Eczema herpeticum, or Kaposi varicelliform eruption, is a superficial, widespread cutaneous infection with herpes simplex virus (HSV) 1 or 2 in a patient with preexisting skin disease. The herpes infection may be primary and sustained from a close contact, or it may occur via autoinoculation. Vesicles, pustules, and characteristic "punched-out" erosions with hemorrhagic crust are superimposed on areas of preexisting skin disease. Presentation ranges from mild and transient to life-threatening.

Eczema herpeticum is more commonly seen in patients with atopic dermatitis but may also be seen in cases of Darier disease, autoimmune bullous dermatoses, burns, mycosis fungoides, pityriasis rubra pilaris, and other forms of dermatitis such as irritant contact and seborrheic dermatitis. It mostly affects children but can occur in any age group.

Risk factors that have been proposed for the development of eczema herpeticum include mutations in filaggrin and deficiency of cathelicidins, skin antimicrobial peptides, in the skin.

Patients can develop numerous vesicles that may appear in crops for several days. Associated systemic symptoms can include high fevers, lymphadenopathy, and malaise. The primary infection is usually more severe than recurrent episodes.

Complications of eczema herpeticum include secondary bacterial infection and multi-organ involvement, including keratoconjunctivitis, meningitis, and encephalitis. Commonly implicated pathogens in bacterial superinfection include Staphylococcus aureus or Streptococcus pyogenes. Systemic viremia can result in serious morbidity and mortality, especially in infants.

Eczema herpeticum is rare during the neonatal period. If HSV infection develops during the first week of life, the diagnosis of neonatal herpes simplex virus should be considered. Eczema herpeticum is a medical emergency in neonates, infants, and children, and early treatment with antiviral therapy is required.