Named after the spidery, twig-like clusters that form just beneath the skin, spider veins can appear dark blue, red or purple. Often seen in these unsightly clusters, they may sometimes also appear as a single vein or a dark bluish vein. This, however, is less common.
The causes are multiple, from venous reflux to heredity to pregnancy, hormonal changes, or leg trauma. While extremely unsightly, they are not commonly associated with larger medical issues and are normally treated with injection sclerotherapy or compression hose.