World Hemophilia Day 2025: Causes of blood clot without injury and how to prevent it

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Blood clotting is a vital process that helps prevent excessive bleeding when you’re injured. According to the American Society of Hematology, platelets and proteins in your blood work together to form a clot and seal the wound. Normally, the body breaks down the clot once the injury heals. But sometimes, clots form without an injury or don’t dissolve on their own, this can lead to serious health issues.

According to multiple studies, clots can form in either veins or arteries. Veins return blood to the heart, and when a clot forms in a vein, like in deep vein thrombosis (DVT), it can block blood flow and cause swelling or pain. If part of the clot travels to the lungs, it can lead to a pulmonary embolism (PE), which is a life-threatening condition that needs immediate treatment.

Blood clots might seem like rare or distant concerns, but they can develop silently and dangerously, says Dr Narendra Agrawal, Unit Head & Sr. Consultant, Hemato-Oncology at Rajiv Gandhi Cancer Institute & Research Centre (RGCIRC). “Blood clotting is the body’s natural defense mechanism to stop bleeding. But when clots form without injury, or worse, block major blood vessels, it can lead to serious conditions like deep vein thrombosis (DVT), stroke, or heart attack,” he says.

Causes of deep vein thrombosis (DVT): Sitting still for too long, such as on intercontinental flights or after orthopedic surgery, slows blood flow and increases clotting risk. Moving around at regular intervals helps prevent this (Image: Canva)

Also read | Deep vein thrombosis: Here's why you should worry about blood clots if you sit for too long

According to Dr Agarwal, one of the less talked about but critical causes of spontaneous clotting is undiagnosed cancer. “In some cases, a blood clot might actually be the first symptom that leads to a cancer diagnosis. Additionally, prolonged immobility, certain surgeries, and genetic conditions can all increase clotting risk without immediate signs,” he says.

Cancer-related clotting can be complicated. Inflammation from cancer or its treatments raises the risk of thrombosis, making clot management a vital part of cancer care. “Some patients develop clots even before cancer is diagnosed. Others might experience clotting during chemotherapy or recovery. In high-risk cases, preventive anticoagulation medication is given to avoid complications,” Dr Agrawal says.

It it’s crucial to understand the importance of early recognition and proactive care, especially when the symptoms are vague or go unnoticed.

Dr Agarwal lists the following common but surprising reasons for blood clots, and also suggests ways to prevent it:

• Congenital clotting disorders: Some people are born with defects in their blood's clotting proteins. These rare genetic issues, known as congenital coagulopathies, can cause blood to clot excessively without any injury or trauma.

• Hidden cancers and inflammation: Increased inflammation from certain cancers can silently trigger clots, says Dr Agrawal. “Swelling in the legs or unexplained pain in the abdomen may sometimes point to an underlying malignancy,” he says.

• Long periods of immobility: Sitting still for too long, such as on intercontinental flights or after orthopedic surgery, slows blood flow and increases clotting risk. Moving around at regular intervals helps prevent this.

• Certain surgeries and medications: Post-operative patients, especially those who’ve had joint replacements, are often given blood thinners to prevent clots. “Some medications, including hormone-based therapies, can also increase clot risk,” he says.

• Smoking and poor diet: Smoking damages blood vessels and promotes clot formation. Diets high in processed food and low in nutrients further fuel inflammation, increasing risk.

Everyday habits that support healthy circulation:

• Move more: Whether you’re at work or on a flight, stretch your legs every hour or so.
• Eat greens: Vitamin K from leafy vegetables regulates clotting factors in your blood.
• Add more colour to your plate: Fruits and vegetables rich in antioxidants support blood vessel health.
• Get your omega-3s: Nuts, seeds, flaxseed, and fatty fish like salmon lower inflammation and clotting tendencies.
• Use natural blood helpers: Garlic and ginger, when eaten regularly, help keep platelets from sticking together.
• Stay hydrated: Dehydration can thicken the blood, making clots more likely.
• Know your family history: If you have a genetic predisposition, inform your doctor and stay vigilant.