Petechiae: Pinpoint flat round red spots under the skin surface caused by intradermal hemorrhage (bleeding into the skin). Petechiae are red because they contain red blood that has leaked from the capillaries into the skin. Petechiae are quite tiny (less than 3 millimeters in diameter) and do not blanch when pressed upon.
There are many conditions in which petechiae may be seen. These conditions range from very minor to very major. The common causes of petechiae include local injury and trauma, allergic reactions, autoimmune diseases, viral infections that impair blood coagulation (clotting), thrombocythemia (an abnormally low platelet level), certain medical treatments such as radiation and chemotherapy, idiopathic thrombocytopenic purpura (ITP), leukemia and other bone marrow malignancies that may lower the number of platelets, and sepsis (bloodstream infection). Petechiae are commonly seen right after birth in the newborn and after violent vomiting or coughing. Drugs such as the anticoagulants warfarin (Coumadin) or heparin, aspirin, and cortisone can also cause petechiae.