Veins carry blood from different parts of your body back to your heart. Your leg muscles squeeze to send blood back to your heart against the push of gravity. Veins in your body contain valves that ensure blood flow moves in one direction and doesn’t accumulate or flow backward. If you have faulty, damaged, or weak valves in your veins, blood can build up and cause enlarged veins that appear as spider veins on your skin and cause pain. Some factors that can increase your risk of developing spider veins include: • Increasing age • Hormonal changes (such as during pregnancy) • Injuries • Obesity • Lack of physical activity • Medical history (being born with faulty valves) • Genetics