Eosinophils are a type of white blood cell from the bone marrow that are part of the body’s immune response. They help defend the body against certain infections, particularly from parasites and fungi, and also participate in allergic reactions. Eosinophilia is a condition with a higher-than-normal number of these cells in the blood, defined as 500 or more eosinophils per microliter. This elevation is not a disease itself but a sign that the immune system is responding to a trigger, such as an allergy or an underlying medical condition. While part of the body’s defense system, substances released by eosinophils can also cause inflammation and tissue damage.
Skin Manifestations of Eosinophilia
When eosinophils accumulate in the skin, they can cause a wide range of visible and sensory changes known as eosinophilic dermatoses. The most common symptom is intense itching, known scientifically as pruritus. This severe itching is a feature of many eosinophilic skin conditions, driven by substances released from eosinophils that stimulate nerve endings in the skin. The appearance of the skin can vary, with many individuals developing rashes that can be widespread.
Common manifestations include:
- Maculopapular rashes, which are a mix of flat, discolored spots and small, raised bumps.
- Hives (urticaria), which are raised, itchy welts that can appear and disappear.
- Fluid-filled blisters (bullae) or deeper, firm bumps known as nodules in cases of significant inflammation.
- Eczematous patterns that resemble chronic dry, scaly skin.
The specific appearance depends on the underlying trigger and which layers of the skin are most affected by the eosinophilic inflammation.
Underlying Causes
A broad range of conditions can trigger this response, with allergic reactions being among the most frequent. Conditions like atopic dermatitis (eczema) and adverse reactions to medications are common triggers for eosinophilia in the skin. In these cases, the immune system mistakenly identifies a substance as harmful, leading to the recruitment of eosinophils.
Infections are another major category of causes, particularly those involving parasites. Parasitic infections, especially by helminths (worms), provoke a strong eosinophilic response as the body attempts to eliminate the invaders. Fungal and certain viral infections can also be associated with increased eosinophil levels.
Autoimmune disorders represent another group of conditions that can lead to eosinophilic skin inflammation. In diseases like bullous pemphigoid, the immune system attacks proteins that connect layers of the skin, causing large, tense blisters and attracting a significant number of eosinophils to the site.
In some instances, the high eosinophil count is the central feature of the disorder. Conditions such as Eosinophilic Cellulitis (Wells’ syndrome) involve widespread eosinophil infiltration in the skin, mimicking a bacterial infection. A more systemic condition is Hypereosinophilic Syndrome (HES), where persistently high levels of eosinophils can lead to inflammation and damage in various organs, including the skin.
Diagnostic Process
Diagnosis begins with a physical examination of the skin and a detailed discussion of the patient’s medical history. The provider will ask about symptoms, potential exposures to new medications or foods, recent travel, and any personal or family history of allergies or autoimmune diseases to help narrow down potential triggers.
To confirm high eosinophil levels, a blood test is a primary diagnostic tool. A complete blood count (CBC) with a differential analyzes the different types of white blood cells and will show if the number of eosinophils is elevated, confirming systemic eosinophilia. The degree of elevation can also provide clues about the underlying cause.
A skin biopsy is often necessary to confirm the presence of eosinophils within the skin tissue. During a biopsy, a small sample of the affected skin is removed for microscopic examination. A pathologist will look for the accumulation of eosinophils in the skin layers, which helps link the skin condition to eosinophilic inflammation. This examination may also reveal features like “flame figures,” areas of collagen damage caused by substances released from eosinophils.
Once eosinophilia is confirmed in both the blood and skin, further investigation may be required to pinpoint the specific cause. Depending on the suspected trigger, doctors may order additional tests like allergy testing, stool sample analysis for parasites, or specialized blood tests for autoimmune conditions.
Treatment Approaches
Managing eosinophilic skin conditions is tailored to the severity of symptoms and the underlying cause. The most effective long-term approach is to identify and address the root cause. For instance, if a medication is the trigger, discontinuing the drug often leads to resolution. Similarly, treating a diagnosed parasitic infection will clear the infection and lower the eosinophil count.
For direct management of skin symptoms, treatments focus on reducing inflammation and controlling the itch. Topical corticosteroids are frequently prescribed to be applied to affected skin areas. These creams and ointments work by suppressing the local immune response, thereby reducing redness, swelling, and rash. Oral antihistamines are commonly used to combat the pervasive itching.
In more severe or persistent cases, systemic therapies that affect the entire body may be necessary. Oral corticosteroids are effective at reducing eosinophil levels and can bring severe skin inflammation under control. For certain chronic disorders like Hypereosinophilic Syndrome, newer biologic medications are an option. These therapies target specific molecules involved in the eosinophilic pathway, such as interleukin-5 (IL-5), which stimulates eosinophil production.