If you are logging hours in the car or on a plane this season, you could be at higher risk for deep vein thrombosis (DVT), a type of blood clot that forms in the leg veins. Your risk of developing DVT increases when are sitting still for a long period of time, such as when you are traveling or bedridden after a surgery or injury.

"The condition occurs when blood pools in your lower extremity veins, which can happen when the calf muscles are not being used," says Garnet Craddock, M.D., a vein care specialist at Piedmont.

Deep vein thrombosis is a serious medical condition

DVT can turn deadly if the clot breaks off from inside the vein and travels to the lungs, which can lead to a pulmonary embolism. Deep vein thrombosis and pulmonary embolism are categorized together as venous thromboembolism (VTE), which is the third leading cause of cardiovascular illness.

"People with DVT are at about 30 percent risk of a second DVT in 10 years," says Dr. Craddock. "Many DVT patients are asymptomatic, so the true incidence is not well-defined, but there are about 275,000 new VTE cases per year."

Deep vein thrombosis risk factors

Several factors can increase your risk of DVT:

• Travel (Dr. Craddock's rule of thumb is more than two hours by car or one hour by plane)

• Older age

• Being a woman in her childbearing years

• Obesity

• Previous history of clotting issues

• Oral contraceptives (particularly birth control with higher estrogen content)

• Underlying clotting disorders

• Recent surgery or trauma (limits your ability to take preventive low-dose blood thinners and limits your mobility)

• Pregnancy

• Cancer (30 percent of cancer patients develop DVT)

• Certain illnesses

Symptoms of deep vein thrombosis

DVT often has no symptoms. If symptoms occur, they include:

• Swelling in the affected leg and rarely, swelling in both legs

• Soreness or cramping in the calf muscle

How to prevent deep vein thrombosis

Dr. Craddock recommends the following measures to prevent travel-related DVT:

• Wear gradient compression hose covering the ankle and knee.

• Increase your mobility during travel with frequent calf movement while sitting. Pump your legs and wiggle your toes.

• Take short walks every one to two hours during travel. If you are on a plane, walk up and down the aisles.

• Stay well hydrated with water and avoid drinking alcohol.

• Talk to your doctor about blood thinners for a long trip if you are at higher risk for DVT.

"Taking aspirin for DVT prevention is controversial and not a well-proven method," says Dr. Craddock. "It is often used as a preventive measure when people travel, but it should not be the only preventive measure you take."

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