Sodium tetradecyl sulfate (STS) is a commonly used synonym for 7-ethyl-2-methyl-4-undecanyl sulfate sodium salt which is anionicsurfactant that is the active component of the sclerosant drug Sotradecol. It is commonly used in the treatment of varicose and spider veins of the leg, during the procedure of sclerotherapy. Being a detergent, its action is on the lipid molecules in the cells of the vein wall, causing inflammatory destruction of the internal lining of the vein and thrombus formation eventually leading to sclerosis of the vein. It is used in concentrations ranging from 0.1% to 3% for this purpose. In the UK, Ireland, Italy, Australia, New Zealand and South Africa, it is sold under the trade-name Fibro-Vein in concentrations of 0.2%, 0.5%, 1.0%, and 3%.