Spider veins are dilated capillary veins <2mm that exist just below the skin surface. They may be blue, red or purple in color with a weblike or linear appearance.
Spider veins grow from reticular veins, also known as feeder veins. These feeders exist in a dense network, and are usually a bit deeper in the skin. Spider veins are proliferative in nature and often serve as a platform for the growth of additional veins if not treated. They are most commonly a cosmetic concern but can cause subtle symptoms such as aching, itching and throbbing. They can sometimes be a sign of underlying venous insufficiency.
Spider veins occur mainly in women. The most apparent cause of spider veins is hormones, among the other risk factors (age, obesity, genetics).
Men are also susceptible to small veins, but they are usually darker, larger, and are usually high pressure extensions from nearby varicose veins.