Erythema multiforme is a skin reaction (usually mild) caused by an allergy or infection. The rash tends to flare up and go away on its own, but you may need treatment for some of the symptoms.

The skin disorder gets its name from the appearance of the rash:

• erythema = redness
• multi = of many
• forme = shapes 

Most people with erythema multiforme (EM) just have a few spots that clear up quickly, but there is also a rare and more severe form that can affect the mouth, genitals and surface of the eyes, and can be life-threatening.

Who is affected?

Erythema multiforme is usually seen in children and young adults (aged 20-40), especially males. It does not appear to run in families.

What are the symptoms?

Symptoms of EM depend on the type of disease you have.

Erythema multiforme minor (mild)

If you have the mild form of EM, you may feel perfectly well but just have an uncomfortable rash. It’s usually caused by the herpes simplex virus or a bacterial infection (see What triggers it? below).

The spotty rash looks a bit like hives and usually erupts over 24 hours, starting on the hands and feet and spreading to the limbs, upper body and face. It may cause a mild burning or itching feeling.

The spots are small raised areas, some of which then develop into “bulls-eye” or “target lesions” measuring about 1-3cm across – these have a dark red centre with a blister or crust, surrounded by a paler pink ring with a bright red outermost ring.

The rash usually fades over two to four weeks, but can return.

Erythema multiforme major (severe)

This rare form of the disease is much more severe and sometimes life-threatening. It’s usually caused by a reaction to medication rather than an infection.

The rash is made up of bigger spots that may fuse to produce large red areas. They may blister to reveal raw, painful sores. You might also have:

• a fever and headache and feel unwell
• bloodshot or dry eyes that may burn, itch and weep (read more about herpes simplex eye infections)
• sensitivity to light and blurred vision
• raw sores inside your mouth, making it hard to eat and drink
• swollen lips covered in crusts
• itchy skin
• joint aches

What triggers it? 

Infection

Most cases of EM, especially EM minor, are caused by a viral infection – usually the herpes simplex (cold sore) virus. The cold sore virus lies dormant and tends to be reactivated by certain triggers. This explains why EM can flare up repeatedly.

Children with EM will usually develop a cold sore a few days before the rash starts.

The second most common trigger is a chest infection caused by mycoplasma bacteria.

Medication

Medication can sometimes trigger the more severe type of EM. Medicines that can cause EM include:

• penicillin antibiotics such as amoxicillin and ampicillin
• anticonvulsants (used to treat epilepsy) such as phenytoin and barbiturates
• sulphonamides
• tetracyclines
• non-steroidal anti-inflammatory drugs (NSAIDs) 

Experts believe that an EM reaction involves damage to the tissues and blood vessels of the skin.  

What to do

If you think you have EM, see your GP immediately. Your GP may be able to diagnose EM just by looking at your skin.

If your GP is uncertain of the diagnosis, you’ll be referred to a skin specialist (dermatologist).

How is it treated?

Treatment aims to control the illness that is causing the EM, prevent infection and manage the symptoms.

Your doctor may advise you to stop taking medication that may be triggering the EM. Don’t stop any medication without speaking to your GP first.

Symptoms can be treated with:

• antihistamines to control the itching
• moist compresses held to the skin
• antiviral tablets if the cause is a herpes simplex infection
• anaesthetic mouthwash to ease the discomfort of mouth sores
• steroid cream for inflamed skin
• painkillers for skin or mouth pain

If you have severe EM, you may need to stay in hospital and be treated in an intensive care unit or a burns unit.

You may also need:

• strong painkillers for the raw areas 
• a mouthwash that contains an anaesthetic to temporarily numb the mouth and make eating easier
• a liquid diet if the mouth is badly affected
• a short course of corticosteroid tablets to control the inflammation
• antibiotics to protect against infection of the raw skin
• eye drops or eye ointment 

Possible complications

Possible complications of EM include:

• blood poisoning 
• loss of body fluids and septic shock (where blood pressure drops to a dangerously low level)
• permanent skin damage and scarring
• skin infection (cellulitis)
• permanent eye damage

Occasionally, internal organs may be affected, causing inflammation of the heart (myocarditis), lungs (pneumonia), kidneys (nephritis) or liver (hepatitis).

Outlook

Mild cases of EM usually get better in two to three weeks using simple lotions or steroid cream, but the disease can return (usually when the cause is the herpes simplex virus). If this is the case, you may be prescribed a small daily dose of a drug to suppress the herpes simplex virus for several months.

More severe cases may take up to six weeks to get better. A few people are left with scars on their skin after the rash clears up and damaged vision if their eyes have been effected.