A blood clot in your leg, known as deep vein thrombosis (DVT), causes swelling, pain, and warmth in the affected area. Left untreated, the clot can break free and travel to your lungs, creating a life-threatening emergency called a pulmonary embolism. Most people recover well with treatment, but the clot can leave lasting damage to the veins in your leg.
How a Clot Forms in Your Leg
Blood clots in the leg typically start in the deep veins, most often near the valves that keep blood flowing upward toward your heart. These valve pockets are prone to sluggish blood flow, which can starve the vein lining of oxygen. When that happens, the inner wall of the vein becomes “sticky,” attracting white blood cells and tiny cell fragments called platelets. Those cells trigger a chain reaction that produces fibrin, a protein that acts like a mesh net, trapping blood cells into a solid mass.
The clot can stay small or continue growing along the vein. As it gets larger, it blocks more blood flow, which is what causes the symptoms you feel in your leg.
What It Feels Like
The most common symptom is swelling in one leg. You may also notice pain or cramping that often starts in the calf and feels like a deep soreness or tightness. The skin over the clot may feel noticeably warm to the touch, and it can change color to red or purple depending on your skin tone. Some people describe tenderness when pressing on the swollen area.
Not everyone gets all of these symptoms. Some DVTs cause only mild swelling or a vague ache that’s easy to dismiss as a pulled muscle. Roughly half of DVT cases produce minimal symptoms, which is part of what makes the condition dangerous.
The Biggest Danger: Pulmonary Embolism
The most serious complication is when part or all of the clot breaks loose, travels through the bloodstream, and lodges in the blood vessels of your lungs. This is a pulmonary embolism (PE), and it can be fatal.
A large clot can block the main artery feeding your lungs, cutting off blood flow and putting enormous strain on your heart. Smaller fragments tend to travel deeper into the lungs, blocking smaller vessels and causing sharp chest pain that worsens when you breathe. The classic signs of a PE are sudden shortness of breath, chest pain, and a rapid heart rate. Some people also experience sweating, fever, or coughing up blood.
If you have leg symptoms consistent with DVT and then develop sudden chest pain or difficulty breathing, that combination is a medical emergency. Call 911 or go to an emergency room immediately.
What Raises Your Risk
Blood clots in the leg are often “provoked,” meaning something specific triggered them. The most common triggers fall into a few categories:
- Surgery and immobilization: Operations lasting more than 45 minutes (especially orthopedic, abdominal, or pelvic surgeries) are a major risk factor. Being bedridden for more than 72 hours triples your risk of a clot.
- Trauma: Injuries to the leg, including fractures and even minor injuries requiring a cast, can set off clot formation, particularly in people with inherited clotting tendencies.
- Hormones: Birth control pills, hormone replacement therapy, and pregnancy all increase clotting risk.
- Cancer: Active cancer is one of the strongest persistent risk factors for DVT.
- Long travel: Sitting for hours on a long flight or car ride slows blood flow in your legs enough to raise your risk.
Some clots happen without an obvious trigger. These “unprovoked” DVTs may be linked to underlying conditions like obesity, heart failure, inflammatory bowel disease, or simply getting older. Genetic clotting disorders like Factor V Leiden also play a role, though testing for these doesn’t always change how the clot is treated.
How DVT Is Diagnosed
If your doctor suspects a blood clot, the first step is usually a blood test that measures a substance called D-dimer, which rises when your body is actively breaking down clots. A normal D-dimer level makes DVT very unlikely. If the level is elevated, you’ll get an ultrasound of your leg. The technician presses the ultrasound probe against the vein. A healthy vein compresses flat, while a vein containing a clot stays rigid. This compression ultrasound is the standard imaging test and is painless.
What Treatment Looks Like
The main treatment is blood-thinning medication (anticoagulants). These drugs don’t dissolve the clot. Instead, they prevent the clot from growing and stop new clots from forming, giving your body time to gradually break the clot down on its own.
Most people start treatment the same day they’re diagnosed and take blood thinners for at least three months. If the clot was unprovoked or you have ongoing risk factors like cancer, your doctor may recommend staying on the medication longer, sometimes indefinitely. The biggest side effect to watch for is bleeding, since the medication slows your body’s ability to form clots anywhere, not just in your leg.
In severe cases where a very large clot threatens blood flow to the leg or lungs, doctors may use clot-dissolving drugs or a catheter-based procedure to physically remove the clot. These are reserved for emergencies.
Walking and Activity After Diagnosis
One of the most common concerns after a DVT diagnosis is whether moving around will dislodge the clot. Multiple clinical trials have shown that early walking after diagnosis, once you’ve started blood thinners, does not increase the risk of pulmonary embolism. In fact, walking may help reduce acute symptoms like pain and swelling.
Research on patients with prior DVT found that 30 minutes of vigorous treadmill exercise did not worsen vein-related symptoms and actually improved calf muscle flexibility. So while your instinct might be to stay off your feet, staying active is both safe and beneficial once treatment is underway.
Long-Term Effects on Your Leg
Even after the clot resolves, the damage it caused to the vein and its valves can create lasting problems. Between 20% and 50% of people who’ve had a DVT develop a condition called post-thrombotic syndrome (PTS) within a year or more. PTS happens because the clot scars the vein walls and destroys the one-way valves that normally push blood upward, allowing blood to pool in the lower leg.
Typical symptoms include chronic pain, swelling, heaviness, and fatigue in the affected leg. Many people notice itching and nighttime cramping. The skin around the ankle may develop a brownish discoloration, become dry or scaly, or show new varicose veins.
About 5% to 10% of DVT patients develop severe PTS, which can include open sores (venous ulcers) on the lower leg that are slow to heal. One long-term study found that nearly 5% of DVT patients developed a venous ulcer within 10 years. Compression stockings, regular exercise, leg elevation, and maintaining a healthy weight are the main strategies for managing PTS symptoms and preventing them from worsening.