Petechiae are small, pinpoint-sized red or purple spots that appear on the skin or mucous membranes. They occur when tiny blood vessels, called capillaries, break and leak blood into the surrounding tissue. These spots do not blanch or fade when pressed and can vary in size. Petechiae can be caused by various factors, including infections, allergic reactions, or blood disorders. While they are often harmless, their presence can sometimes indicate a more serious underlying condition, so it is important to consult a healthcare professional if they appear unexpectedly or in large numbers.