Although the exact cause is unknown, there are some risk factors associated with the development of spider veins. These include:
Estrogen relaxing effect on vein walls. This may explain why women are more likely to get spider veins than men. The upsurge of hormones at puberty, birth control pills, pregnancy, and hormone replacement therapy all have been connected to the development of spider veins.
Injury seems to increase the chance of developing spider veins – even if the injury was years ago.
Prolonged periods of standing also will contribute to vein formation and support stockings are sometimes recommended.