Thread veins, or spider veins, are small, thin veins that appear beneath the surface of the skin. Thread veins are different from varicose veins, which are generally found on the legs, and are usually larger and darker in color, and protrude more from the surface of the skin. Thread veins are often blue or red in color and do not generally protrude at all from the skin. They may appear on the legs as well as the face. Thread veins can cover a large or small area of the skin and often take on a jagged appearance, like that of a tree branch, and they are usually no more than 0.08 inches (2 mm) long.
Spider veins typically occur when the circulatory system does not function properly. Sometimes blood does not flow back from the extremities to the heart as efficiently as it should. This can lead to the enlargement of small blood vessels, or capillaries, causing spider veins to appear. Spider veins are similar to varicose veins, but are typically considered far less cause for concern.
Other causes of spider veins can include excessive standing — such as that done by those who stand on the job — pregnancy, obesity, menopause or puberty, and heredity. Thread veins can occur as a result of excessive exposure to UV rays, the use of some topical medications, such as steroid creams, or even as a result of the aging process.
Thread veins are not typically considered a medical problem in need of treatment. Complications can occur as a result of spider veins, though they are typically limited to mild pain in the legs. If the spider veins become inflamed and sore, or if rashes or ulcers appear on the area, medical treatment may be needed.
Many choose to treat thread veins for cosmetic reasons. Thread veins can be treated using laser therapy, which is considered very effective for reducing the appearance of spider veins on the face. Laser therapy may require several sessions and may not be right for those with darker complexions.
Micro-sclerotherapy is a common treatment for thread veins, mostly those found on the legs. In micro-sclerotherapy, a coagulating agent is typically injected directly into the affected capillaries. Micro-sclerotherapy is generally most effective after multiple sessions. It often requires the use of a compression bandage after treatment.