Description^[1]

Erythema toxicum neonatorum (ETN) only occurs in the newborn. It has the appearance of small, erythematous papules and vesicles. Occasionally pustules also occur. The lesions are often surrounded by areas of diffuse blotchy erythema, giving the appearance of a distinct halo. Individual lesions are quite transient and usually disappear quickly, only to be replaced by others in different parts of the body. The condition is benign, causes no symptoms and resolves spontaneously.

Pathophysiology^[1]

The condition has been known throughout the ages and was described by ancient Mesopotamian physicians. The exact cause is not known but some authorities have attributed it to an allergy because of the prominence of eosinophils within the lesions. Some recent theories include:

• An increase in the viscosity of ground-substance (the colloidal gel that is a component of connective tissue).
• A graft-versus-host reaction triggered by maternal lymphocytes in the fetus while the immune system is still relatively immature.
• An inflammatory response involving a variety of inflammatory mediators (eg aquaporins, psoriasin, nitric oxide synthases).
• An immune system reaction involving hair follicles (the condition normally occurs on hair-bearing areas and clusters of mast cells can be seen around hair follicles).^[2]

Epidemiology^[1]

Studies have shown some variation. Incidence in the USA has been reported as between 30-70% of newborns. There is considerable geographical variation with Spain reporting 25% and India 20%.

Risk factors

One study identified the following risk factors:^[3]

• Male gender.
• Term birth.
• First pregnancy birth.
• The birth season (higher in summer and autumn).
• Feeding with milk powder substitute or a mixed diet.
• The length of labour in vaginal delivery.

Presentation^[3]

The typical rash appears in newborns between the ages of 3 days to 2 weeks. Rarely, it can occur within the first 48 hours. The transience of the lesions is characteristic; they can appear or disappear within minutes to hours.

The lesions generally start on the trunk and then spread outwards to the face and extremities.

Differential diagnosis^[2][3]

• Herpes simplex virus Infection
• Impetigo
• Listeria infection
• Neonatal sepsis
• Varicella
• Milia
• Miliaria
• Folliculitis

Investigations^[1]

• The characteristic appearance of the lesions, their fleeting nature and the lack of systemic features makes the condition fairly easy to diagnose clinically.
• If the clinical picture is atypical, material taken from a pustule should be examined to exclude bacterial, viral and fungal infections.
• A peripheral blood film may show eosinophilia.
• If systemic sepsis is suspected, blood cultures should be taken to exclude Group B streptococcus, Listeria spp., Escherichia coli and other pathogens.
• If necessary, a skin biopsy should be taken. Typically, there is accumulation of primary eosinophils. Other features may be neutrophils in the follicular epithelium, hyperkeratosis, and follicular plugging.

Management^[1]

The condition is self-limiting and requires no treatment. Parents should be reassured about this but advised to report any atypical features.

Complications^[1]

No complications occur. Despite the presence of eosinophils within the lesions, no links to atopic conditions have been established.

Prognosis^[1]

Full resolution is expected within two weeks of onset. 11% of patients develop a recurrence 6 weeks later.^[2]