(See also Overview of the Venous System.)
Many people with or without varicose veins may have spider veins, which are enlarged capillaries. Capillaries are tiny, extremely thin-walled vessels that act as a bridge between arteries (which carry blood away from the heart) and veins (which carry blood back to the heart).
Spider veins may be caused by the pressure from blood in varicose veins, but the cause is generally thought to be hormonal factors that are not yet understood. A hormonal cause would explain why spider veins most commonly occur in women, particularly during pregnancy.
Spider veins usually cause no symptoms. Some people do have pain or burning. Many people consider spider veins unsightly. Doctors recognize spider veins by their appearance. Tests are not needed.
Spider veins can usually be eliminated by injection therapy (sclerotherapy) similar to that done for varicose veins. In sclerotherapy, a solution, such as sodium tetradecyl sulfate, is injected into each of the spider veins to irritate them and produce a blood clot that blocks them. Large areas of spider veins (multiple telangiectasias) may require several treatments because the injections are painful. The skin may darken, but this discoloration usually subsides, often completely.
Laser treatment is also effective, but large areas require several treatments. This therapy uses a laser beam to destroy the small veins.
Small spider veins may persist or recur after initial treatment.