Blood clots are part of the body’s natural defense system, sealing off injuries to stop bleeding. But sometimes, clots form without any injury—and that’s where the problems begin.

Picture your circulatory system like a busy highway. A deep vein thrombosis (DVT) is like a sudden traffic jam in that system, usually forming in the legs or arms. It blocks blood flow and can even break loose, potentially traveling to the lungs and becoming a pulmonary embolism, a life-threatening condition.

“Clots in the deeper veins can be dangerous because they interfere with circulation and may even break loose,” warns Dr. Luis Navarro, vascular specialist and founder of the Vein Treatment Center in New York.

The challenge? Many clots don’t announce themselves with obvious symptoms. Spotting subtle warning signs can make a crucial difference.

Warning Signs You Shouldn’t Ignore

Sudden Limb Swelling
If one leg or arm swells quickly for no clear reason, it could be a sign of DVT. “When a clot forms in a deep vein, it can obstruct blood flow, causing fluid to collect,” explains Dr. Navarro.

Persistent Cramping or Aching
Pain from a clot is often mistaken for a muscle strain or cramp. But unlike soreness from exercise, this discomfort tends to get worse when walking or flexing the foot.

Red or Warm Skin
If the skin turns red and feels warm, especially near the pain or swelling, it could be inflammation caused by a clot. “This type of redness tends to persist and may feel warm,” says Dr. Navarro.