What is an inflammation?

When a wound swells up, turns red and hurts, it may be a sign of . Very generally speaking, is the body’s ’s response to an irritant. The irritant might be a germ, but it could also be a foreign object, such as a splinter in your finger.

This means that an doesn’t only start when, for instance, a wound has already been infected by , is oozing pus or healing poorly. It already starts when the body is trying to fight against the harmful irritant.

What causes an inflammation?

Many different things can cause inflammations. These are the most common:

  • Pathogens (germs) like bacteria, viruses or fungi
  • External injuries like scrapes or damage through foreign objects (for example a thorn in your finger)
  • Effects of chemicals or radiation

Diseases or medical conditions that cause often have a name ending in “-itis.” For example:

What are the signs of an inflammation?

There are five symptoms that may be signs of an acute :

  • Redness
  • Heat
  • Swelling
  • Pain
  • Loss of function

Examples of a loss of function include not being able to move an inflamed joint properly, having a worse sense of smell during a cold, or finding it more difficult to breathe when you have .

Inflammations don’t always cause all five symptoms. Some inflammations occur “silently” and don’t cause any symptoms.

What are the potential consequences of a severe inflammation?

If the is severe, it can cause general reactions in the body. These may include the following signs and symptoms:

  • Generally feeling ill, exhaustion and fever. These are signs that the is very active and needs a lot of energy, which may be lacking for other activities. If the rate of metabolism is higher due to a fever, more antibodies and cells of the can be produced.
  • Changes in the blood: The levels of substances in the blood that are taken as signs of increase, including C-reactive protein (CRP), the erythrocyte sedimentation rate (ESR), and the number of white blood cells.

In very rare cases, an can lead to a dangerous in the body that is part of an response known as sepsis. This may occur if germs multiply quickly in a certain part of the body and then a lot of them suddenly enter the bloodstream, leading to blood poisoning (septicemia). This can happen if the body isn’t able to fight the locally, if the germs are very aggressive, or if the immune system is very weak.

Important:

If you think that someone has septicemia, seek medical attention immediately The possible signs of septicemia include chills, a very high fever, and feeling extremely unwell.

What exactly does inflammation involve?

When an occurs in your body, many different cells may be involved. They release various substances, known as inflammatory mediators. These include the bradykinin and histamine. They cause the small blood vessels in the tissue to become wider (dilate), allowing more blood to reach the injured tissue. For this reason, inflamed areas turn red and feel hot.

The increased blood flow allows more cells to be carried to the injured tissue, where they help with the healing process. What’s more, both of these irritate nerves and cause pain signals to be sent to the brain. This has a protective function: If the hurts, you tend to protect the affected part of the body.

These signals also help make it easier for cells to pass out of the small blood vessels, so that more of them can enter the affected tissue. Then more fluid enters the inflamed tissue as well, which is why it often swells up. The swelling goes down again after a while, when this fluid is transported out of the tissue.

Mucous membranes also release more fluid when they are inflamed. For instance, this happens when you have a stuffy nose and the membranes lining your nose are inflamed. Then the extra fluid can help to quickly flush the viruses out of your body.

What are chronic inflammatory diseases?

Inflammations don’t always help the body. In some diseases the fights against the body’s own cells by mistake, causing harmful inflammations. These include, for example:

Collectively known as chronic inflammatory diseases, these diseases can last for years or even a lifetime. Their severity and level of activity varies.

Loscalzo J, Kasper DL, Longo DL et al. Harrison's Principles of Internal Medicine (Vol. 1 & Vol. 2). New York: McGraw-Hill; 2022.

Pschyrembel Online. 2025.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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Updated on April 11, 2025

Next planned update: 2028

Publisher:

Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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