Why does blood clot at a wound?
Short answer
When a blood vessel is injured, platelets gather and make an initial plug. A protein called fibrin then forms a mesh that reinforces the plug and helps slow or stop bleeding.
How it works
After a vessel is damaged, it narrows briefly to reduce blood loss. Platelets attach to the damaged area, change shape, and gather into a temporary plug. They also release signals that help activate the next steps.
Clotting factors then help produce fibrin, a long, sticky protein. Fibrin forms a mesh around the platelet plug, trapping blood cells and making the clot more stable. The clot is temporary and is later broken down as the wound is repaired.
Key point
Clotting at an injury protects the body, but unwanted clots inside blood vessels can cause health problems. This article is a basic explanation, not a diagnosis; seek medical advice for unusual bleeding, bruising, or other concerns.