Erythema toxicum neonatorum, aka Toxic Erythema of the Newborn

Erythema toxicum neonatorum presents as barely elevated 1-4 mm yellowish papules or pustules with a surrounding irregular, blotchy, erythematous macular flare or wheal measuring 1-3 cm in diameter. The irregular shape of the wheal has been likened to a flea bite. The characteristic lesions are discrete and scattered appearing initially on the face and then spreading to the trunk and extremities. Lesions can be found anywhere except for the palms and soles. It is a very common benign eruption that is seen in 41% to 72% of term infants. This is less common in premature infants, and rarely seen in infants less than 2500 g. The lesions usually begin during 24 to 48 hours of life and persist for about 4 to 5 days. New lesions may occur from birth up to 10 days of life. No therapy is necessary and reassurance should be provided for the parents.

Laboratory features

Usually the diagnosis is made clinically, however if there is any doubt you can scrape the pustule and smear the contents onto a glass slide. Staining with Giemsa or Wright stain will reveal sheets of eosinophils with a few scattered neutrophils under the microscope.

Differential diagnosis

Erythema toxicum can be confused with miliaria rubra, however the erythema in miliaria rubra is smaller (1 to 2 mm vs. 1 to 2 cm). It can also mimic herpes simplex or bacterial folliculitis, however a Tzanck or Gram stain will be negative. Transient pustular melanosis will usually show a predominance of neutrophils rather than eosinophils. Congenital candidiasis is more scaly and has a positive KOH.

Pathophysiology

Erythema toxicum is hypothesized to be associated with obstruction of the pilosebaceous orifice. Histologically, the lesions are intrafollicular eosinophilic pustules occurring subcorneally above the entry of the sebaceous duct. This explains the absence of lesions in the palms and soles.