Blood Clots: Signs, Causes, and What to Do

A blood clot can start quietly in your leg and turn dangerous fast. If you’ve ever felt unexplained swelling or sudden shortness of breath, don’t shrug it off. This guide tells you what to look for, what causes clots, and the clear steps to take right away.

What causes blood clots and who’s at risk

Clots form when blood thickens and sticks together. That’s helpful for a cut, but harmful inside a vein. Common triggers are periods of low movement (long flights, bed rest), recent surgery, cancer, pregnancy, some birth control pills, obesity, and smoking. Older age and family history of clotting problems raise risk, too. Certain medicines and dehydration also play a role.

Genetic clotting disorders exist — if you’ve had more than one unexpected clot, ask your doctor about testing for things like Factor V Leiden or prothrombin gene changes.

How to recognize a dangerous clot fast

Not every ache is a clot. Look for clear warning signs: one leg suddenly swollen, warm, red, and painful (deep vein thrombosis or DVT). Or sudden shortness of breath, sharp chest pain that gets worse with breathing, lightheadedness, or coughing up blood — those suggest a pulmonary embolism (PE), when a clot travels to the lungs. If you see these, get emergency care immediately.

Do not try to massage the area or keep exercising through severe pain. Avoid waiting it out. Quick diagnosis and treatment cut the risk of serious damage.

Doctors use simple tests: an ultrasound for leg clots, a D-dimer blood test to flag clotting activity, and CT pulmonary angiography for suspected lung clots. Your doctor will choose the right test fast based on symptoms.

Treatment usually starts with blood thinners (anticoagulants) such as heparin in the hospital, followed by oral options like warfarin or direct oral anticoagulants (apixaban, rivaroxaban). In urgent cases, doctors may remove the clot or use clot-busting drugs. Follow-up care and the length of treatment depend on why the clot happened and your personal risk.

Prevention is practical. On long trips, stand and walk every hour, drink water, and consider compression socks if you’re at risk. After surgery, follow mobilization advice and take prescribed blood thinners. Quit smoking, manage weight, and review medications with your doctor if you have risk factors.

If you’re unsure whether something counts as a warning sign, call your doctor or a local urgent care. It’s better to check and be safe. Blood clots can be treated effectively when caught early — knowing the signs and acting fast makes the difference.