by William L. Weston, M.D.
Professor of Dermatology
University of Colorado Health Sciences Center
Erythema Multiforme is an uncommon, self-limited symmetrical skin rash with target lesions that begins abruptly and heals in 7 to 14 days.
For most people, a herpes simplex virus infection causes Erythema Multiforme, such as an infection of the lip (i.e., a cold sore). Occasionally, Erythema Multiforme is caused by a herpes simplex virus infection of the genitals. Rarely, other viruses will cause it.
Erythema Multiforme most commonly occurs in adolescents and, sometimes, in school age children.
After growing at the site of a cold sore, the herpes simplex virus will travel through the bloodstream to the skin and then grow in the skin cells. The target lesions associated with Erythema Multiforme are the body's attempt to eliminate the virus. People who are especially susceptible to the herpes simplex virus have difficulty clearing it from their skin.
The target lesion on the skin is the most common manifestation of Erythema Multiforme. Each target lesion has at least two zones of color change that resemble an archery target. The center of the target lesion always has some skin damage, such as a scab or a blister.
A herpes simplex virus infection on the lip (i.e., a cold sore) often precedes the appearance of the target lesion(s) by one to seven days. Sometimes, though, the preceding herpes simplex virus infection does not cause cold sores, and it is called a "subclinical infection." Erythema Multiforme recurs in most people, but not necessarily after each cold sore.
Most physicians diagnose Erythema Multiforme from the target lesions on the skin. However, Erythema Multiforme is frequently overdiagnosed, as large hives are often confused for it. Large hives have normal skin in the center; Erythema Multiforme has damaged skin in the center. Large hives often are accompanied by swelling of the hands and feet; but, Erythema Multiforme is not accompanied by such swelling. Large hives will clear up with antihistamines; but, Erythema Multiforme will not clear up with such treatment.
There is not an effective treatment at the time of the attack of Erythema Multiforme. If individuals experience an attack of Erythema Multiforme every three months or less, a preventative treatment with an oral antiherpes virus agent, such as Zovirax, Valvir, or Famvir, is effective.
If untreated, the target lesions on the skin will heal within two weeks. Steroid treatments may prolong an attack of Erythema Multiforme. Healing usually occurs without scarring of the skin.
Prevention of those factors that precipitate cold sores can be helpful. For example, sunscreen use is beneficial because sun exposure may activate the herpes simplex virus that causes Erythema Multiforme.
Studies are currently being conducted to examine how the body eliminates the herpes simplex virus. These studies will aid in understanding why individuals who are susceptible to the herpes simplex virus cannot effectively eliminate it despite immune responses that are normal.
About the Author
Dr. Weston is a Professor of Pediatrics and Dermatology at the University of Colorado Health Sciences Center and Chair of the Department of Dermatology. His scientific and clinical interests include Cutaneous immunology, Cutaneous virology, and Pediatric Dermatology.
Dr. Weston is the primary author of the Color Textbook of Pediatric Dermatology (Weston, Lane, Morelli; Mosby, Inc.) which is used by clinicians worldwide and is published in 4 languages.
He created the Genetic Skin Disorders clinic at the University of Colorado in 1998.
Copyright 2012 William L. Weston, M.D., All Rights Reserved