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 inflammation often have a name ending in “-itis.” For example:

• Cystitis: an inflammation of the bladder
• Bronchitis: an inflammation of the bronchi
• Otitis media: an inflammation of the middle ear
• Dermatitis: a disease where the skin is inflamed

What are the signs of an inflammation?

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

• 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 bronchitis.

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 inflammation 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 immune system 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 immune system can be produced.
• Changes in the blood: The levels of substances in the blood that are taken as signs of inflammation increase, including C-reactive protein (CRP), the erythrocyte sedimentation rate (ESR), and the number of white blood cells.

In very rare cases, an infection can lead to a dangerous inflammation in the body that is part of an immune system 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 infection locally, if the germs are very aggressive, or if the immune system is very weak.

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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 inflammation occurs in your body, many different immune system cells may be involved. They release various substances, known as inflammatory mediators. These include the hormones 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 immune system cells to be carried to the injured tissue, where they help with the healing process. What’s more, both of these hormones irritate nerves and cause pain signals to be sent to the brain. This has a protective function: If the inflammation hurts, you tend to protect the affected part of the body.

These signals also help make it easier for immune system 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 immune system fights against the body’s own cells by mistake, causing harmful inflammations. These include, for example:

• Rheumatoid arthritis, where many joints throughout the body are permanently inflamed
• Psoriasis – a chronic skin disease
• Inflammatory bowel diseases like Crohn’s disease or ulcerative colitis

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

Sources

• 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.

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