Erythema Toxicum Neonatorum Workup

Updated: Jul 10, 2017
  • Author: Neil F Gibbs, MD; Chief Editor: William D James, MD  more...
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Laboratory Studies

Erythema toxicum neonatorum (ETN) is diagnosed clinically based on history, physical examination, and peripheral smear of intralesional contents.

On a CBC count, eosinophilia are noted in approximately 15% of patients as up to 18% of the total WBC count. Eosinophilia may be more pronounced when the eruption shows a marked pustular component.

A Wright stain performed on intralesional contents will reveal primarily eosinophils. Inflammatory cells are present, with greater than 90% eosinophils and variable numbers of neutrophils. [21, 23]


Other Tests

If clinical symptoms warrant concern for systemic disease, Giemsa stain fails to show eosinophils, and/or clinical suspicion warrants an evaluation of other diagnoses, perform viral, bacterial, and fungal cultures to exclude herpes simplex virus, varicella, pathogenic bacterial, and yeast infections.

Perform potassium hydroxide preparation to exclude candidiasis.



A skin biopsy is diagnostic but rarely is required for diagnosis.


Histologic Findings

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. [24, 25, 26]