What is inflammation?

Runner with knee pain, conceptual computer illustration.
(Image credit: Getty Images)

Inflammation is a vital part of the immune system's response to physical trauma, infection or toxins. Inflammation is the body's way of healing and repairing damaged tissue and defending itself against foreign invaders, such as viruses and bacteria

Without inflammation, wounds would fester and infections could become deadly. 

There are two main types of inflammation: acute and chronic. Acute inflammation is an immediate response that is usually helpful and ideally disappears once the attack is over. However, if the inflammation does not resolve it can become chronic and problematic. Chronic inflammation has been linked to certain diseases, such as heart disease or stroke, and also plays a role in some autoimmune disorders, such as rheumatoid arthritis and lupus

Types of inflammation

Acute inflammation

Acute inflammation is the body's first line of defence. It's a short-term response with localized effects, meaning it works at the precise place where an attack begins. Galen, the second-century physician to Roman Emperor Marcus Aurelius, identified five main signs of acute inflammation:

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

In the case of acute inflammation, blood vessels dilate, blood flow increases and white blood cells swarm the injured area to promote healing, Dr. Scott Walker, a family practice doctor at Gunnison Valley Hospital in Utah told Live Science. This response is what causes the injured area to turn red and become swollen. 

Damaged or infected tissue also releases cytokines, or chemical "emergency signals" that bring in your body's immune cells, hormones and nutrients to fix the problem, Walker told Live Science.

In addition, pro-inflammatory compounds called prostaglandins create blood clots to heal damaged tissue and trigger pain. They also cause fever, which can help kill pathogens. As the body heals, the acute inflammation gradually subsides. Acute inflammation, when well-regulated by the body, typically lasts around 10 days from the initial attack. 

Dr. Scott Walker, family medicine doctor
Dr. Scott Walker

Dr. Scott Walker is a family practice doctor. He received his medical degree from the University of Utah and his Doctor of Osteopathic Medicine from Kansas City University. He completed his family medicine residency at University of Wyoming with a specialty in obstetrics. Walker is certified by the American Board of Family Medicine and the American Osteopathic Association. 

Chronic inflammation

Chronic inflammation occurs when this acute process doesn't subside completely. Chronic inflammation is also called persistent, low-grade inflammation because it produces a steady, low-level of inflammation throughout the body, as judged by a small rise in immune system markers found in blood or tissue. This type of systemic inflammation can linger for months or years, and can contribute to the development of disease.

Low levels of inflammation can be triggered by a perceived internal threat, even when there isn't a disease to fight or an injury to heal, and sometimes this signals the immune system to respond. As a result, white blood cells swarm to a particular area of the body but have nothing to do and nowhere to go, and they may eventually start attacking internal organs or other healthy tissues and cells, Walker said. In this way, inflammation can sometimes lead to autoimmune conditions.

Chronic inflammation caused by allergies, smoking or excessive alcohol consumption may also continually simmer under the surface. And while this low-grade level of chronic inflammation often does not have symptoms, doctors can test for C-reactive protein (CRP) — a marker for inflammation in the blood. For instance, high levels of CRP have been linked with an increased risk of heart disease

Besides looking for clues in the blood, a person's diet, lifestyle habits and environmental exposures can contribute to chronic inflammation. Therefore, it's important to maintain a healthy lifestyle to keep inflammation in check.

Disease caused by inflammation

Researchers are still working to understand the effects of chronic inflammation on the body and the mechanisms involved, however it's known to play a role in the development of many diseases.

Heart disease and stroke  

One theory suggests that when inflammatory cells linger in blood vessels, they promote the buildup of plaque. The body perceives this plaque as a foreign substance that doesn't belong, so it tries to wall off the plaque from the blood flowing inside the arteries. If plaques become unstable and burst, that can lead to blood clots that block blood flow to the heart or brain, leading to a heart attack or stroke.


Cancer is another disease linked with chronic inflammation. Over time, chronic inflammation can cause DNA damage and leads to some forms of cancer. For example, people with chronic inflammatory bowel diseases, such as Crohn's disease, have an increased risk of colorectal cancer.

Anti-inflammatory drugs

Most chronic inflammatory disorders have no cure, however, there are a wide range of prescription and over-the-counter drugs that can help alleviate the symptoms of inflammation. The most common over-the-counter medications are non-steroidal anti-inflammatory drugs (NSAIDs) which include:

NSAIDs work by blocking an enzyme called cyclooxygenase, which produces prostaglandins. Other drugs, such as paracetamol or acetaminophen, relieve pain but do not target inflammation. 

Corticosteroids, such as cortisone and prednisone, broadly tune down the immune response and may be prescribed for inflammatory conditions, such as asthma and rheumatoid arthritis. In asthma, for example, they can help reduce inflammation and swelling in the airways. However, although corticosteroids are effective drugs, they can have unwanted side effects, such as high blood pressure, mood swings and weight gain. 

Before taking any of these drugs, it’s always best to speak to a healthcare provider. 

Additional resources:

This article is for informational purposes only and is not meant to offer medical advice. 

Live Science Contributor

Jessie Szalay is a contributing writer to FSR Magazine. Prior to writing for Live Science, she was an editor at Living Social. She holds an MFA in nonfiction writing from George Mason University and a bachelor's degree in sociology from Kenyon College. 

With contributions from