Pulmonary embolism happens when a blood clot, usually formed in a deep vein of the leg, breaks loose and travels to the lungs. It can be life-threatening, but the good news is that most cases are preventable. Prevention comes down to keeping blood flowing, reducing clotting risk factors, and recognizing early warning signs before a clot has the chance to reach your lungs.
How Pulmonary Embolism Starts
Almost all pulmonary embolisms begin as deep vein thrombosis (DVT), a clot that forms in the large veins of the lower legs or thighs. Three conditions set the stage for clot formation: sluggish blood flow (from sitting still too long, for example), damage to the wall of a blood vessel, and blood that’s in a state more prone to clotting. When all three overlap, the risk climbs sharply. If part of a DVT clot breaks free, it rides through the bloodstream to the lungs, where it can block an artery and become a pulmonary embolism.
Understanding this chain of events is the key to prevention. Nearly every strategy below targets one or more of those three conditions.
Stay Moving Throughout the Day
Prolonged stillness is one of the biggest modifiable risk factors. When your legs stay in the same position for hours, blood pools in the deep veins of the calves and thighs. This is why clot risk rises after surgery, during long flights, and even during stretches of desk work.
If you’re able to walk, aim to get up and move for a few minutes every two to three hours when you’re sitting for extended periods. During flights or car rides longer than four hours, the CDC recommends choosing an aisle seat when possible so you can walk the cabin periodically, and building rest stops into road trips. Even small movements help: raise and lower your heels while keeping your toes on the floor, then reverse the motion by lifting your toes while your heels stay down. Tightening and releasing your calf muscles while seated also pushes blood upward through the veins.
Compression Stockings
Graduated compression stockings apply the most pressure at the ankle and gradually decrease pressure up the leg, which helps push blood back toward the heart. They’re available in several pressure ranges, but stockings in the 15 to 30 mmHg range are the most commonly used for clot prevention in otherwise healthy people. Higher-pressure stockings (30 to 40 mmHg or above) are typically reserved for people with a history of clots or chronic vein problems and are usually fitted by a healthcare provider.
In one trial of airline passengers over age 50, wearing below-knee compression stockings on flights longer than eight hours significantly reduced the formation of symptomless clots compared to flying without them. If you’re at higher risk due to age, a prior clot, or upcoming surgery, compression stockings are a simple, drug-free layer of protection.
Manage Your Weight
Carrying excess weight, particularly a BMI of 30 or above, increases the pressure on the veins in your pelvis and legs. That added pressure slows blood return from the lower body and contributes to the kind of sluggish flow that promotes clotting. Losing even a moderate amount of weight can improve venous circulation and reduce overall clot risk. Regular physical activity does double duty here: it helps with weight management while also keeping blood moving through the legs.
Quit Smoking
Smoking increases the risk of venous blood clots by roughly 23% compared to never smoking, according to a large meta-analysis published in PLOS Medicine. The effect appears to be driven by an acute mechanism, meaning the risk is tied closely to active smoking rather than long-term cumulative damage. That’s actually encouraging, because it means quitting has a relatively quick payoff. Former smokers had only a 10% elevated risk compared to never smokers, a meaningful drop from the 23% seen in current smokers. The researchers estimated that current smoking accounts for nearly 6% of all venous clot cases in the population.
Stay Hydrated
Dehydration thickens the blood and makes clotting more likely. This is especially relevant during air travel, where low cabin humidity accelerates fluid loss. Drinking water regularly before and during travel, and limiting alcohol and caffeine (which are mildly dehydrating), helps maintain normal blood viscosity. There’s no magic number of glasses per day that eliminates risk, but the principle is straightforward: if your urine is dark yellow, you need more fluids.
Be Aware of Hormonal Risk Factors
Estrogen-containing medications, including combined oral contraceptives and hormone replacement therapy, raise clotting risk. If you’re already at elevated risk due to obesity, smoking, a family history of clots, or a known clotting disorder, the combination can be significant. Talk with your prescriber about whether a lower-estrogen option or a non-hormonal alternative makes sense for you.
Pregnancy itself is a major risk factor for venous clots. One study found that 78% of pregnant individuals had at least one VTE risk factor, and roughly one in five developed new risk factors during labor and delivery that weren’t present earlier in pregnancy. For people with a prior history of clots, injectable blood thinners may be recommended during pregnancy and the postpartum period, though guidelines vary and the evidence is still being refined.
After Surgery: What to Expect
Surgery, especially orthopedic procedures like hip or knee replacement, is one of the highest-risk settings for clot formation. Hospitals typically use a combination of strategies: blood-thinning medications started before or shortly after the procedure, compression devices that inflate and deflate around your calves while you’re in bed, and early mobilization.
Getting out of bed and walking as soon as your surgical team gives the green light is one of the most effective things you can do. For high-risk surgeries like hip replacement or cancer operations, preventive blood thinners are often continued for four weeks after discharge, not just during the hospital stay. If you’re sent home with a prescription for a blood thinner, completing the full course matters, even if you feel fine.
Blood Thinners for Long-Term Prevention
If you’ve already had a pulmonary embolism or DVT, your doctor will likely prescribe anticoagulant therapy to prevent a recurrence. The initial treatment phase uses a higher dose to dissolve and stabilize the existing clot, then transitions to a lower maintenance dose for ongoing protection. How long you stay on blood thinners depends on what caused the clot. A clot triggered by a temporary event like surgery might only need three months of treatment, while an unprovoked clot or a second episode often calls for extended or even indefinite anticoagulation.
For people on long-term lower-dose blood thinners who experience a recurrent clot, current guidelines recommend stepping back up to the full therapeutic dose of the same medication rather than switching to a different class of drug.
Recognize the Warning Signs of DVT
Prevention also means catching a clot before it travels to the lungs. The classic signs of DVT include swelling in one leg (not both), pain or cramping that often starts in the calf, skin that looks red or purple over the affected area, and a feeling of warmth in the leg. These symptoms can be subtle, and DVT sometimes produces no noticeable symptoms at all.
If you notice unexplained swelling or persistent pain in one leg, especially after a period of immobility, surgery, or travel, getting it evaluated quickly is the single most important step you can take to prevent a pulmonary embolism. An ultrasound can confirm or rule out a clot in minutes, and early treatment with blood thinners is highly effective at keeping the clot from breaking loose.