Petechiae vs. Purpura: What Skin Discoloration Can Tell You About Your Health

Petechiae and purpura are two related symptoms that occur when tiny blood vessels called capillaries burst and leak under the skin. Petechiae are tiny, red pin spots that often develop in clusters, while purpura is a larger area of discoloration that tends to be more purplish.

Petechiae is essentially a smaller version of purpura. Both can be caused by the same conditions and treated in the same way. They are ultimately due to the loss of platelets (blood cells involved with clotting), damaged blood vessels, or clotting problems.

This article describes the symptoms and causes of petechiae and purpura, including how they are diagnosed and treated.

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Petechiae vs. Purpura: Difference in Appearance

Petechiae and purpura are both caused by the same mechanism, namely the leaking of blood from capillaries. They both cause skin discoloration and are non-blanching (meaning they don't lighten when pressed).

Where they differ is in their size, shape, texture, and color. By definition:

• Petechiae are less than 4 millimeters (mm) in diameter.
• Purpura are between 4 mm and 10 mm in size.

Areas that are larger than 10 mm are referred to as ecchymosis, also known as bruising.

Petechiae usually appear as a cluster of tiny "bloodspots" that sit flat against the skin. With purpura, one or many areas of discoloration may be irregular in shape and often raised.

The color of petechiae and purpura can also vary. This is because blood that starts out red can gradually turn purplish, brown, or yellow as the blood cells break down and are absorbed by the body.

Because petechiae are smaller, they tend to be seen as bright red spots that vanish relatively quickly. Purpura may initially be red but quickly turn purple for a longer period due to the larger volume of blood that needs to be broken down and absorbed.

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Causes of Petechiae and Purpura

There are three main causes of petechiae and purpura, categorized as:

• Thrombocytic: Caused by the destruction or loss of platelets
• Vascular: Caused by the leakage of blood through the capillary wall
• Coagulopathy: Caused by other blood clotting disorders

Thrombocytic Causes

Thrombocytes (also called platelets) are a type of blood cell that clump together whenever there is bleeding. The clot they form can help stop bleeding.

Thrombocytopenia is a potentially serious condition where platelet numbers are very low, often due to infections or diseases that destroy them.

Causes of thrombocytopenia include:

• Autoimmune disorders like rheumatoid arthritis, lupus
• Hepatitis C, HIV, cytomegalovirus, and other viral diseases
• Leukemia and other cancers
• Bacteremia (bacterial blood infection)
• Sepsis (bacteremia that triggers a severe, whole-body inflammatory reaction)
• Thrombotic thrombocytopenic purpura (a rare disorder that "uses up" platelets by causing clots throughout the body)
• Idiopathic thrombocytopenia purpura (an often spontaneous drop of platelets for unknown reasons, mainly seen in children)
• Immune thrombocytopenia (an autoimmune disorder in which the immune system destroys platelets)
• Hemolytic uremic syndrome (a rare condition involving the kidney that triggers the destruction of blood cells)
  
• Post-transfusion purpura (an abnormal immune response to a recent blood transfusion in which platelets are targeted for destruction)

Vascular Causes

Vascular causes of purpura or petechiae are those in which blood vessels are structurally damaged or compromised, causing bleeding.

Causes include:

• Physical trauma, such as severe abrasion, friction, or compression
• Weakening of capillaries due to older age or long-term sun exposure
• Vasculitis (a group of diseases that cause blood vessel inflammation)
• Amyloidosis (a disorder that causes proteins to build up in organs and blood vessels)
• Hereditary hemorrhagic telangiectasia (a genetic disorder that causes bleeding spider veins)
• Rumpel-Leede phenomenon (the rupture of capillaries due to compression of a limb)
• Scurvy (a deficiency of vitamin C that causes blood vessel fragility)

Coagulopathy

Coagulopathy refers to bleeding problems that interfere with clotting rather than those that cause the loss or destruction of platelets.

Causes include:

• Anticoagulants ("blood thinners") like aspirin, heparin, warfarin, and Plavix (clopidogrel)
• Chemotherapy and radiation therapy (both of which suppress platelet production in bone marrow)
  
• Aplastic anemia (a condition in which the body doesn't make enough blood cells, including platelets)
  
• Disseminated intravascular coagulation (a rare condition that causes blood clots in the circulatory system)
  

How Petechiae and Purpura Are Diagnosed

Purpura and petechiae are diagnosed with a physical exam. Both symptoms are relatively easy to recognize but may be mistaken for other conditions, such as stasis dermatitis (a type of eczema) and skin cancers like basal cell carcinoma.

One way to help confirm the diagnosis is to press a water glass against the lesions. If they do not blanch (turn white), it is a positive sign of petechiae or purpura.

Both also tend to develop suddenly rather than gradually. With petechiae, there will typically be multiple spots rather than a single one.

If there is any doubt as to the cause, the healthcare provider may take a tissue biopsy, This involves a device similar to a hole punch that can extract a small column of tissue for evaluation in the lab.

To narrow the possible causes of purpura or petechiae, the healthcare provider will review your medical history, family history, medication use, and other symptoms you may have.

Treatment of Petechiae and Purpura

In some cases, petechia and purpura will resolve on their own without treatment, especially when caused by a skin injury. In such cases, you may be able to speed healing and ease discomfort by applying a cold compress to the skin and drinking plenty of fluids.

In other cases, petechiae and purpura are treated by resolving the underlying condition. 

If petechiae and purpura are due to severely low platelet counts, a blood transfusion may be needed. If petechiae or purpura are caused by medications, withholding the medication may be necessary to prevent any further bleeding.

Autoimmune causes may require treatment with immunosuppressants that temper the overactive immune response. Vitamin C may be prescribed if there is evidence of scurvy, while uncommon cases of cancer will need to be seen and treated by an oncologist.

When to Call a Healthcare Provider

Petechiae or purpura may be due to simple injury, medications you are taking, or aging-related skin damage. In cases like these, there is no cause for alarm, but it may be in your interest to see your healthcare provider if the symptom is severe or persistent.

On the other hand, there are times when petechiae or purpura can be worrisome and should seen by a healthcare provider as a matter of concern. This includes:

• When petechiae or purpura develops suddenly for no known reason
• When symptoms worsen, recur, or persist despite appropriate treatment
• When petechiae or purpura cause significant bleeding through breaks in the skin
• When petechiae or purpura are accompanied by fever, malaise (a general feeling of unwellness), abnormal skin changes, or other worrisome symptoms

Summary

Petechiae and purpura are two related conditions caused by the leaking capillaries. Petechiae is characterized by blood spots under 4 millimeters that are typically red and flat. Purpura is characterized by areas of discoloration between 4 and 10 millimeters that tend to purplish and slightly raised.

Both can be caused by a wide range of conditions that either cause the destruction of platelets, interfere with blood clotting, or damage blood vessels. The diagnosis involves a physical exam and a review of your medical history. A positive sign for purpura and petechiae is a non-blanching lesion.