petechial rash vs purpura

2 min read 13-03-2025

Both petechiae and purpura are skin rashes characterized by pinpoint-sized bleeding under the skin. However, there are key distinctions between the two, stemming from the size and cause of the bleeding. Understanding these differences is crucial for proper diagnosis and treatment.

What is a Petechial Rash?

A petechial rash is a condition marked by the appearance of numerous tiny, reddish-purple spots on the skin. These spots, called petechiae, are less than 3 millimeters in diameter and do not blanch (turn white) when pressed. This non-blanching nature is key to differentiating petechiae from other skin conditions.

Petechiae are caused by bleeding from small capillaries (tiny blood vessels). This bleeding can result from a variety of factors, including:

Infections (viral or bacterial, such as meningitis or sepsis)
Blood clotting disorders
Certain medications (like anticoagulants)
Severe coughing or vomiting (leading to increased pressure)
Trauma (though usually larger areas of bleeding would result from more significant trauma)

When to Seek Medical Attention for a Petechial Rash

While some minor causes of petechiae might resolve on their own, it's vital to seek immediate medical attention if you or someone you know experiences a petechial rash accompanied by any of the following:

Fever
Headache
Stiff neck
Difficulty breathing
Other symptoms suggesting a serious illness

What is Purpura?

Purpura is similar to petechiae in that it involves bleeding under the skin. However, the key difference lies in the size of the spots. Purpuric lesions are larger than 3 millimeters in diameter. Like petechiae, they do not blanch when pressed.

Purpura can be further categorized based on size and appearance:

Purpura simplex: Small, flat purple spots that are usually caused by minor trauma.
Ecchymoses: Larger bruises (more than 1 centimeter) that are commonly caused by trauma.
Purpura fulminans: A rare and life-threatening condition involving widespread purpura, often with skin necrosis (tissue death).

Causes of purpura are similar to those of petechiae, but the more extensive bleeding indicates a potentially more serious underlying issue. Conditions like blood clotting disorders, autoimmune diseases, vasculitis (inflammation of blood vessels), and certain infections are more likely to cause purpura.