Prominent or visible leg veins are very common and may be unsightly. Their exact cause is unknown, although genetics, childbearing, and long periods  of standing are thought to play a role in their formation. Most spider veins are treated with sclerotherapy, although some may be treated with a laser. 

Sclerotherapy involves the injection of a sclerosing solution into small vessels, causing the vessels to close and slowly fade away. The veins start to fade within one week, continuing over a period of four to six weeks. 

A laser may be used to treat some of the smaller veins on the legs. This may result in darkening around the treated vein similar to a bruise, which may last for several months. 

More than one treatment is usually necessary for optimal effects. Most patients can expect a 50 to  80 percent improvement with a series of treatments.