The differential diagnosis is difficult and includes the common causes found in patients without HIV infection such as insect bite reactions, scabies, dermatitis herpetiformis, drug reactions, atopic dermatitis and bacterial folliculitis. Differential diagnoses and their management are listed in Table 4.

Skin biopsies from EF lesions display a folliculocentric predominance of eosinophils and lymphocytes, with frequently associated lysis of the sebaceous gland. In contrast, PPE lesions show a wedge-shaped mild-to-moderate perivascular and interstitial infiltrate of lymphocytes and eosinophils, similar to the microscopic findings of arthropod bites or stings. This, together with eosinophilia and elevated IgE levels, has led to the suggestion that PPE can be the result of an exaggerated immunological reaction to arthropod bites or stings.[166][167]