Sclerotherapy is the injection of liquid or foam sclerosing agents into abnormally dilated or aesthetically disturbed veins, causing endothelial damage through the reaction of the sclerosing agent with the endothelium, resulting in closure and sclerosis of the target vessel, which is eventually absorbed by the surrounding tissue. Sclerotherapy is a minimally invasive treatment for chronic venous disease of the lower extremities and is currently used for capillary dilation, reticular venous dilation, varicose veins, and some venous malformations. Sclerotherapy is a long-tested and safe treatment both for aesthetic and therapeutic purposes. By selecting the right patient, sclerotherapy is sure to provide satisfactory results. There are two main sclerotherapy agents, the most used is polydocanol, and the other is sodium tetradecyl sulfate. Both of them have a molecular structure in the form of long-chain fatty acids and are amphiphilic, so that they form particles with a bilayer structure. These particles interact with the cell membrane of endothelial cells causing denaturation of the proteins on the cell membrane and destruction of the endothelial cells, thus causing vascular fibrosis. These sclerosing agents can be injected both as a liquid and, due to their molecular properties, can also be used in foam form. Depending on the diameter of the vessel targeted for treatment, the appropriate liquid or foam sclerosing agent should be used. In general, liquid sclerotherapy is recommended for capillary dilation, while foam sclerotherapy is more effective than liquid sclerotherapy for reticular dilation, saphenous varicose veins, small saphenous varicose veins and some venous malformations. The main indications for sclerotherapy are capillary dilation, reticular venous dilation, saphenous varicose veins, small saphenous varicose veins, varicose veins with insufficiency of penetrating veins, residual or recurrent varicose veins after treatment, venous ulcers and venous malformations. Absolute contraindications to sclerotherapy include: allergy to sclerosing agents; severe systemic disease in which the patient cannot tolerate sclerotherapy; acute superficial venous thrombosis or deep venous thrombosis; local infection in the treated area; severe systemic infection; patient requiring braking or prolonged bed rest; severe arterial occlusive disease; and symptomatic patent foramen ovale is also a contraindication for patients treated with foam sclerotherapy. Although symptomatic patent foramen ovale is a contraindication, cardiac ultrasound to rule out patent foramen ovale is not recommended for all patients injected with foam sclerotherapy. Relative contraindications include: pregnancy; lower extremity edema; poor glycemic control in patients with diabetes; advanced complications of diabetes; moderate arterial occlusive disease; poor general condition of the patient; bronchial asthma; and significant allergies. In addition, for patients requiring sclerotherapy, the presence of a hypercoagulable state, coagulation disorders, and a history of deep vein thrombosis need to be considered, and although these are not contraindications, they need to be weighed by the treating patient. Clinical results The results of sclerotherapy in the treatment of capillary and reticular venous dilatation are relatively satisfactory, and postoperative recurrence is uncommon; most cases of recurrence are due to inadequate treatment. In the treatment of varicose veins foam sclerotherapy can significantly relieve patients’ symptoms and improve their quality of life. However, the results of randomized controlled studies have shown that foam sclerotherapy has a slightly higher rate of postoperative varicose vein recurrence than conventional surgery. A prospective study by Chapman et al. showed that the recanalization rate was 27% at 1 year and up to 64% at 5 years after foam sclerotherapy, and 16,5% of patients may need to be re-treated with foam sclerotherapy within 2 years after surgery. For ulcers caused by varicose veins, the efficacy of foam sclerotherapy is also satisfactory, with ulcer healing rates reported in the literature ranging from 79% to 96%. The advantages of sclerotherapy over surgical treatment are less invasive, faster postoperative recovery, and less pain for the patient. In addition sclerotherapy is relatively less expensive than other minimally invasive treatments for varicose veins, such as laser and radiofrequency. Complications Although the safety of sclerotherapy for lower extremity venous disease has been confirmed by numerous studies, the complications associated with sclerotherapy cannot be ignored. Some complications can affect the aesthetics of the affected limb, such as local capillary dilation and hyperpigmentation, while others can affect the quality of life of patients and even endanger their lives, such as skin necrosis, stroke, and deep vein thrombosis. Next, we will discuss the complications associated with sclerotherapy and related preventive treatment methods. 1, local capillary dilation may occur due to sclerotherapy causing outflow vessel obstruction, endothelial destruction and changes in the hormonal environment of surrounding tissues, resulting in local small vessel proliferation. Sclerotherapy injections for capillary dilation and reticular dilation should be carefully examined to adequately address venous reflux that may lead to capillary dilation or reticular dilation. Other preventive measures include 1) choosing the appropriate sclerosing agent concentration for the different vessel diameters and minimizing the concentration of sclerosing agent used. 2) reducing the amount of injection at each site. 3) appropriate compression after treatment. For local capillary dilatation where reflux may exist, sclerosing agents can be applied again to treat these venous refluxes. 2. The incidence of hyperpigmentation reported in the literature is not the same, ranging from 6% to 80%, due to the type and concentration of sclerosing agent used. The causes of hyperpigmentation may be serum heme deposition and post-inflammatory hyperpigmentation. Hyperpigmentation due to sclerotherapy tends to be self-healing, with the vast majority disappearing after 1 year, or if not self-healing, laser treatment can be used. 3, skin necrosis occurs very rarely. The main reason for skin necrosis is that the sclerosing agent is mistakenly injected into the small artery, causing continuous spasm of the artery and ischemia of the distal tissue causing skin necrosis. In addition, local arterial embolism causes distal tissue ischemia, and there may be complications such as fascial compartment syndrome, tissue necrosis, and nerve injury. In general, skin necrosis <4 mm in diameter can heal with diligent dressing changes, but small scars may remain, and in rare cases, the necrotic focus needs to be excised and re-sutured. To reduce the risk of accidental injection of small arteries, the injected vessel should be carefully observed during treatment to distinguish between arteries or veins. Other treatment measures include local infiltrative injection of 1% lidocaine, cold compresses, systemic heparinization, intravenous application of dextran, oral vasodilators, and thrombolytic therapy. In addition, in bony areas with less soft tissue, such as the ankle, postoperative compression therapy should avoid excessive pressure to prevent local skin necrosis. 4, the incidence of superficial venous thrombosis is not high, some literature reports the incidence of superficial venous thrombosis is 4, 4%, in the clinical sclerosis of veins after sclerotherapy and superficial venous thrombosis and thrombophlebitis are often not easy to distinguish, and the diagnosis of superficial venous thrombosis often depends on the symptoms associated with thrombophlebitis, such as hard erythema with pressure pain, so superficial venous thrombosis without symptoms may be missed. Superficial venous thrombosis tends to heal spontaneously, and treatment includes continuous compression with compression stockings, elevation of the affected limb, and the use of nonsteroidal anti-inflammatory drugs. Anticoagulation is not a routine treatment. 5. The incidence of deep vein thrombosis after foam sclerotherapy varies across the literature, probably because some asymptomatic patients with deep vein thrombosis are not detected in time. In a French registry study that included 12,173 cases, only 1 presented with thrombosis in the proximal deep vein and 5 with deep vein thrombosis at the calf. A UK study that included 11537 cases showed a 0,5% incidence of deep vein thrombosis. In contrast, the incidence of deep vein thrombosis in the study by Myer et al. was as high as 3,2%, but none of these patients had corresponding symptoms. Therefore, some patients with deep vein thrombosis after clinical foam sclerotherapy may be at risk of missing the diagnosis, but whether this has an impact on patient prognosis needs further study. Hypercoagulable states, excessive injection doses, and concurrent surgical treatment all increase the risk of DVT. Applying compression gradient stockings after sclerotherapy and encouraging early patient activity may reduce the risk of deep vein thrombosis. 6, the incidence of sclerotherapy allergy is not high, some literature reports the incidence is only 0, 6%. Patients with allergies should be cautioned in the selection of patients, and once an allergic manifestation occurs during sclerotherapy injection, the injection should be stopped immediately and appropriate supportive therapy should be taken. 7. Neurological complications include visual disturbance, migraine, transient ischemic attack and stroke. The incidence of visual disturbance after foam sclerotherapy is 1,4%. One is the presence of right-to-left shunt, especially the foramen ovale is not closed, so that part of the gas in the foam sclerosing agent can enter the body circulation through these shunt pathways, especially into the carotid system may cause the corresponding symptoms; the other sclerosing agent and vascular reaction caused by 5-hydroxytryptamine and endothelin-1 elevation, resulting in part of the vascular The other sclerosing agent reacts with the blood vessels causing an increase in 5-hydroxytryptamine and endothelin-1, leading to partial vasoconstriction and migraine and visual disturbances. The incidence of both transient ischemic attacks and strokes is very low, with a 0.01% incidence of stroke reported in the literature. The incidence of transient ischemic attacks and strokes is mainly related to the right-to-left shunt pathway, where gas or thrombus emboli caused by sclerosing agents enter the intracranial arterial system through the shunt and cause the corresponding symptoms. Therefore, the dosage of sclerosing agents should be severely controlled, the patient's lower limbs should be elevated during the injection, and the patient should lie still for 5-10 minutes after the injection and avoid Valsalva maneuvers. Overall, sclerotherapy is safe and effective in the treatment of lower extremity venous disease and can meet the requirements of some patients for minimally invasive, aesthetic and other aspects. As long as the indications and contraindications are strictly controlled, the treatment is performed according to standard operating procedures and certain precautions are taken, most complications should be avoided.