Erythema multiforme is an immune-mediated skin reaction that produces distinctive “target lesions,” round spots with concentric rings of color that look like a bullseye. It ranges from a mild, self-limiting rash to a more serious condition involving the mouth, eyes, or genitals. Most episodes clear up within a few weeks, but the condition can recur, especially when triggered by the herpes simplex virus.
What Target Lesions Look Like
The hallmark of erythema multiforme is a round, well-bordered lesion with three distinct zones. The outer ring is red, sometimes with tiny blisters. The middle ring is raised and slightly swollen. The center is red and often topped by a blister. These lesions tend to appear symmetrically on both sides of the body, favoring the backs of the hands, tops of the feet, elbows, and knees. They can also show up on the palms, soles, and face.
Not every lesion looks like a perfect bullseye. Some spots start as flat red patches or raised bumps that evolve over a day or two into the classic three-zone target. You might also see “atypical” targets with only two zones or less distinct borders. The rash usually appears in crops over several days, so you can have newer, less formed lesions alongside fully developed targets at the same time.
What Causes It
Erythema multiforme is not an infection itself. It’s an overreaction of the immune system, where certain white blood cells attack the skin in response to a trigger. The most common trigger, by a wide margin, is herpes simplex virus (HSV). Up to 70% of cases are preceded by a herpes outbreak, whether a cold sore on the lip (HSV-1, responsible for about two-thirds of herpes-related cases) or a genital herpes episode (HSV-2, roughly 28% of cases). The skin reaction typically appears one to three weeks after the herpes sore.
Other infections can also set it off, including Mycoplasma pneumoniae, a common cause of “walking pneumonia” in younger people. Medications are another recognized trigger. The drugs most frequently implicated are NSAIDs (like ibuprofen), certain antibiotics, and anticonvulsants. Drug-triggered erythema multiforme is less common than infection-triggered cases, but it’s an important distinction because identifying and stopping the medication is key to recovery.
Minor vs. Major Forms
Erythema multiforme minor is the more common and milder form. It involves the skin only, or at most causes very mild irritation of the lips or inside the mouth. There’s no fever, joint pain, or general feeling of illness. Most cases fall into this category.
Erythema multiforme major involves significant inflammation of at least one mucous membrane, typically the mouth, but sometimes the eyes, nose, or genital area. Mouth involvement can be painful enough to make eating and drinking difficult. This form may also come with systemic symptoms like fever and joint aches. Some clinicians now prefer to simply classify cases as “severe” or “nonsevere” based on how prominently the mucous membranes are affected, since that’s what drives treatment decisions and day-to-day discomfort.
How It Differs From Stevens-Johnson Syndrome
Erythema multiforme major and Stevens-Johnson syndrome (SJS) can look similar at first glance, since both involve skin lesions and mucous membrane problems. But they are considered separate conditions with different causes and different levels of danger. One clear clinical differentiator is how much skin peels or blisters off. In erythema multiforme major, skin peeling is limited to about 1 to 2% of the body’s surface area. In SJS, the peeling covers up to 10% of the body, and in the most severe form (toxic epidermal necrolysis), it exceeds 30%.
Erythema multiforme also tends to favor the extremities, while SJS typically starts on the trunk and face. And while erythema multiforme is most often triggered by infections, SJS is more commonly a drug reaction. This distinction matters because SJS is a medical emergency requiring hospital care, whereas most erythema multiforme episodes resolve on their own.
How It’s Diagnosed
Diagnosis is primarily visual. A doctor familiar with the condition can often identify it from the appearance and distribution of the target lesions alone. Your history matters too: a recent cold sore, a new medication, or a respiratory infection in the weeks before the rash all point toward erythema multiforme.
When the diagnosis is uncertain, a small skin biopsy can confirm it. Under a microscope, the tissue shows a pattern of immune cells infiltrating the skin and causing damage to the outermost layer. This helps rule out other conditions that produce similar-looking rashes, such as hives (urticaria), lupus-related skin disease, or vasculitis.
Treatment and Recovery
Mild erythema multiforme often doesn’t need specific treatment beyond symptom relief. Cool compresses, antihistamines for itching, and over-the-counter pain relievers can help you get through the episode. The rash typically resolves within two to four weeks without scarring, though some temporary discoloration of the skin may linger for a few months.
For erythema multiforme major with painful mouth or genital sores, treatment focuses on managing pain and preventing complications like dehydration from not eating or drinking. Topical numbing agents for mouth sores and anti-inflammatory mouthwashes can provide relief. In more severe cases, a short course of systemic corticosteroids may be used, though their role remains debated among dermatologists.
If a medication triggered the reaction, stopping that drug is the most important step. You’ll want to make sure every healthcare provider you see knows about the reaction so the drug (and related drugs in the same class) can be avoided in the future.
Preventing Recurrent Episodes
Erythema multiforme recurs in a significant number of people, particularly those whose episodes are triggered by herpes simplex. If you experience multiple flares per year, daily antiviral suppressive therapy can break the cycle. Standard regimens include low-dose antiviral medication taken twice daily, often continued for six months to a year or longer depending on how frequently episodes were occurring.
These antivirals work by keeping the herpes virus from reactivating, which removes the trigger for the immune overreaction in the skin. For people with frequent recurrences, suppressive therapy can dramatically reduce or eliminate episodes. If outbreaks return after stopping the antiviral, the medication can be restarted for another course.
For people whose erythema multiforme isn’t linked to herpes, prevention focuses on avoiding known triggers. That means steering clear of implicated medications and, where possible, reducing exposure to other infectious triggers through good hygiene and prompt treatment of respiratory infections.