Cause of Varicose Veins and Spider Veins
Varicose veins can be caused by weak or damaged valves in the veins. The heart pumps blood filled with oxygen and nutrients to the whole body through the arteries.
Veins then carry the blood from the body back to the heart. As your leg muscles squeeze, they push blood back to the heart from your lower body against the flow of gravity.
Veins have valves that act as one-way flaps to prevent blood from flowing backwards as it moves up your legs.
If the valves become weak, blood can leak back into the veins and collect there. (This problem is called venous insufficiency.) When backed-up blood makes the veins bigger, they can become varicose.
Spider veins can be caused by the backup of blood. They can also be caused by hormone changes, exposure to the sun, and injuries.