To understand what causes varicose veins it is first useful to understand how blood is circulated around your body.

Circulation system

The system that controls your circulation is made up of arteries and veins. Your arteries carry blood from your heart to the organs and tissues in your body. Veins return the used blood back to your heart.

In order to return the blood, your veins must work against gravity. The muscles in your leg contract, helping to pump the blood back towards your heart.

Weakened valves

Inside your veins are tiny one-way valves that open to let the blood through and then close to prevent it flowing backwards.

Sometimes, the walls of the veins can become stretched and lose their elasticity, causing the valves to become weakened. If the valves do not function properly, this can cause the blood to leak and flow backwards. If this happens, the blood will collect in your veins, which will become swollen and enlarged.

The reasons why the walls of the veins stretch and the valves in your veins weaken are not fully understood. Some people develop the condition for no obvious or apparent reason.

Risk factors

There are a number of risk factors that can increase your likelihood of developing varicose veins, including:

• gender
• genetics
• age
• being overweight
• occupation
• being pregnant

These risk factors are discussed in more detail below.

Gender

Women are more likely to be affected by varicose veins than men. Research suggests that this may be because female hormones tend to relax the walls of veins, making the valves more prone to leaking. Hormones are chemicals that are produced by the body.

Genetics

Your risk of developing varicose veins is increased if a close family member has the condition. This suggests that varicose veins may be partly caused by your genes (the units of genetic material that you inherit from your parents).

See the Health A-Z topic about Genetics for more information about how you inherit your physical and behavioural characteristics.

Age

As you get older, your veins start to lose their elasticity and the valves inside them stop working as well.

Being overweight

Being severely overweight puts extra pressure on your veins, which means they have to work harder to send the blood back to your heart. This can put increased pressure on the valves, making them more prone to leaking.

You can use the healthy weight calculator to check whether you are overweight.

Occupation

Some research suggests that jobs that require long periods of standing may increase your risk of getting varicose veins. This is because your blood does not flow as easily when you are standing for long periods of time.

Pregnancy

When a woman is pregnant, the amount of blood in her body increases to help support the developing baby. This puts extra strain on your circulatory system. Increased hormone levels during pregnancy also cause the muscular walls of the blood vessels to relax. Both of these factors may increase your risk of developing varicose veins.

Varicose veins may also develop during pregnancy as the womb (uterus) begins to grow. As the womb expands it puts pressure on the veins in your pelvic area, which can sometimes cause them to become varicose.

Although being pregnant can increase your risk of developing varicose veins, most women find that the condition significantly improves after their pregnancy. See the Pregnancy care planner for more information about preventing varicose veins during pregnancy.