Normal veins carry venous blood back to the heart. Inside these veins, one-way valves ensure that blood only travels toward the heart and help equalize the blood pressure along the vein. Faulty veins can lead to a condition of venous insufficiency, which can result in the appearance of enlarged small surface veins (venules) called spider veins.
Typically, spider veins appear to have a diameter of 1 millimeter or less, although their actual diameter may be up to 3 mm under the surface. Small varicose veins are usually pinkish red, whereas larger vessels are blue or purple in color.
Sometimes a cluster of spider veins may appear as a red or purple patch called blushing or matting (telangiectatic matting) , that are often mistaken for bruises. Unlike bruises, however, spider vein mattings do not fade. Another form of spider veins, called an ankle flare is a cluster of spider veins, usually associated with varicose veins, that is located on the inner ankle.
Most spider veins are not symptomatic and are usually only considered a cosmetic problem. Some cases of spider veins - especially those of that develop from deeper "reticular" or feeder veins, however, come with a burning sensation or a dull, throbbing pain.