What causes varicose veins and spider veins?
Pooled blood enlarges the vein and it becomes varicose. According to the U.S. Department of Health & Human Services, spider veins can also be caused by the backup of blood. Hormone changes, inherited factors, and exposure to the sun can also cause spider veins.
The heart pumps blood filled with oxygen and nutrients to the whole body. Arteries carry blood from the heart towards the body parts. Veins carry oxygen-poor blood from the body back to the heart. The squeezing of leg muscles pumps blood back to the heart from the lower body.
Veins have valves that act as one-way flaps. These valves prevent the blood from flowing backwards as it moves up the legs. If the one-way valves become weak, blood can leak back into the vein and collect there. This problem is called venous insufficiency.