What is inflammation?

The body's 'Goldilocks' response can kill or cure

Person running showing stress and pain in the knee joint on knee joint

We all know inflammation when we see it – the red and painful cut, the hot, swollen thumb we’ve hit with a hammer, or the angry welt of an insect bite.

These are all outward signs of the process initiated by many systems in our body in response to danger, in the form of a physical injury, an infection, or even our own body not behaving as it should.

Inflammation is a vital short-term response to a sudden insult, whether that is injury, infection or both. Messenger proteins, known as cytokines, are released to signal the danger, and our system responds with the tools to fix the problem. 

Pain, swelling, redness and heat are the classic external signs of this process. 

The pain warns us to take care and notifies us of the insult; an area may become swollen as fluids are moved to the injury; heat and redness follow as increased blood flow brings cells to start the healing process; and hormone-like messaging systems can order the blood to clot to close a wound.

When pathogens like bacteria or viruses are present, the immune response involves dispatching white blood cells to fight off and kill the infection.

If all goes well, inflammation will subside and our bodies will return to normal as the damage is healed or the pathogen is destroyed.

But inflammation is a “Goldilocks” condition – too little and our bodies can be overwhelmed by infection or fail to heal; too much and it can cause crippling health problems of its own.

Where the immune system cannot return to normal because our body fails to heal, or environmental factors such as smoking or diet maintain a threat, inflammation goes into overdrive and can continue to signal danger.  Scientists now understand that this long-term inflammatory response, known as chronic inflammation, can lead to many chronic diseases.

So inflammation is a shapeshifter. It can be both a symptom of injury or disease, or a cause of symptoms. 

Scientists and doctors are only beginning to build a detailed understanding of the many moving parts of this complex system. As they do, they are devising strategies to control inflammation and provide new approaches to tackle many important and common diseases.

Inflammation is a shapeshifter.
It is both a symptom of injury or disease, and at the same time the cause of symptoms.

For more information on what is happening with IMB research read our story on macrophages.

How inflammation works

A complex set of steps involving many of the body’s systems

Graphic of blood cells going through vein

The inflammatory response begins when damaged tissue releases chemical signals that, among other functions, cause blood vessels to become porous.

Phagocytes – the cells which protect the body by engulfing foreign particles and bacteria – then move from the blood vessel into the affected tissue to attack bacteria and clean up debris. 

Platelets move to the wound to cause blood clotting. 

The aim is to return the tissue to the way it was before the injury.

With chronic inflammation, the process does not stop and, instead of attacking a foreign invader and protecting us from disease, the inflammation now attacks the body itself.  

Cross section of skin and body showing cells and blood vessel

Acute vs chronic

What’s the difference?

Woman sitting beside three bowls with post it notes reading "Too hot" "Too cold" and "Just right"
  • Acute inflammation is the first line of defence against injury or infection. It is usually a sign that your body has taken the first step towards healing, but this response can also be involved in illness, such as sepsis. Acute inflammation comes on quickly and lasts a matter of days, but can be fatal.
  • Chronic inflammation, by contrast, comes on slowly and can last for months or even years. It is persistent inflammation that tries to rectify a problem, such as an autoimmune disease or ongoing exposure to environmental or lifestyle irritants such as pollution or smoking. Acute inflammation, if not resolved, can turn into chronic inflammation.
  • The mechanics of the response can be similar as for an emergency, but as the injury or infection cannot be resolved, the distress signals continue. The consequences of this persistent inflammation are one or more of a raft of health conditions.
  • Inflammation becomes the problem and not the solution. 
Three bowls with post it notes reading "Too hot" "Too cold" and "Just right"


Alzheimer’s is an inflammatory disease which affects 10 per cent of people aged over 65.

Among those aged 85 or more that rises to


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