Erythema toxicum neonatorum is a benign and frequent condition of the newborn infants. The condition is of unclear etiology, it's more often seen in term infants than in premature ones, and it's characterized by generalized skin rash, evanescent macules, papules, and pustules in an otherwise well and healthy child, that resolve with no intervention.
Erythema toxicum neonatorum usually appears after the age of 3 days and within the first two weeks of life, but they may rarely occur slightly before or later  . Manifestations consist of macular erythema, papules, pustules, and vesicles. Particular skin changes resolve by themselves in several minutes to hours, leaving no sequelae . As old lesions disappear, new ones appear and the total duration of erythema toxicum neonatorum is from five days to two weeks. The patient is not febrile during this period and signs such as lethargy or irritability are absent. Mucosal involvement is almost always absent and, when present, the physician should consider herpes simplex infection or candidiasis, especially if present in the mother . Once the disease is resolved, recurrence is infrequent but mild episodes are possible before the sixth week of life.
The skin lesions with an erythematous halo spread centripetally. They are usually absent in the palmar and plantar areas while the lesions are most often found on the face , trunk, proximal limbs, and buttocks but may even involve the genitalia . Their size is variable, they are blanchable, and have irregular margins.
Caucasian infants born after a long labor by vaginal delivery, who have a higher birth weight and are born at a higher gestational age are more likely to develop erythema toxicum neonatorum and manifestations tend to have a longer duration. Newborns that receive infant formulas, those born in the summer or autumn whose mothers are younger than 30 years are also at a higher risk .
Clinical examination and attentive history inquiry are key tools for erythema toxicum neonatorum diagnosis and further investigations are usually unnecessary. A complete blood count may reveal increased eosinophil numbers. The histological evaluation of intralesional content shows the presence of eosinophils and neutrophils  . If eosinophils are absent or a systemic disease is suspected, bacterial, viral, and fungal cultures are required. A potassium hydroxide preparation may confirm or exclude candidiasis. If cultures are proven negative and doubt still persists, a skin biopsy should be performed. In the case of erythema toxicum neonatorum, this method will highlight the presence of dermal edema and perivascular inflammatory infiltrate. The root sheath of the hair follicle may also be invaded by eosinophils while pustules are filled with the eosinophil-rich material . In a severely ill child, blood cultures are indicated in order to exclude sepsis. Herpes virus infection can also be ruled out using fluorescent antibody testing or a Tzanck preparation.