Varicose veins are a condition in which the blood vessels in your legs become swollen and blue or black. This occurs when the valves in the veins that return blood to the heart become weak. The main causes are:
Working for long periods of time: Standing for hours on end puts excessive pressure on the veins in your legs. This prevents blood from flowing upward and causes blood to pool in the veins and cause them to swell.
Aging: As you age, the elasticity of the blood vessels decreases and the valves inside weaken. This causes blood to flow backward (reflux).
Obesity and lack of exercise: When you gain weight, the veins in your legs become more stressed than they can handle. Reduced physical activity slows down blood flow in your legs.
Pregnancy: During pregnancy, the increased blood volume in the body and the pressure of the uterus on the veins increase the risk of varicose veins. Hormonal changes also cause the veins to dilate.
Heredity: If someone in the family has this problem, others are more likely to develop it. The natural weakness of the vein walls can be inherited.