Also known as varicosities, varicose veins are abnormally widened veins that are swollen, dark and frequently twisted or contorted instead of straight. They are more common in the superficial veins (just under the skin) than the deep veins (embedded deep in the muscles), although they can occur in either. Varicose veins are often noticeable at the back of the calf and thigh and may be surrounded by groups of flooded capillaries called spider veins (telangiectases).

Other types of varicose veins include:

• Venous lakes. These are small collections of blood that pool within the veins. They are typically found on the neck and face.
  
  
• Reticular veins. These veins often appear behind the knee and appear as flat, blue veins.
  
  
• Telangiectasia. These reddish veins are as thin clusters of blood vessels, similar to spider veins. They often appear on the upper body or face.

Arteries and blood vessels work to circulate blood throughout the body. Arteries carry blood from the heart to tissues while veins return blood from parts of the body to the heart. For blood to travel from the legs to the heart, muscle contractions work against the vein walls to move the blood. As individuals age, the veins in the body lose their elasticity, reducing the movement of blood. Varicose veins may be caused by either increased blood pressure in the veins or damage, weakness or failure of the valves within the vein.

The valves are responsible for keeping blood flowing in the right direction, which is particularly important when the veins are counteracting the effects of gravity to bring oxygen-poor blood from the legs to the heart. The valves close to prevent blood from flowing away from the heart in the veins (regurgitation). Leaky or damaged valves can cause blood to pool in the legs, resulting in swollen, varicose veins. Damage to the valves may be caused by a blood clot, a congenital defect (a defect present since birth) or chronic venous insufficiency.

Risk factors for varicose veins include:

• Being born with weak leg valves
• Advanced age
• Family history of varicose veins
• Hormonal changes (e.g., menopause, puberty)
• History of deep vein thrombosis
• Pregnancy, especially during the first and last trimesters
• Standing in one position for long periods of time
• Obesity
• A tumor in the abdomen

Varicose veins affect about half of people over the age of 50. The condition is more common in women, according to the U.S. National Institutes of Health (NIH). Although varicose veins usually occur in the legs, they can also occur around the anus (hemorrhoids), in the vulva of a pregnant woman and around a man’s scrotum (varicocele).