What Is Sclerotherapy? Sclerotherapy is a minimally invasive medical procedure designed to treat vascular conditions such as spider veins (telangiectasias) and small varicose veins. It involves injecting a sclerosing agent—commonly polidocanol (available in 0.5% or 1.0% liquid or as microfoam)—directly into target veins, causing them to collapse and gradually fade as the body absorbs them.