Deep vein thrombosis (DVT) is a condition that occurs when blood clots form in veins deep inside your body. These clots can occur anywhere in the body. However, this condition often affects the lower legs or thighs.

Symptoms of DVT include swelling, pain or tenderness, and skin that may feel warm to the touch.

DVT can happen to anyone. But you have a greater risk of developing DVT after a surgery or trauma. Being overweight and smoking are also risk factors.

DVT is a serious condition because a blood clot can travel to the lungs and block an artery. This is called a pulmonary embolism. Risk for this condition is also higher after a surgery.

Since DVT can lead to serious complications, your doctor may recommend DVT compression stockings to reduce swelling and improve blood flow to your heart and lungs. If you’re not familiar with how these stockings work, here’s what you need to know.

Compression stockings are like pantyhose or tights, but they’re made from a different material and serve a different purpose.

While you may wear ordinary stockings for style or to protect your legs, compression stockings have an elastic fabric designed to fit tightly around the ankles, legs, and thighs. These stockings are tighter around the ankle and less tight around the calves and thighs.

The pressure created by the stockings pushes fluid up the leg, which allows blood to flow freely from the legs to the heart. Compression stockings not only improve blood flow, but also reduce swelling and pain. They are particularly recommended for the prevention of DVT because the pressure stops blood from pooling and clotting.

Compression stockings are effective for preventing DVT. Studies examining the effectiveness of compression stockings have found a link between compression stockings and DVT prevention in hospitalized patients.

One study followed 1,681 people and consisted of 19 trials, including nine with participants undergoing general surgery and six with participants undergoing orthopedic surgery.

Among those wearing compression stockings before and after surgery, only 9 percent developed DVT, compared with 21 percent of those who didn’t wear compression stockings.

Similarly, a study comparing 15 trials found that wearing compression stockings could reduce the risk of DVT by as much as 63 percent in surgical cases.

Compression stockings don’t just prevent blood clots in those who’ve had surgery or trauma. Another study concluded that these stockings could also prevent DVT and pulmonary embolism in people on flights of at least four hours. Blood clots in the legs can form after a long flight due to prolonged sitting in a confined space.

If you experience leg trauma or have surgery, your doctor may prescribe compression stockings for use during your hospital stay or at home. You can purchase these from a pharmacy or a medical supply store.

These stockings can be worn after a DVT diagnosis to alleviate some of the discomfort and swelling. Previously, compression stockings were used after an acute DVT to help prevent a condition called post-thrombotic syndrome (PTS) which can manifest as chronic swelling, pain, skin changes, and ulcers on the lower extremity. However, this is no longer the recommendation.

Compression stockings may also be worn as a preventative measure.

For best results, put on compression stockings first thing in the morning before you stand on your feet and begin moving. Moving around can cause swelling, at which point it may become harder to put on the stockings. Keep in mind that you’ll have to remove the stockings before showering.

Since compression stockings are elastic and tight, applying lotion to your skin before putting on the stockings can help the material glide up your leg. Make sure the lotion fully absorbs into your skin before attempting to put on the stockings.

To put on a compression stocking, grab the top of the stocking, roll it down toward the heel, put your foot inside the stocking, and then slowly pull the stocking up over your leg.

Wear the stockings continuously throughout the day, and don’t remove it until bedtime.

Wash the stockings after each use with mild soap, and then air dry it. Replace your stockings every four to six months.

Compression stockings come in different levels of tightness, so it’s important to find stockings with the right amount of pressure. Choose between knee-high, high-high, or full-length stockings. Your doctor may recommend a knee-high if you have swelling below the knee, and a thigh-high or full-length if you have swelling above the knee.

Even though your doctor can write a prescription for compression stockings, you don’t need a prescription for stockings up to 20 mmHg (millimeters of mercury). Millimeters of mercury is a measurement of pressure. Stockings with higher numbers have a higher level of compression.

The recommended tightness for DVT is between 30 and 40 mmHg. Compression options include mild (8 to 15 mmHg), moderate (15 to 20 mmHg), firm (20 to 30 mmHg), and extra firm (30 to 40 mmHg).

The right amount of tightness is also necessary for the prevention of DVT. Compression stocking sizes vary by brand, so you’ll need to take body measurements and then use a brand’s sizing chart to determine the right size for you.

To find your size for knee-high stockings, measure the circumference of the narrowest part of your ankle, the widest part of your calf, and your calf length starting from the floor to the bend of your knee.

For thigh-high or a full-length stockings, you’ll also need to measure the widest part of your thighs and your leg length starting from the floor to the bottom of your buttocks.

DVT can cause pain and swelling. It can be a potentially life-threatening condition if a blood clot travels to your lungs. Learn how to recognize symptoms of this condition, especially if you’ve recently taken a long trip, experienced trauma, or had surgery. Seek treatment if you suspect a blood clot in your legs.

If you have an upcoming surgery or plan on taking a long trip, ask your doctor about wearing compression stockings to help prevent DVT.