What Is Purpura? Understanding Symptoms, Causes, and Diagnosis

Purpura is a medical condition characterized by the appearance of purple or reddish spots on the skin caused by bleeding underneath the surface. These spots, which typically range from small dots to larger patches, do not blanch when pressed—a key distinguishing feature from other types of rashes. While purpura can occur anywhere on the body, it most commonly appears on the lower extremities, particularly the legs and feet, due to increased pressure and gravity affecting blood circulation in these areas.

Common Types of Purpura

There are several underlying causes of purpura, with the two most frequent types being allergic (or immune) purpura and thrombocytopenic purpura. Although both result in visible skin discoloration, their root causes and health implications differ significantly.

Allergic Purpura (Henoch-Schönlein Purpura)

This form of purpura is often triggered by an abnormal immune response, usually following an infection, medication, or exposure to allergens. It leads to inflammation of small blood vessels (vasculitis), increasing their permeability. As a result, red blood cells leak into surrounding tissues, causing the characteristic rash. Allergic purpura is more common in children but can also affect adults. In addition to skin symptoms, it may involve joint pain, abdominal discomfort, and kidney involvement, making early diagnosis essential.

Thrombocytopenic Purpura

Unlike allergic purpura, thrombocytopenic purpura stems from a deficiency in platelets—blood cells critical for clotting. When platelet counts drop below normal levels, even minor injuries can lead to excessive bleeding under the skin. This type is considered more serious because it reflects a dysfunction in the body's hemostatic system and may be associated with conditions such as autoimmune disorders, viral infections, certain medications, or bone marrow issues. Left untreated, it can increase the risk of severe internal bleeding.

How to Differentiate Between the Two

Distinguishing between allergic and thrombocytopenic purpura is crucial for proper treatment. A simple yet effective method involves a complete blood count (CBC) test, which measures platelet levels. If the platelet count is within the normal range, allergic purpura is more likely. Conversely, low platelet counts point toward thrombocytopenic purpura.

In addition to blood work, a urinalysis should be performed to assess potential organ involvement, especially kidney function. The presence of red blood cells, hemoglobin, or protein in the urine may indicate systemic inflammation or damage, commonly seen in Henoch-Schönlein purpura. Imaging studies or specialized antibody tests might also be recommended depending on clinical presentation.

When to Seek Medical Attention

If you notice unexplained bruising or purple spots that don't fade with pressure, especially if accompanied by fatigue, frequent nosebleeds, or joint pain, consult a healthcare provider promptly. Early evaluation helps rule out serious conditions and prevents complications such as chronic kidney disease or hemorrhage.

While mild cases of purpura may resolve on their own, accurate diagnosis ensures appropriate management—whether through antihistamines, corticosteroids, immunosuppressive drugs, or platelet-boosting therapies. Lifestyle adjustments, including avoiding known allergens and monitoring for recurrence, also play a supportive role in long-term health.