Erythema Multiforme

Erythema multiforme (EM) is a rash that occurs mostly on the skin. Sometimes it occurs on the lips and mouth. It is usually a mild illness that goes away on its own. It usually affects young adults in the spring and fall. It tends to be recurrent with each episode lasting 1 to 4 weeks.


The cause of EM may be an overreaction by the body's immune system to a trigger (something that causes the body to react).

Common triggers include:

  • Infections, including:

  • Viruses.

  • Bacteria.

  • Fungi.

  • Parasites.

  • Medicines.

Less common triggers include:

  • Foods.

  • Chemicals.

  • Injuries to the skin.

  • Pregnancy.

  • Other illnesses.

In some cases the cause may not be known.


The rash from EM shows up suddenly. The rash may appear days after the trigger. It may start as small, red, round or oval marks that become bumps or raised welts over 24 to 48 hours. These can spread and be quite large (about one inch [several centimeters]). These skin changes usually appear first on the backs of the hands, then spread to the tops of the feet, arms, elbows, knees, palms and soles. There may be a mild rash on the lips and lining of the mouth. The skin rash may show up in waves over a few days. There may be mild itching or burning of the skin at first. It may take up to 4 weeks to go away.

The rash may come back again at a later time.


Diagnosis of EM is usually made by physical exam. Sometimes a skin biopsy is done if the diagnosis is not certain. A skin biopsy is the removal of a small piece of tissue which can be examined under a microscope by a specialist (pathologist).


Most episodes of EM heal on their own and treatment may not be needed. If possible, it is best to remove the trigger or treat the infection. If your trigger is a herpes virus infection (cold sore), use sunscreen lotion and sunscreen-containing lip balm to prevent sunlight triggered outbreaks of herpes virus. Medicine for itching may be given. Medicines can be used for severe cases and to prevent repeat bouts of EM.


  • If possible, avoid known triggers.

  • If a medicine was your trigger, be sure to notify all of your caregivers. You should avoid this medicine or any like it in the future.


  • Your EM rash shows up again in the future


  • Red, swollen lips or mouth develop.

  • Burning feeling in the mouth or lips.

  • Blisters or open sores in the mouth, lips, vagina, penis or anus.

  • Eye pain, redness or drainage.

  • Blisters on the skin.

  • Difficulty breathing.

  • Difficulty swallowing; drooling.

  • Blood in urine.

  • Pain with urinating.