science of us

What Is Inflammation, and Why Is Everyone Talking About It?

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New studies on inflammation seem to come out daily. Google searches for inflammation are up 300 percent over the past 15 years. But what is inflammation, really? I usually nod along or repeat what I’ve heard without actually knowing what I’m talking about. I asked my friends for their own definitions. “Inflammation is when something makes your body kind of angry and unsettled,” one friend said. Another: “Inflammation is when your blood isn’t flowing enough, and you get puffy because it gets all backed up?” Another: “I’m picturing, like, a drawing of a human where all the organs are enlarged, red, and blinking, like in an old commercial. It’s a condition of your body being on high alert and not relaxed? I have no idea!” Also: “Inflammation is a mysterious and vague immune response that is entirely internal, unseen, unable to be tested, and the cause of all human problems?” Hmm, they all sound right to me.

I was curious, too, obviously, so I dug around, attempting to answer some questions. Here’s a little of what we know about inflammation, and a few things that are still a mystery.

What is inflammation?
Inflammation is a broad term, but essentially it’s the immune system’s response to an irritant. As a process, inflammation exists to protect the body from invasion, infection, damage, and death. A foreign body enters (via a cut, an orifice, or another entry point) or an unwanted situation arises (like a twisted knee), and our own bodies initiate the inflammation protocol to get it out, quarantine its damage, clean up the mess it’s made, take care of the injured area, and speed up healing. Without our bodies’ inflammatory response, we would all probably have died of injuries and infections by now.

So what are the symptoms? How do I know if I’m experiencing inflammation?
The traditional symptoms are redness, swelling, heat, pain, sensitivity, and impaired function (imagine a sprained ankle, a splinter, a sore throat, or a bee sting).

On a cellular level, what’s happening when something is inflamed?
When something unwelcome is introduced to the body, the immune system initiates an inflammatory response: The body releases hormones, which cause tiny blood vessels to expand around the source of the affected area, shuttling more blood, fluid, and proteins toward it, to contain and heal the damage. This is when the site of an inflammation becomes hot, red, and swollen, as in a sore throat or twisted ankle. After this comes the “termination and repair” phase, in which the offending irritant has been eliminated or destroyed and the affected tissue begins to repair itself. The cells may then regenerate, or if this is impossible, scar tissue may form instead.

So inflammation is good?
Yes, often. When the body swells up in response to a splinter, a twisted ankle, or a cold, for example, inflammation is essential for dealing with the offending irritant or situation, protecting the surrounding tissue, and then healing and regenerating the damaged tissue.

When is inflammation bad?
Well, it’s rarely comfortable, but inflammation is often worse when it doesn’t clear up or heal — or, when it becomes “chronic.” Inflammation has generally been sorted into two categories: acute and chronic.

Acute inflammation is short-lived (hours or days). Common acute irritants are germs, such as bacteria and viruses (like a cold), but also objects and injuries, such as scrapes, sprains, insect stings, and splinters. Anything that your body doesn’t want in it, or that it wants to fix, can result in acute inflammation.

Chronic inflammation is longer lasting (months or years). It’s often associated with failure to get rid of what was initially an acute irritant (like a lingering infection), long-term exposure to irritants (like polluted air), and autoimmune disorders (like lupus, Crohn’s disease, and rheumatoid arthritis).

Conditions that end in “-itis” are also inflammatory disorders: Dermatitis is inflammation of the skin, bronchitis is inflammation of the bronchi, and colitis is inflammation of the colon. Also: tonsillitis, cystitis, sinusitis, appendicitis …

How bad is chronic inflammation? That’s the one I’ve mostly been hearing about.
Chronic inflammation has now been associated with most chronic disorders and diseases — among them diabetes, cancer, heart disease, stroke, respiratory disease, arthritis, and Alzheimer’s. Inflammation may also play a role in depression. In 2006, Harvard Medical School floated inflammation as a “unifying theory of disease.”

What are the symptoms of chronic inflammation?
They’re less clear, although some potential symptoms of chronic inflammation include obesity (specifically belly fat and waist circumference) and perpetual fatigue, depression, gum disease, digestive problems (like constipation, diarrhea, and acid reflux), rashes, and body pain.

What about inflammation that doesn’t come from an external irritant? Like with autoimmune diseases?
Sometimes the body determines that parts of itself are foreign irritants, which can leave these or other parts of the body in a state of long-term or permanent inflammation. These conditions are called autoimmune (immunity against the self) disorders. In these conditions, the body produces inflammation even when there is no known foreign irritant. Some common autoimmune diseases include rheumatoid arthritis, in which joints throughout the body become permanently inflamed; psoriasis, in which the skin is chronically inflamed; and inflammatory bowel diseases, like Crohn’s disease and ulcerative colitis.

Why does it seem like everyone is talking about inflammation these days?
Primarily because scientists and researchers have been discovering a lot more about inflammation in the past several years. For instance, inflammation in the mouth and gums is associated with heart attack and stroke, inflammation in midlife can be associated with Alzheimer’s disease and memory problems later in life, and inflammation may be linked to depression (and there’s an inflammation-related link between depression and heart disease, too — and another one between depression, inflammation, and acne). Also, chronic inflammation may be associated with perpetual stress and regulation of the stress hormone cortisol.

On the other hand, because inflammation can be hard to see or quantify (at first, at least), it can make the concept a convenient and medical-sounding scapegoat/fear-mongering marketing tactic. As obstetrician-gynecologist and pain doctor Jen Gunter wrote last year in the New York Times, “The wellness industry takes medical terminology, such as ‘inflammation’ or ‘free radicals,’ and levigates it to the point of incomprehension.”

Wait, so I could have inflammation and not know it?
Well, yes, it seems … This is one of the main reasons inflammation, as a concept, has become so ubiquitous and confusing in the past 20 years or so — this increasing awareness that nebulous, sometimes seemingly symptom-less inflammation could be, or is, a common root cause of diseases (again, like cancer, diabetes, heart disease, and dementia).

Is there a way to know for sure if I’m experiencing inflammation? Are there not tests??
For people who are concerned about inflammation, and/or who are at elevated risk of heart attack, there’s something called a C-reactive protein test (or a CRP test), which is a blood test that measures levels of a blood-plasma protein that can rise with (and signal) inflammation. A CRP test can indicate the general presence of infection or a chronic inflammatory disease, such as rheumatoid arthritis or systemic lupus. High levels of CRP are associated with a higher risk of heart attack.

Other biomarkers that can indicate inflammation include high levels of certain interleukins (which are inflammation-related types of white blood cell proteins). Low levels of albumin (a substance found in blood plasma) could also indicate inflammation. These biomarkers can also be tested in a lab.

How can I prevent chronic inflammation?
No one is sure exactly what causes chronic inflammation (on a person-to-person basis), although obesity, smoking, excessive alcohol intake, and sedentary lifestyles are all associated with inflammation. So are certain genes and environmental causes (like air pollution).

Eating well can help prevent inflammation. Exercise can help prevent it, too, in an almost inoculative kind of way. Well, that might be a stretch, but I liked the way this Johns Hopkins Health Review writer put it: “Exercising, which causes an acute inflammatory response in the short term, but an anti-inflammatory one when we regularly get moving, is another strong step to take.” This is essentially the concept of hormesis, which is the idea that a small dose of something stressful in the present can result in increased resistance to the same thing later on.

Other inflammation-lowering activities: sleeping and otherwise relaxing/lowering stress. On a smaller scale, taking care of your teeth and gums is important (brush, avoid sugar), and many doctors recommend avoiding mercury-heavy fish (like swordfish), since mercury exposure is also correlated with inflammation.

What other foods cause inflammation?
Different foods do different things to different people, but generally agreed-upon foods that can cause or contribute to inflammation include refined carbohydrates, fried foods, and sugar-sweetened beverages (like soda). Sugar causes the body to release inflammatory molecular messengers (called proinflammatory cytokines), while excessive amounts of saturated fat may also be linked to inflammation.

What foods prevent inflammation?
Similarly, foods that are commonly believed to be “anti-inflammatory” include vegetables (especially dark, leafy greens), fruits (especially berries), nuts, oily fish (salmon, mackerel, sardines), fiber-dense foods (whole grains, beans), olive oil, and green tea.

What about coffee?
Coffee might help prevent inflammation, although it appears to affect different people in different ways.

I feel like I’ve seen everywhere that turmeric is anti-inflammatory. How real is that? I hate turmeric.
Studies on the anti-inflammatory properties of turmeric (and the curcumin it contains) have been mixed; a large 2018 Canadian study (summarized in an accompanying editorial) found no anti-inflammatory benefit among postoperative patients taking turmeric.

Is anger inflammation?
Well, kind of. I included this as a joke at first, but mental stress — and specifically the stress hormone cortisol — is associated with higher levels of inflammation. Frequent bouts of anger (or long-lasting, low-simmering anger, or any feelings of stressful tension) could potentially contribute to chronic stress and, therefore, inflammation. A more likely culprit is long-lasting anxiety, although sometimes it can be hard to differentiate.

That is itself stressful and inflaming.
I know!

Can I step into a box that will quantify my exact levels of inflammation?
Not yet.

Just tell me if I’m inflamed.
We’re all probably a little inflamed.

What Is Inflammation, and Why Is Everyone Talking About It?