Perform potassium hydroxide preparation to exclude candidiasis. A skin biopsy is diagnostic but rarely is required for diagnosis. Histologic examination of macules reveals mild dermal edema with a sparse predominantly perivascular inflammatory infiltrate composed primarily of eosinophils, with small numbers of neutrophils and monocytes. Papules have increased edema and inflammatory infiltrate with involvement of the superficial portion of the pilosebaceous unit. Eosinophilic invasion of the outer root sheath of the hair follicle is noted.
Pustules are subcorneal or intraepidermal and are found associated with the pilosebaceous orifice.
A variable infiltrate of eosinophils and monocytes may be seen with or without neutrophils in the surrounding dermis. Diagnosis rests on recognizing the characteristic history and physical findings in an otherwise healthy newborn. A complete history, physical examination, and Tzanck smear are required to differentiate between benign transient pustular eruptions of the newborn and life-threatening disease. ETN is a benign self-limited disorder requiring no treatment. Reassure parents regarding the benign transitory nature of the condition.