Varicose veins and venous malformations are common and frequent diseases of the venous system in vascular surgery, with a high incidence and plagued by more severe clinical symptoms. Sclerotherapy has been used to treat varicose veins and venous malformations for more than 150 years. In 1853, Cassaigness first proposed sclerotherapy, in which a chemical sclerosing agent is injected into the varicose vein to cause a sterile inflammatory reaction secondary to the venous wall, and continuous postoperative compression causes the vein to atrophy, followed by fibrosis of the granulation tissue in the lumen of the atrophied vein, eventually forming a fibrous cord to treat The purpose of varicose veins and venous malformations. After liquid sclerotherapy is injected into the diseased vessel, it is rapidly diluted by blood and washed away by blood flow, making liquid sclerotherapy ineffective and requiring the use of large amounts of concentrated sclerotherapy to achieve the desired larger area of endothelial injury. Therefore, sclerotherapy has long been used only as an adjunct to surgical procedures. 1944 Orbach was the first to propose the therapeutic concept of foam sclerotherapy, which refers to a new foam-like sclerosing substance formed by mixing liquid sclerosing agents with gas. After continuous improvement and development in recent decades, foam sclerotherapy has become the most important treatment in the field of phlebology. After the foam sclerosing agent is injected into the diseased vessel, the blood equivalent to its own volume (gas + liquid sclerosing agent) can be expelled from the lumen of the vessel, and it is not easy to be diluted by blood and washed away by blood flow, so the contact area with the endothelium of the vessel is increased and the contact time is prolonged, which improves the efficacy but reduces the amount of sclerosing agent and thus reduces the adverse effects. At the same time, foam sclerosing agents can rapidly induce vasospasm, further enhancing the sclerosing efficacy. With the widespread use of foam sclerosing agents, the limitations of liquid sclerosing agents have been overcome to a large extent. The diseases in which foam sclerosing agents are used mainly include varicose veins of the lower extremities (Figure 1), capillary dilation, various superficial hemangiomas (Figure 2), vascular malformations, and postoperative recurrence of varicose veins. In principle, all types of varicose veins are suitable for sclerotherapy, and for smaller diameter varicose veins such as reticular row varicose veins and spider row varicose veins sclerotherapy is considered to be the preferred treatment option. Also, foam sclerotherapy has been proven to be an effective treatment for ovarian varicose veins, esophageal varicose veins, hemorrhoids, liver and kidney cysts, tendon sheath cysts, etc. The treatment is basically painless and has long lasting effects. The aim of sclerotherapy is mainly to treat varicose veins and prevent possible complications, reduce or eliminate existing symptoms, improve pathological hemodynamic conditions, and achieve good results to meet cosmetic and functional requirements. Foam sclerotherapy has become one of the most important developments in the field of phlebology in the last decade due to its efficiency, speed, safety, affordability and reproducibility, and it is widely believed that it will dominate the treatment of varicose veins and venous malformations. Figure 1 Before and after sclerotherapy of varicose veins in the lower extremities Figure 2 Before and after treatment of hemangioma