If you are pregnant or have just had a baby, your risk is also higher. Similarly, if you have an inflammatory condition such as Crohn’s disease or rheumatoid arthritis, this can increase your risk of clots.
Being older than 60 increases your risk of deep vein thrombosis, though it can occur at any age.
If you are at higher risk you should not drink lots of alcohol as this can make you dehydrated, and more prone to clots. If you smoke it also increases your risk. Smoking affects blood clotting and circulation, which can increase your risk.
Sometimes, a blood clot in a vein can occur with no apparent underlying risk factor.