Spider veins occur due to different reasons in different people. Various factors which lead to abnormal blood flow and weakens the walls of the vein causes the formation of these veins because increased pressure on these veins makes them dilate and appears like spider veins. Among various factors hormonal changes is the most common reason for these veins. The hormonal changes may be due to menopause, pregnancy, hormone therapy, puberty, birth control pills and others.

The spider veins in women who experience temporary changes in hormones like pregnancy fades after the birth of the child. Hereditary is also one of the reason which causes these veins and if an individual has a family history of it then the chances become more prominent. Overweight people also tend to get spider veins as their weight puts pressure on these veins and leads to their swelling. Prolonged standing can also be a reason, because standing at one place for a long period of time increases pressure n the veins and dilates them. Besides these there are many other factors like advance aging, exposure to ultraviolet rays, sitting with legs crossed for a long period of time, trauma or injury to the skin, wearing tight undergarments and clothes and many others.