The walls of the veins are thinner, much less elastic and weaker then the walls of arteries. The veins start to enlarge most often in response to pressure on them and this creates a vicious cycle and a worsening venous condition. The pressure is typically from the forces of gravity, the bodies weight and the column of venous blood that has not yet finished its trip back to the heart. As a varicose vein enlarges it will contain larger volumes of blood, thus putting even greater pressure on the valve below. If the pressure becomes severe enough to exceed the strength of the valve, then the varicosity enlarges further, thus putting even more pressure on the next valve it encounters, as the condition continues to worsen.
Spider veins are the thread-like colored veins most often seen on the surface of the skin.
They occur most commonly in the legs but are often seen in the face and elsewhere. Some people desire treatment for cosmetic reasons only and others for the medical benefits it will provide to the legs. Without treatment the veins will enlarge and worsen with time. The circulatory system tends to suffer more disease with age, be it increasing hardening of the arteries, increased likelihood of heart attack or stroke, or a worsening of the veins. It may occur gradually or rapidly but the condition almost surely will become more severe Patients who seek treatment for medical reasons may fear problems in the future or may be symptomatic already.