Varicose veins are enlarged veins that usually occur just under the skin (superficial veins). Varicose veins are likely to be caused by one or more factors, including:

• Increased pressure in the leg veins.
• Damage to the leg veins.
• Damage to the valves of the leg veins.

Varicose veins often run in families. You may be born with defective valves or weak walls in your veins, or you may develop them later in life.

Pregnancy is a common cause of varicose veins. During pregnancy, hormones relax the veins and more blood travels through the veins. Extra weight and a heavy uterus place pressure on leg veins, too.

Less commonly, varicose veins may be a sign of a more serious problem that may sometimes need treatment. These serious problems can include:

• Blood clots or blockage in the deep veins or perforating veins.
• Injury to the deep veins.
• Abnormal blood vessels between arteries and veins (arteriovenous fistulas). A person may be born with these problems or develop them later in life.
• Tumors (very rarely).