Petechia and purpura on the low limb due to medication induced vasculitis.
"Petechiae" refers to one of the three major classes of purpuric skin conditions. Purpuric eruptions are classified by size into three broad categories. Petechiae is generally used to refer to the smallest of the three classes of purpuric skin eruptions, those that measure less than 3 mm.
The most common cause of petechiae is through physical trauma such as a hard bout of coughing, vomiting or crying, which can result in facial petechiae, especially around the eyes. Petechiae in this instance are harmless and usually disappear within a few days. Petechiae may be a sign of thrombocytopenia (low platelet counts) when platelet function is inhibited (e.g., as a side effect of medications or during certain infections), or in clotting factor deficiencies. They may also occur when excessive pressure is applied to tissue (e.g., when a tourniquet is applied to an extremity or with excessive coughing or vomiting).
If unsure, petechiae should always be quickly investigated. They can be interpreted as vasculitis, an inflammation of the blood vessels, which requires immediate treatment to prevent permanent damage. Some malignancies can also cause petechiae to appear. Petechiae should be investigated by a doctor to rule out the more dangerous conditions. Dermatologists can be the most helpful specialists in these conditions because they can more easily identify if the condition is petechiae or some similar looking but less worrisome rash.
The significance of petechiae in children depends on the clinical context in which they arise. Petechiae in children can occur with viral infections. In this instance, they do not necessarily signify a serious illness. However, they are a hallmark signal of some potentially serious illnesses, such as meningococcemia, leukemia, and certain causes of thrombocytopenia, of which meningococcemia can cause death within 48 hours of infection. Therefore, their presence should not be ignored.
Petechiae (in the face) may also be present in cases of self asphyxiation.
List of associated conditions 
- Bartonella - Cat Scratch Disease
- Bolivian hemorrhagic fever
- Boutonneuse fever
- Cerebral malaria
- Congenital syphilis
- Crimean–Congo hemorrhagic fever
- Dengue fever
- Dukes' disease
- Influenza A virus subtype H1N1
- Infectious mononucleosis
- Marburg virus
- Neisseria meningitidis
- Rocky Mountain spotted fever
- Scarlet fever
- Typhus 
- Non-infectious conditions
- Idiopathic thrombocytopenic purpura
- Celiac Disease
- Aplastic anaemia
- Childhood protein-energy malnutrition such as Kwashiorkor or Marasmus
- Erythroblastosis fetalis
- Henoch-Schönlein purpura
- Kawasaki disease
- Schamberg's disease
- Ehlers–Danlos syndrome
- Gua Sha, a Chinese treatment that scrapes the skin
- High-G training
- Hickey (injury)
- Asphyxiation (discussed below)
Causes of particular types 
Facial petechiae, especially around the eyes, indicate physical trauma such as by hard bouts of coughing, vomiting or crying.
See also 
- Purpura, which is the mid-sized type of hematoma (3mm-1cm)
- Ecchymoses, which is the large type of hematoma (>1cm)
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