Petechiae Petechiae are pinpoint-sized reddish/purple spots, resembling a rash, that appear just under the skin or a mucous membrane when capillaries have ruptured and some superficial bleeding into the skin has happened. This term refers to an abnormally increased susceptibility to developing petechiae. SNOMEDCT_US:50091001 HP:0000967 UMLS:C0031256 SNOMEDCT_US:271813007 MEDDRA:10034754 Macular purpura