This patient has eosinophilic pustular folliculitis, a rash most commonly seen in patients with HIV infection, and usually in those with a CD4 cell count less than 300/µL. The lesions are typically intensely pruritic papules (and rarely pustules) clustered on the chest and face, generally in areas with a high concentration of sebaceous glands. Biopsy will reveal an eosinophilic infiltrate in the hair follicle, and peripheral eosinophilia may develop in up to 50% of patients. The exact etiology is unknown, but the condition is relatively common. Diagnosis is usually based on the presence of the typical skin rash in an appropriate clinical context. The rash usually responds to antiretroviral therapy, although high-potency glucocorticoids and systemic antihistamines may be used for symptomatic treatment.

Acne is characterized by comedonal lesions (plugged pores, blackheads) and, when drug induced, often involves the shoulders and back; this patient is not taking any drugs typically associated with drug-induced acne (glucocorticoids, bromides, lithium, certain oncologic agents [particularly epidermal growth factor-receptor antagonists], and more).

Drug reaction with eosinophilia and systemic symptoms (DRESS), also referred to as drug-induced hypersensitivity syndrome, would appear within 2 to 8 weeks of starting a new drug and would include fevers, a widespread morbilliform eruption often involving the face accompanied by facial edema, complete blood count abnormalities (eosinophilia or atypical lymphocytosis), and systemic inflammation (generally lymphadenopathy and hepatitis, although nephritis, pneumonitis, and myocarditis can occur). This patient lacks the fever and systemic symptoms of DRESS, and the rash would be atypical for this diagnosis.

Scabies can also cause intense pruritus and eosinophilia. However, patients rarely have lesions above the neck and generally have involvement of the finger web spaces, umbilicus, and, in men, the genitals.