Blood clots form when three conditions overlap: sluggish blood flow, damage to a blood vessel wall, or changes in the blood’s chemistry that make it clot more easily. The good news is that most prevention strategies target at least one of these factors, and many are simple habits you can start today. Whether you’re preparing for surgery, a long flight, or just trying to lower your everyday risk, the basics are the same: keep your blood moving, stay hydrated, and know what puts you at higher risk.
Why Blood Clots Form
Your body forms clots as a repair mechanism. When you cut yourself, platelets and clotting proteins rush to seal the wound. Problems start when that process activates inside a healthy vein, most often in the legs, thighs, or pelvis. This is called deep vein thrombosis (DVT). If a piece of that clot breaks loose and travels to the lungs, it becomes a pulmonary embolism (PE), which can be life-threatening.
The three drivers of unwanted clots are slow blood flow (from sitting still, bed rest, or immobilization), irritation or injury to the vein wall, and blood that’s thicker or stickier than normal. Prevention works by addressing one or more of these triggers.
Move Your Legs Often
Sitting or lying still for hours is one of the biggest modifiable risk factors. When your calf muscles aren’t contracting, blood pools in your lower legs, and pooled blood clots more easily. The fix is straightforward: contract those muscles regularly.
If you’re stuck in a seat, ankle pump exercises are one of the most studied options. You simply point your toes down, then pull them back up toward your shin. A systematic review and network meta-analysis found that performing this movement once every 3 to 4 seconds is the most effective frequency for improving blood flow in the lower legs. You don’t need to do it nonstop, but running through a set of 20 to 30 pumps every 30 minutes makes a measurable difference.
When possible, get up and walk. Even a short lap around the office, cabin, or hospital hallway helps reset blood flow. If you work at a desk, set a timer to stand and move for a minute or two every hour.
Stay Hydrated
Dehydration thickens your blood. When you lose fluid through sweat, breathing, or simply not drinking enough, the water content of your plasma drops. That concentrates red blood cells, platelets, and clotting proteins, all of which make your blood more viscous and more prone to clotting. Research shows this effect is especially pronounced in warm or hot environments, where sweat losses are high.
Drinks that contain electrolytes and a small amount of carbohydrate restore blood volume more effectively than plain water or tea, because the body retains more of the fluid. That said, plain water is far better than nothing. A practical target for most adults is to drink enough that your urine stays pale yellow. On flights or in air-conditioned environments, where dry air accelerates fluid loss, make a conscious effort to drink more than you think you need.
Know Your Personal Risk Factors
Some clot risks are things you can’t change, like a family history of clotting disorders or a recent surgery. But several major risk factors are within your control or at least worth being aware of so you can take extra precautions.
- Excess weight. Being overweight or obese increases pressure on the veins in your legs and pelvis, slowing return blood flow.
- Estrogen-containing medications. Birth control pills, patches, and rings that contain estrogen raise clot risk, as does hormone replacement therapy after menopause. If you have other risk factors, talk to your prescriber about alternatives.
- Pregnancy and postpartum. Clot risk is elevated throughout pregnancy and for up to three months after giving birth, partly because of hormonal shifts and partly because the growing uterus compresses pelvic veins.
- Prolonged immobility. Hospital bed rest, a leg cast, or even sitting with crossed legs for hours at a time all slow blood flow enough to matter.
- Smoking. Smoking damages blood vessel walls and makes blood stickier. Quitting removes that ongoing irritation.
The more of these factors you stack, the higher your overall risk. Someone who is overweight, takes estrogen-containing birth control, and sits at a desk all day has a meaningfully different risk profile than someone with just one of those factors.
What to Do on Long Trips
Any trip lasting more than four hours, whether by plane, car, bus, or train, raises your risk of a blood clot. The combination of cramped seating, low cabin humidity (on flights), and hours of stillness creates ideal conditions for sluggish blood flow.
A few practical steps reduce that risk significantly. Get up and walk the aisle or stop the car every one to two hours. While seated, do ankle pumps and calf raises regularly. Avoid crossing your legs, which further compresses veins. Drink water before and during the trip, and skip alcohol, which is dehydrating. If you have additional risk factors, graduated compression stockings with 18 to 23 mmHg of pressure at the ankle are the standard recommendation for prevention. These are available without a prescription at most pharmacies.
Compression Stockings
Graduated compression stockings work by applying the most pressure at the ankle and gradually less pressure as they move up the leg. This design helps push blood upward toward the heart, counteracting the pooling effect of gravity and immobility.
For prevention in people who don’t already have a clot, the recommended pressure at the ankle is 18 to 23 mmHg. That’s a lighter squeeze than the 30 to 40 mmHg stockings used to treat existing clot damage. Wearing the right level matters: too loose and they won’t help, too tight and they can actually restrict flow. Make sure they fit well and don’t bunch or roll down, which can create a tourniquet effect behind the knee.
Compression stockings are commonly recommended after surgery, during long travel, and for people who stand or sit for extended periods at work.
Foods That Support Healthy Blood Flow
Your diet won’t replace medical prevention if you’re at high risk, but certain foods have measurable effects on platelet activity. Garlic, onions, tomatoes, and beetroot have all been studied for their ability to reduce platelet clumping, which is one of the early steps in clot formation. These effects come from natural compounds in these vegetables that make platelets less “sticky.”
You don’t need to eat them in supplement form. Regular inclusion in your meals, think a tomato-based sauce, roasted garlic, or a beet salad a few times a week, contributes to a dietary pattern that supports cardiovascular health more broadly. Pairing these foods with adequate hydration and regular movement gives you a practical, low-effort foundation for clot prevention.
When Medication Is Part of the Plan
For people at higher risk, especially after major surgery, during a hospital stay, or after a first clot, doctors often prescribe blood-thinning medication. These work by interfering with the clotting process, either by slowing platelet activity or by blocking clotting proteins in the blood. The type and duration depend on your specific situation. Some people take a blood thinner for a few weeks after surgery, while others with recurrent clots or clotting disorders may stay on one long-term.
If you’re prescribed a blood thinner, the most important practical consideration is consistency. Missing doses creates gaps in protection, and the medication only works while you’re taking it. You’ll also bruise more easily and bleed longer from cuts, which is a normal trade-off, not a side effect to worry about unless bleeding is heavy or won’t stop.
Warning Signs to Recognize
Even with good prevention habits, clots can still happen. Knowing the warning signs means you can act fast if one does form.
DVT in a leg or arm typically causes swelling, pain or tenderness, warmth, and redness or discoloration in the affected limb. The symptoms usually appear in just one leg, not both, which helps distinguish a clot from general swelling or muscle soreness.
A pulmonary embolism feels different. The hallmark symptoms are sudden difficulty breathing, chest pain that worsens when you take a deep breath or cough, a rapid or irregular heartbeat, coughing up blood, and feeling lightheaded or faint. PE is a medical emergency. If you or someone near you develops these symptoms, call emergency services immediately.