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Erythema multiforme is a skin reaction that can be triggered by an infection or medication. It's usually mild and goes away in a few weeks.
But there's also a rare, severe form that can affect the mouth, genitals and eyes and can be life-threatening. This is known as erythema multiforme major.
Erythema multiforme mainly affects adults under 40, although it can occur at any age.
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Most people with erythema multiforme will just have a rash, but other symptoms can also sometimes occur.
The rash comes on suddenly and develops over a few days. It tends to start on the hands or feet, before spreading to the limbs, upper body and face.
In more severe cases, the patches may join together to form large, red areas that may be raw and painful.
Additional symptoms of erythema multiforme can include:
These symptoms are more common in erythema multiforme major or a similar condition called Stevens-Johnson syndrome.
See your GP as soon as possible if you think you or your child may have erythema multiforme.
Your GP may be able to diagnose it just by looking at the rash, but they can refer you to a skin specialist (dermatologist) if they're not sure.
If erythema multiforme major or Stevens-Johnson syndrome is suspected, you'll be referred to hospital immediately because these conditions can be serious.
The cause of erythema multiforme is often unclear, but some cases are the result of a reaction to an infection or medication.
The condition can't be passed from person to person.
Most cases are caused by a viral infection – often the herpes simplex (cold sore) virus. This virus usually lies inactive in the body, but it can become reactivated from time to time.
Some people will get a cold sore a few days before the rash starts.
Erythema multiforme can also be triggered by mycoplasma bacteria, a type of bacteria that sometimes cause chest infections.
Medication can occasionally cause the more severe form of erythema multiforme. Possible medication triggers include:
Treatment aims to tackle the underlying cause of the condition, relieve your symptoms and stop your skin becoming infected.
Your doctor may recommend:
More severe cases may be treated in hospital with:
Most people with erythema multiforme make a full recovery within a few weeks. There aren't usually any further problems and the skin normally heals without scarring.
But there is a risk the condition could come back at some point, especially if it was caused by the herpes simplex virus.
You may be given antiviral medication to prevent attacks if you experience them frequently.
In severe cases, possible complications can include: