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Diphtheria can cause potentially life-threatening complications, such as breathing difficulties and problems with the heart and nervous system.

Diphtheria can lead to potentially life-threatening complications, such as breathing difficulties and problems with the heart and nervous system.

Respiratory failure

Diphtheria can cause serious breathing difficulties because:

  • the membrane that covers your throat can make breathing difficult
  • small particles of the membrane can fall down into your lungs, leading to widespread inflammation of the lungs

There's a risk that someone with diphtheria will lose their normal lung function. This is called respiratory failure.

If you're considered at risk of respiratory failure, a ventilator will be used to help with your breathing. The ventilator will move oxygen-enriched air in and out of your lungs while the underlying infection is treated.


The toxin that's produced by diphtheria bacteria can inflame the muscles of your heart. Inflammation of the heart muscles is known as myocarditis.

Myocarditis can cause your heart to beat irregularly, causing heart block. This is when the electrical pulses that control the beating of your heart are disrupted, causing your heart to beat very slowly (bradycardia).

The heart block can be treated with a temporary pacemaker. It can be inserted into your chest to help your heart beat regularly.

In the most serious cases of myocarditis, the heart can become so weak that it can't pump blood around your body and you will have heart failure.

Nervous system complications

Diphtheria can cause complications that affect the nervous system (neurological complications). These can occur weeks after you first experience diphtheria symptoms.

Paralysis of the diaphragm

One possible complication is your diaphragm being paralysed. The diaphragm is a thick dome-shaped muscle that separates your chest from your abdomen. It helps you breathe in and out.

If the diaphragm is not working properly, you will need a ventilator to help you breathe. This can mimic the function of your diaphragm by regulating the pressure of your lungs. Unless you are put on a ventilator immediately, paralysis of the diaphragm can be fatal.

The diaphragm can become paralysed very suddenly, over a period of around 30 minutes. It can become paralysed weeks after you first develop diphtheria, even after you have recovered from the initial infection and any other complications.

For this reason, children with diphtheria and other complications, such as those affecting the heart, may be kept in hospital for up to six weeks, even if they appear to be better.

Bladder problems

Another possible complication is problems with the nerves controlling your bladder (neurogenic bladder dysfunction). If these nerves are damaged, you won't be able to fully empty your bladder.

This can cause symptoms such as:

  • needing to urinate often
  • only passing a small amount of urine
  • losing control of your bladder

Bladder problems often develop before paralysis of the diaphragm, so this can be an early warning sign that you'll develop more serious breathing problems.

Malignant diphtheria

Malignant diphtheria, also known as hypertoxic diphtheria or diphtheria gravis, is a very severe form of diphtheria. As well as the other symptoms of diphtheria, people with malignant diphtheria develop:

  • severe bleeding problems
  • kidney failure

Malignant diphtheria is often fatal. It's likely to be caused by a particular type of Corynebacterium diphtheriae bacteria.

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