The increased pressure caused by pooling stretches the vein, enlarging it, and twisting the blood vessels. This is what creates the bumpy, rope-like appearance of your veins.
There are a series of factors that can trigger the onset of varicose veins including prolonged standing, hormones, pregnancy, obesity, aging, or menopause. Varicose veins are hereditary. Normally, they are found in women, but almost anyone can develop them.