This might be the most important thing to know about inflammation: When it does what it's supposed to do, it's a good thing. The Walter & Eliza Hall Institute for Medical Research explains that inflammation helps out the body in many ways, including "increasing blood flow and movement of immune cells into the inflamed tissue; stimulating immune cells, such as triggering macrophages to be more likely to engulf nearby substances; [and] stimulating production of new immune cells". Vaccines, they note, usually trigger inflammation that helps the immune system remember threats and how to fight them in the future.

High levels of inflammation, specifically in the brain, have been shown to be tied to depression, though it's not clear whether it's cause or effect — whether people who have depression have higher inflammation in their bodies because of their mental health, or if inflammation causes neurological symptoms that influence depression.

Research from Cambridge in 2019 found that people with depression tend to have higher than normal rates of heart disease because of the presence of inflammation, often related to stress. If you're stressed and depressed, your higher inflammation levels leave you more vulnerable to heart conditions.

Chronic inflammation is a condition where inflammation levels are persistently high, despite there being nothing for the immune system to "fight off." It's the mechanism behind long-term illnesses like rheumatoid arthritis, and research has also linked it to increased risk of Alzheimer's disease.

Obstructive sleep apnea, a condition where you stop breathing in the night because your airways close, has been shown to cause inflammation levels to rise. Mysteriously, men are far more likely than women to have obstructive sleep apnea.

Polycystic ovary syndrome, where ovaries are prone to developing cysts, has also been tied to low-grade chronic inflammation levels in the body.

The Harvard Medical School notes that "experimental studies" have shown that foods including tomatoes and green leafy veg fight inflammation, while white bread, processed meat and sugary drinks can increase it. Too much alcohol can also increase inflammation levels.

To lower your inflammation levels, it's a good idea to eat foods like oily fish; studies have shown that omega-3 fatty acids are good for lowering inflammation levels.

Dark chocolate may actually have anti-inflammatory properties, because it's got anti-oxidants and not too much sugar.

If you're seriously stressed, you're more likely to be ill — and one of the ways in which this happens, according to science from 2012, is that stress triggers inflammatory responses that then make the body less likely to fight off illnesses.

If you have a sleep disorder like insomnia, according to a study in 2018, inflammation may be the cause, as it can disrupt the body's internal circadian rhythms, making sleep less restful, more irregular or more fragmented.

This relationship goes both ways; sleeping poorly can set off inflammation in the body, according to a study published in 2016.

The existence of chronic inflammation, explained the Johns Hopkins Health Review in 2016, is cyclical. "Researchers have an idea that inflammation exists as part of a self-reinforcing loop system. If they could figure out how to interrupt or reverse one stage in that loop, then they might be able to develop drugs to stop it. But how do you tone down the immune response enough to control the inflammation but not so much that a body can’t fight disease?" There's no clear answer yet.

Inflammation is actually a response to food in general. A study in 2017 found that our inflammation markers increase after every meal, before quickly dropping back to normal again as the body identifies and digests what's been eaten.

The National Cancer Institute explains that chronic inflammation can cause cancer because of its long-term damage to DNA, which causes problems in the replication of cells that can lead to cancers.

Just because it's not a cigarette doesn't mean it isn't dangerous; a study in 2018 found that, like smoking, e-smoking causes spikes in inflammation levels in the body when used.

Children who are breast fed are known to have a lot of boosts, but a study published in 2015 showed that that might have to do with anti-inflammatory substances in breast milk.

Even though the muscle strain you want from exercise induces a short amount of inflammation (see #1), research in 2017 found that a single 20-minute session of moderate exercise can trigger an anti-inflammatory response in the body.

When it comes to severe, long-term inflammation, there's lots of work being done to figure it out. One 2018 study revealed an "electrical switch" that might turn chronic inflammation off, while another study the same year discovered a "molecular lock" that could yield treatments for inflammatory bowel disease.

The most common way to test inflammation levels in the body is a C-reactive protein blood test; C-reactive proteins rise in response to inflammation, so high levels of them tend to indicate inflammatory responses. However, one day tests might be more complex and refined; researchers in 2019 revealed they were developing a tool to test the effects of anti-inflammatory drugs, which one day might be used to probe exactly how inflammation affects very small areas of the body.

Inflammation isn't the end of the world, but at persistent chronic levels it can be linked to illnesses and conditions that can make your life more difficult. If you're worried, talk to your doctor about testing your inflammation levels and ways to reduce it.