Eczema herpeticum is caused by herpes simplex virus (HSV) type 1 or 2. It may also be caused by coxsackievirus A16 or vaccinia virus. Disorders of the skin, such as eczema, pemphigus, burns, or other dermatoses, can become infected with HSV. Infection is thought to occur by autoinoculation from a latent infection or from contact with someone with an infection. The virus enters the skin when the skin barrier is impaired due to dermatitis or eczema. Skin-to-skin contact with a person who has cold sores or genital herpes usually triggers the infection. Patients with eczema herpeticum have been found to have a decreased amount of natural killer cell activity in atopic dermatitis, which in turn decreases their defense against HSV.

Complications of eczema herpeticum include systemic involvement affecting the lungs, liver, brain, GI tract, eyes, or adrenal glands. When it affects the eyes, conjunctivitis, blepharitis, keratitis, and uveitis can occur. Blindness can result from herpetic keratitis. These complications are more likely to occur when eczema herpeticum affects the face. Septicemia from secondary bacterial infections may lead to death. The most common secondary infections are caused by Staphylococcus aureus, Pseudomonas aeruginosa, and Peptostreptococcus.

Flu-like symptoms of fever, chills, and malaise may occur in a patient with preexisting dermatitis. Symptoms appear approximately 5 to 12 days after exposure. The skin may initially have clusters of umbilicated vesiculopustules that spread over 7 to 10 days. The vesicles then progress to painful, hemorrhagic, crusted, punched-out erosions that may coalesce to become large, bleeding, denuded, and infected with secondary bacteria. Affected areas include the area of dermatitis, especially in the upper body (particularly the head and neck). The patient may also have lymphadenopathy. There may be a history of contact with someone else with HSV, or the patient may have a history of primary or recurrent herpes. The illness lasts approximately 16 days, with healing occurring in 2 to 6 weeks.