Which characteristic of aspirin causes bleeding?

Aspirin causes bleeding primarily due to its antiplatelet effects, which inhibit the function of platelets in the blood. It irreversibly blocks the enzyme cyclooxygenase-1 (COX-1), leading to decreased production of thromboxane A2, a molecule essential for platelet aggregation. This reduction in platelet aggregation impairs the blood's ability to form clots, increasing the risk of bleeding, particularly in the gastrointestinal tract and during surgical procedures.