What is an inflammation?

When a wound swells up, turns red and hurts, it may be a sign of inflammation. Inflammation is – very generally speaking – the body’s immune system’s response to stimulus. This can be bacteria colonizing a wound or a splinter piercing your finger, for example. Inflammation happens when the immune system fights against something that may turn out to be harmful.

Causes of an inflammation

Inflammation may have many different causes. These are the most common:

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

Diseases or 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, a middle ear infection
• Dermatitis, a disease where the skin is inflamed

Signs of an inflammation

There are 5 signs that may indicate a local acute inflammation:

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

There is a loss of function, for example, when the inflamed limb can no longer be moved properly or when the sense of smell is worse during a cold, or when it is more difficult to breathe when you have bronchitis.

This means that an inflammation does not start when a wound has been infected by bacteria, festers, or heals poorly, but already as the body is trying to fight against the harmful stimulus or a viral infection. This might lead to some confusion, because the term “inflammation” is often used differently in everyday language.

Not all 5 signs occur in every inflammation. Some inflammations occur “silently” and do not cause any symptoms. For example, women who have been infected by the human papillomavirus (HPV or HP viruses) often experience no symptoms. These viruses are transmitted by sexual contact and are very widespread. They play an important role in the development of cervical cancer. Yet HP viruses are almost always harmless because the immune system usually successfully fights them and takes care of them. You can read more about this here.

The body’s general response

Starting at a certain severity of inflammation, the body also produces general reactions in addition to the signs of inflammation in the tissue. These may include:

• General symptoms of feeling sick, exhaustion and fever: Because the rate of metabolism is higher, more defense substances and cells can be produced quickly. The body then lacks this energy in general. Increased metabolic activity can also cause fever.
• Changes in the blood such as an increased number of defense cells.

A very rare but dangerous complication is sepsis, where the infection spreads throughout the entire body through the bloodstream. This can happen if the body does not succeed in fighting the inflammation locally, the pathogens are very aggressive, or the immune system is severely weakened. Sepsis can also happen if a larger amount of germs enter the bloodstream directly, for example in an infected venous catheter. Chills, feeling very sick, and very high fever can also be signs of blood poisoning. If blood poisoning is suspected, medical assistance is urgently needed.

What happens when you have an inflammation

An inflammation is a very complex process. The body releases different substances, the inflammatory mediators. These include the tissue hormones bradykinin and histamine. They cause the narrow blood vessels in the tissue to expand, allowing more blood to reach the injured tissue. For this reason the inflamed area turns red and becomes hot. More defense cells are also brought along with the blood to the injured tissue, to help with the healing process. Both hormones also cause pain signals to be sent to the brain, so that our attention is directed to the inflammation.

The inflammatory mediators have yet another function: they increase the permeability of the narrow vessels, so that more defense cells can enter the affected tissue. The defense cells are partially transported by the blood plasma – the fluid in which the blood cells are found. The blood plasma flows from the bloodstream into the inflamed tissue. This is why inflamed tissue often swells up. This fluid is usually transported out of the tissue by the body once again some time later.

The mucous membranes also release more fluid during inflammation. This happens for example when you have a stuffy nose and the nasal mucous membranes are inflamed. Then the nasal secretions can help to quickly flush the viruses out of the body.

If inflammations do not heal completely, they can last for a longer time, or even return again and again. For example, a middle ear infection can sometimes last several months.

Inflammatory responses can also be the cause of chronic diseases

An inflammation is not always a helpful response of the body. In certain diseases the immune system fights against its own cells by mistake, causing harmful inflammatory responses. These include, for example:

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

These diseases are called chronic inflammatory diseases, and can last for years or even a lifetime in varying degrees of severity and activity.


Author: German Institute for Quality and Efficiency in Health Care (IQWiG)

© IQWiG (Institute for Quality and Efficiency in Health Care) Last update of this website: 05/22/2012