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Differences between petechiae & purpura

Updated March 23, 2017

Although bleeding under the skin, diagnosed by doctors as one of several conditions including petechiae and purpura, is a symptom of a wide-ranging number of medical disorders, it can signal the onset of a severe illness. Both conditions are caused by small amounts of bleeding just under the skin's surface, and appear as red spots, eventually fading to blue and brown similar to the way a bruise fades.

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Petachiae are tiny, pinpoint-sized blotches that usually appear in clusters similar to a rash. Most doctors consider blotches only as large as 3 or 4mm for a diagnosis. The colour in petechiae doesn't fade when pressure is applied to the skin.


Purpura are blotches similar to petechiae, only larger, with a maximum size of 1cm. As with petechiae, purpura don't fade when pressure is applied to the skin.


Any bleeding into the skin larger than 1cm is diagnosed as an ecchymosis, which is commonly referred to as a bruise. Ecchymosis usually involves blood loss at a deeper tissue level then petechiae and purpura.

Causes and Treatment

Although many possible causes exist for petechiae and purpura, both conditions may be symptomatic of greater issues, such as allergic reactions, autoimmune diseases or vitamin deficiency. Purpura may also be caused by a low blood-platelet count. Treating these skin symptoms is a matter of identifying and dealing with the underlying issue.

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About the Author

Wilhelm Schnotz has worked as a freelance writer since 1998, covering arts and entertainment, culture and financial stories for a variety of consumer publications. His work has appeared in dozens of print titles, including "TV Guide" and "The Dallas Observer." Schnotz holds a Bachelor of Arts in journalism from Colorado State University.

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