A number of factors contribute to the development of spider veins, including heredity, pregnancy and other events that cause hormonal shifts, weight gain, occupations or activities that require prolonged sitting or standing, and the use of certain medications.
Spider veins usually take on one of three basic patterns. They may appear in a true spider shape with a group of veins radiating outward from a dark central point; they may be arborizing and will resemble tiny branch-like shapes; or they may be linear and appear as thin separate lines. Linear spider veins are commonly seen on the inner knee, whereas the arborizing pattern often appears on the outer thigh in a sunburst or cartwheel distribution.
Varicose veins - differ from spider veins in a number of ways. Varicose veins are larger - usually more than a quarter-inch in diameter, darker in color and tend to bulge. Varicose veins are also more likely to cause pain and be related to more serious vein disorders.