Unlike arteries, veins have flaps inside called valves. When your muscles contract, the valves open, and blood moves through the tubes. When your muscles relax, the valves close so the blood flows in only one direction.


Damaged valves may not close the way they should when your muscles relax. This allows blood to flow in both directions, and it can pool.

This is what happens with varicose veins. They may bulge like purple ropes under your skin. They can also look like small red or purple bursts on your knees, calves, or thighs. These spider veins happen because of swollen small blood vessels called capillaries. After a day of activity, your legs might ache, sting, or swell.

More women than men get varicose veins, and they often run in families. Pregnancy, being very overweight, or standing for long times can cause them.

Because your blood is moving more slowly, it may stick to the sides of your veins, and clots can form.