternatively, removal of the axillary sweat glands is an option, but is relatively more invasive and sympathetic chain dissection can usually be attempted first. Finally, T3 or T4 sympathectomy is still highly recommended for palmar hyperhidrosis, T2 sympathetic chain clamping is an option for head and facial hyperhidrosis, and T4 or T5 sympathetic chain dissection can be attempted for axillary hyperhidrosis.