Whether it's the result of a sprained ankle, an allergic reaction to pollen, or an infected splinter, we all recognise the heat, swelling and discomfort that inflammation brings.
But while these complaints may seem relatively trivial, inflammation is far from being just skin deep. Increasingly, a low-level form of this reaction inside the body is recognised as being at the heart of most, if not all, common chronic diseases.
From diabetes to atherosclerosis, the eye condition age-related macular degeneration and even dementia, inflammation may be the silent killer that links them all.
Although clues about the importance of chronic inflammation have been there for a long time, it wasn't until 15 years ago that scientists really started taking it seriously.
'Even diseases which we have traditionally thought of as degenerative, such as dementia, are turning out to have a major inflammatory component,' says Professor Paul Morgan, an immunologist at Cardiff University.
The good news is that this could prompt a whole new approach to treating such illnesses using anti-inflammatory drugs. Better still, many of these drugs already exist; you probably even have some of them in your bathroom cabinet.
Under normal circumstances, inflammation is an extremely effective way of clearing up infection and promoting healing.
'Inflammation gets turned on by the immune system when trouble is spotted, whether it's due to infection or tissue damage,' says Graham Rook, emeritus professor of medical microbiology at University College London. 'It has three jobs to do: kill off the infection, clear up the mess, and help to repair the damage.'
The body brings about inflammation through the release of chemicals that summon immune cells to sites of trouble, and make the blood vessels leaky enough to enable these cells to infiltrate the damaged tissue. This is what causes the swelling and redness associated with inflammation. The immune cells then kill off the infection by releasing further chemicals, or gobbling up the invading virus or bacteria.
Generally speaking, inflammation is a good thing. It's likely that people who could mount a strong inflammatory response would have been at an evolutionary advantage, as they'd have been more likely to survive long enough to reproduce. The trouble only comes if the inflammation isn't switched off and becomes chronic and more widespread.
If inflammation does stay switched on, then the risk of 'friendly-fire' elsewhere in the body starts to outweigh the benefits.
Studies have suggested that this kind of chronic, low-grade inflammation - a kind of smouldering fire in our cells and tissues - is more common in rich Western populations than in more traditional societies.
With this kind of low-grade inflammation, you probably won't realise you have it, though doctors can measure inflammation by looking at levels of a substance called C-reactive protein (CRP) in the blood.
'If you take regular blood samples from people living in America or the UK, you find a lot of people who have no apparent infection but who have a fixed raised level of CRP for no apparent reason,' says Professor Rook.
That's a marked difference from, for example, indigenous populations living in the Ecuadorian Amazon, as a recent study in the American Journal of Human Biology suggested.
Regular blood samples from people in America or the UK would show many with no apparent infection but who have a raised level of CRP 'What you find there is that every now and then an individual will have enormously raised levels of CRP because they have an infection, but when it clears their levels of CRP will go down to zero,' says Professor Rook.
In other words, their off-switch really means off - whereas in Western populations, a pilot light is left constantly burning.
The cause of chronic inflammation is up for debate. Professor Rook suspects it's down to a change in our relationship with so-called 'old friends' - bacteria and parasites that we've lived with peacefully for much of human history.
Now that we're living cleaner lives, our immune systems are no longer receiving the same input they would have done during the first two to three years of life, and so are more likely to unleash inflammation at the slightest stimulus. It's a similar theory to the rise in allergies and auto-immune disease: the body overreacts to even minor threats. But there may be other explanations, too, such as rising levels of obesity.
Fat cells release some of the same inflammatory substances that are produced in response to infection and injury, and people with a higher body mass index have higher levels of inflammatory markers.
Then there's the fact we're all living longer lives, meaning there's more time for inflammation in response to everyday wear and tear to accumulate. 'Often it's very hard to pin down a single thing as the trigger for chronic inflammation,' says Professor Morgan. 'Probably, in most people, it is a combination of things that provides the initial trigger.'
Once established, though, that smouldering fire can have multiple effects. Take type 2 diabetes: for several decades, scientists have noticed higher levels of inflammation in patients with the condition.
It is now thought inflammatory chemicals released by fat cells (many people with type 2 are overweight) make tissues less sensitive to the effects of insulin, resulting in raised blood sugar levels, and these can promote yet more inflammation. Fat on your belly, and which can wrap around your organs - visceral fat - is thought to be the biggest culprit.
It's a similar story with age-related macular degeneration (AMD), a leading cause of blindness in older people which is caused by damage to the macula, the area of the eye responsible for central vision. Here, damage brought about by everyday exposure to stressors such as chemicals and bacteria triggers inflammation and tissue damage.
Many of the AMD drugs currently under development aim to reduce inflammation and stop the disease from progressing.
There's a growing consensus that inflammation elsewhere in the body can also affect the brain - possibly resulting in diseases, such as dementia, as well as depression and schizophrenia.
Even 100 years ago, doctors recognised that serious infections could trigger delirium - characterised by extreme confusion and hallucinations. Having a fever can also make people feel lethargic and depressed. For a long time, such observations were considered a mystery, because the brain was thought to be physically isolated from the immune system by the blood-brain barrier.
We now know this isn't strictly true. In fact, inflammatory chemicals can get into the brain and, once there, they activate resident immune cells called microglia, which produce more inflammatory substances as a result.
'That leads to increasing levels of toxic molecules within the brain, while levels of other chemicals, such as serotonin (important for regulating mood), decrease,' says Golam Khandaker, a psychiatrist at Cambridge University. 'This is very relevant for something like depression, where the problem is feeling low in mood and not being able to think straight.'
Here, too, anti-inflammatory drugs could help. For instance, a 2012 study found that a daily aspirin reduced the risk of depression by 40 per cent in elderly men with a history of the condition - although more research is needed.
What if you're healthy but are worried you might have undiagnosed inflammation that could be boosting your risk of future disease?
Popping anti-inflammatory drugs such as aspirin or ibuprofen as a long-term prophylactic isn't a great idea, because of possible side-effects such as stomach bleeds.
Dr Khandaker suggests looking at your diet. While a diet rich in sugar and the trans-fats found in some processed foods has been shown to boost inflammation, one rich in oily fish, fruit and vegetables has been shown to reduce it.
'We know that regular exercise and a healthy diet leads to a reduced risk of heart disease, depression, diabetes, you name it,' says Dr Khandaker.
'Recent work also shows exercise and a healthy diet lead to a reduction in inflammation in our bodies, so it's possible that this is how the mechanism works.'