Inflammation is how the body responds when its tissues are injured by bacteria, trauma, toxins, heat, or any other cause. The damaged cells release chemicals that lead to swelling, which helps keep the foreign substance away from healthy tissues. Inflammation also attracts white blood cells that eliminate germs and dead or damaged cells.
While the word “inflammation” is sometimes used interchangeably (and mistakenly) with swelling, they’re not the same process. Instead, swelling is often a symptom of inflammation that may develop along with other signs, like pain or skin discoloration.
“Swelling is a part of inflammation, but what we perceive as swelling usually involves fluid buildup. You can have inflammation without obvious swelling, such as with early inflammatory arthritis or a nerve injury,” says Steven P. Cohen, MD, a professor of anesthesiology and the vice chair of Research and Pain Medicine at the Northwestern University Feinberg School of Medicine in Chicago, who has researched inflammation’s role in chronic pain and rheumatological disorders.
There are two broad categories of inflammation: acute and chronic.
What Is Acute Inflammation?
Acute (or short-term) inflammation happens as an immediate response to tissue damage, typically from an injury, infection, or exposure to a harmful substance.
This reaction requires coordinated engagement of your body’s inflammatory responses, says Akiko Iwasaki, PhD, a professor of immunobiology at the Yale University School of Medicine in New Haven, Connecticut. When you get an infection, for example, inflammation helps clear the pathogen and initiate immune responses, she explains. This helps the body remember the pathogen if you encounter it again, so you build up immunity.
During the acute inflammatory process, your immune system releases certain chemicals known as inflammatory mediators, including the molecules bradykinin and histamine. They help call other inflammatory mediators (signaling molecules like proteins and lipids) to the affected area to promote healing and also prompt the nerves to send pain signals to the brain to protect the area from additional damage.
Common conditions that trigger acute inflammation include the following examples:
What Is Chronic Inflammation?
Chronic inflammation is a slow, long-term inflammatory reaction that can last months or years, depending on the underlying cause.
For example, when your body fails to fight off an infection from a persistent pathogen like COVID-19, the immune system engages the inflammatory response for a long period of time, Dr. Iwasaki explains.
Chronic inflammation is also symptomatic of metabolic diseases like diabetes. Experts believe that cells in the body may overproduce chemicals that trigger inflammation.
Unlike acute inflammation — in which the inflammatory process stops when healing is complete — chronic inflammation is an ongoing overreaction as the body fails to turn off its emergency immune system response once an initial threat is gone, which can be problematic for your health. Experts believe that the immune system continues attacking as a result of inflammatory signals that don’t go away, creating a looping cycle in which the immune response continues unregulated.
“Chronic inflammation no longer serves a useful function or as a warning sign in most cases, and is associated with chronic pain, heart disease, obesity, stroke, and even psychiatric conditions such as depression and anxiety,” says Dr. Cohen.
Chronic inflammation is linked to the following conditions:
