What Is Inflammation? What Causes Inflammation?

Inflammation is the body's attempt at self-protection; the aim being to remove harmful stimuli, including damaged cells, irritants, or pathogens - and begin the healing process.

When something harmful or irritating affects a part of our body, there is a biological response to try to remove it, the signs and symptoms of inflammation, specifically acute inflammation, show that the body is trying to heal itself. Inflammation does not mean infection, even when an infection causes inflammation. Infection is caused by a bacterium, virus or fungus, while inflammation is the body's response to it.

The word inflammation comes from the Latin "inflammo", meaning "I set alight, I ignite".

Inflammation is part of the body's immune response. Initially, it is beneficial when, for example, your knee sustains a blow and tissues need care and protection. However, sometimes inflammation can cause further inflammation; it can become self-perpetuating. More inflammation is created in response to the existing inflammation.

According to Medilexicon's medical dictionaryInflammation is:

"A fundamental pathologic process consisting of a dynamic complex of histologically apparent cytologic changes, cellular infiltration, and mediator release that occurs in the affected blood vessels and adjacent tissues in response to an injury or abnormal stimulation caused by a physical, chemical, or biologic agent, including the local reactions and resulting morphologic changes; the destruction or removal of the injurious material; and the responses that lead to repair and healing.

The so-called cardinal signs of inflammation are rubor, redness; calor, heat (or warmth); tumor, swelling; and dolor, pain; a fifth sign, functio laesa, inhibited or lost function, is sometimes added. All these signs may be observed in certain instances, but none is necessarily always present."

Plaque in coronary artery disease linked to inflammation - scientists from Stanford University, California, linked 25 new genetic regions to coronary artery disease. They found that people with coronary artery disease, the leading cause of death globally, are most likely predisposed to the disease because they have gene variants linked to inflammation.

Inflammation helps wounds heal

Wrist inflammation

Our immediate reaction to a swelling is to try to bring it down. Bearing in mind that inflammation is an essential part of the body's attempt to heal itself, patients and doctors need to be sure that the treatments to reduce swelling are absolutely necessary and to not undermine or slow down the healing process.

The first stage of inflammation is often called irritation, which then becomes inflammation - the immediate healing process. Inflammation is followed by suppuration (discharging of pus). Then there is the granulation stage, the formation in wounds of tiny, rounded masses of tissue during healing. Inflammation is part of a complex biological response to harmful stimuli. Without inflammation, infections and wounds would never heal.

Neuroscientists at the Lerner Research Institute at the Cleveland Clinic in Ohio found thatinflammation actually helps to heal damaged muscle tissue. Their findings clash with how sportspeople with inflammation are treated - health professionals always try to control the inflammation to encourage healing. The researchers say their findings may lead to new therapies for acute muscle injuries caused by freeze damage, medications, chemicals and trauma.

Lan Zhou, M.D., Ph.D., said that patients should be very closely monitored when therapies to combat inflammation are used to make sure that the benefits of inflammation are not completely eliminated.

Inflammation is part of our innate immunity

Our innate immunity is what is naturally present in our bodies when we are born, and not theadaptive immunity we get after an infection or vaccination. Innate immunity is generally non-specific, while adaptive immunity is specific to one pathogen:

Whooping cough vaccine - example of immunity being specific to one pathogen

      After being vaccinated for whooping cough (pertussis), we develop immunity to

Bordetella pertussis


Bordetella parapertussis

    , types of bacteria that cause pertussis. This is an example of adaptive immunity - the immunity was not there before receiving the vaccine.

Inflammation is seen as a mechanism of innate immunity.

What is the difference between chronic inflammation and acute inflammation?

Acute inflammation - starts rapidly (rapid onset) and quickly becomes severe. Signs and symptoms are only present for a few days, but in some cases may persist for a few weeks.

Examples of diseases, conditions, and situations which can result in acute inflammation include: acute bronchitis, infected ingrown toenailsore throat from a cold or flu, a scratch/cut on the skin, exercise (especially intense training), acute appendicitis, acute dermatitis, acute tonsillitis, acute infective meningitis, acute sinusitis, or a blow.

Chronic inflammation - this means long-term inflammation, which can last for several months and even years. It can result from:

  • Failure to eliminate whatever was causing an acute inflammation
  • An autoimmune response to a self antigen - the immune system attacks healthy tissue, mistaking it (them) for harmful pathogens.
  • A chronic irritant of low intensity that persists

Examples of diseases and conditions with chronic inflammation include: asthma, chronic peptic ulcertuberculosisrheumatoid arthritis, chronic periodontitis, ulcerative colitis and Crohn's disease, chronic sinusitis, and chronic active hepatitis (there are many more).

Our infections, wounds and any damage to tissue would never health without inflammation - tissue would become more and more damaged and the body, or any organism, would eventually perish.

However, chronic inflammation can eventually cause several diseases and conditions, including some cancers, rheumatoid arthritis, atherosclerosis, periodontitis, and hay fever. Inflammation needs to be well regulated.

What happens during acute inflammation?

Within a few seconds or minutes after tissue is injured, acute inflammation starts to occur. The damage may be a physical one, or might be caused by an immune response.

Three main processes occur before and during acute inflammation:

    • Arterioles, small branches of arteries that lead to capillaries that supply blood to the damaged region dilate, resulting in increased blood flow


    • The capillaries become more permeable, so fluid and blood proteins can move into interstitial spaces (spaces between tissues).


  • Neutrophils, and possibly some macrophages migrate out of the capillaries and venules (small veins that go from a capillary to a vein) and move into interstitial spaces. A neutrophil is a type of granulocyte (white blood cell), it is filled with tiny sacs which contain enzymes that digest microorganisms. Macrophages are also a type of white blood cells that ingests foreign material.

    Klaus Ley, M.D., a scientist at the La Jolla Institute for Allergy & Immunology, reported in a study published in Nature that neutrophils are the human body's first line of defense; they are the main cells that protect us from bacterial infections. Their protective function is a positive one, however, they also have inflammatory properties that may eventually lead toheart disease and several autoimmune diseases, such as lupus. Effectively manipulating neutrophils is vital in disrupting inflammatory diseases.

When our skin is scratched (and the skin is not broken), one may see a pale red line. Soon the area around that scratch goes red, this is because the arterioles have dilated and the capillaries have filled up with blood and become more permeable, allowing fluid and blood proteins to move into the space between tissues.

Edema - the area then swells as further fluid builds up in the interstitial spaces.

The five cardinal signs of acute inflammation - "PRISH"

An ingrown toenail
An ingrown toenail with the five PRISH signs; pain, redness, immobility, swelling and heat
  • Pain - the inflamed area is likely to be painful, especially when touched. Chemicals that stimulate nerve endings are released, making the area much more sensitive.
  • Redness - this is because the capillaries are filled up with more blood than usual
  • Immobility - there may be some loss of function
  • Swelling - caused by an accumulation of fluid
  • Heat - as with the reason for the redness, more blood in the affected area makes it feel hot to the touch

The five classical signs of inflammation

Although Latin terms are still used widely in Western medicine, local language terms, such as English, are taking over. PRISH is a more modern acronym which refers to the signs of inflammation. The traditional Latin based terms have been around for two thousand years:

  • Dolor - Latin term for "pain"
  • Calor - Latin term for "heat"
  • Rubor - which in Latin means "redness"
  • Tumor - a Latin term for "swelling"
  • Functio laesa - which in Latin means "injured function", which can also mean loss of function

Dolor, Calor, Rubor, and Tumor were first described and documented by Aulus Cornelius Celsus (ca 25 BC-ca 50), a Roman encyclopaedist. Celcius is famous for creating De Medicina, which is thought to be the only surviving section of a vast encyclopedia. De Medicina was the main source of medical reference in the Roman world for pharmacy, surgery, diet and some other medical fields.

Functio laesa - it is not clear who first described and documented the fifth sign. The majority of attributions have gone to Thomas Sydenham (1624-1689) an English physician and Rudolph Carl Virchow (1821-1902), a German doctor, biologist, politician and pathologist. Virchow is seen as one of the founders of social medicine.

These five acute inflammation signs are only relevant when the affected area is on or very close to the skin. When inflammation occurs deep inside the body, such as an internal organ, only some of the signs may be detectable. Some internal organs may not have sensory nerve endings nearby, so there is be no pain, as is the case with some types of pneumonia (acute inflammation of the lung). If the inflammation from pneumonia pushes against the parietal pleura (inner lining of the surface of the chest wall), then there is pain.

Acute and chronic inflammation compared

The lists below show the difference between chronic and acute inflammation regarding the causative agents, which major cells are involved, features regarding onset, duration, and outcomes:

Acute Inflammation

  • Causative agents - harmful bacteria or injury to tissue
  • Major cells involved - mainly neutrophils, basophils (in the inflammatory response), and eosinophils (response to parasites and worms), and mononuclear cells (macrophages, monocytes)
  • Primary mediators - eicosanoids, vasoactive amines
  • Onset (when does the inflammation start) - straight away
  • Duration - short-lived, only a few days
  • Outcomes - the inflammation either gets better (resolution), develops into an abscess, or becomes a chronic inflammation

Chronic inflammation

  • Causative agent - non-degradable pathogens that cause persistent inflammation, infection with some types of viruses, persistent foreign bodies, overactive immune system reactions
  • Major cells involved - Macrophages, lymphocytes, plasma cells (these three are mononuclear cells), and fibroblasts
  • Primary mediators - reactive oxygen species, hydrolytic enzymes, IFN-γ and other cytokines, growth factors
  • Duration - from several months to years
  • Outcomes - the destruction of tissue, thickening and scarring of connective tissue (fibrosis), death of cells or tissues (necrosis)

Sleep quality and duration impacts on inflammation risk

Scientists at Emory University School of Medicine in Atlanta, Georgia, found in a study thatsleep deprivation or poor sleep quality raise inflammation, which in turn increase the risk of developing heart disease and stroke.

The team gathered data on 525 middle-aged volunteers who had completed the Pittsburgh Sleep Quality Index (PSQI) questionnaire, which asked detailed questions about sleep quality and duration.

They tested the participants' levels of various inflammatory markers, and then tried to see whether they could link them to quality and duration of sleep. The authors concluded:

"The researchers concluded that: "Poor sleep quality, and short sleep durations are associated with higher levels of inflammation."

Why does inflammation cause pain?

What is pain? When people have inflammation it often hurts, they feel pain, stiffness, discomfort, distress and perhaps agony, depending on the severity of it. Pain can be constant and steady, in which case it is often referred to as an ache. Pain can be of a throbbing type, a pulsating pain, or it can be a stabbing or pinching pain.

Pain is a very individual experience and the only person who can describe it properly is the one who is feeling it.

Pain can be acute or chronic. It can also be:

    • Nociceptive pain - specific receptors are stimulated for us to feel this type of pain. These receptors sense changes in temperature, vibration, stretch, and chemicals which damaged cells release. "Nociceptive" means causing or reacting to pain - the cause of the pain comes from outside the nervous system, and the nervous system reacts to it. "Non-nociceptive" means the pain comes from within the nervous system itself.


    • Somatic pain - this is a kind of nociceptive pain. The sensation is felt in muscles, joints, bones, ligaments, and on the skin. Musculo-skeletal pain is somatic pain. Pain receptors are sentive to stretch in the muscles, vibration, temperature, as well as inflammation. When there is a lack of oxygen there may be painful ischemic muscle cramps.

      Somatic pain tends to be sharp and localized - touching or moving the affected area will result in more severe main.


    • Visceral pain - this is a kind of nociceptive pain. Pain is sensed deep down in the body, in the internal organs and main body cavities, such as the heart, lungs, bowels, spleen, liver, kidneys, bladder, uterus, and ovaries. The nociceptors (pain receptors) sense oxygen starvation (ischemia), stretch, and inflammation. It is harder to localize visceral pain than somatic pain. The pain is usually described as a deep ache. Cramping and colicky sensations are examples of visceral pain.

Inflammation primarily causes pain because the swelling pushes against the sensitive nerve endings, which send pain signals to the brain. Nerve endings send pain signals to the brain all day long; however, it learns to ignore most of them, unless pressure against the nerve endings increases.

Other biochemical processes also occur during inflammation which affect how nerves behave, and cause pain.

Inflammation risk much greater if you are obese

Diagram of painful joints in obese male
example of common painful joints in an overweight male

Fat men have more inflammatory markers(white blood cells) than men of the same age who are not obese or overweight. Raised white blood cell levels are markers which are linked to a higher risk of developing various illnesses, including coronary heart disease.

In a recent study, a team from Pennington Biomedical Research Center in Baton Rouge, Louisiana, focused on specific types of white blood cells; neutrophils, lymphocytes, monocytes, basophils, and eosinophils.

They measured resting levels of the white blood cells in the adult males, as well as their levels of fitness and BMIs (body mass indexes), and adjusted the results for age.

They found that:

  • Unfit men had higher white blood cell levels that fit men
  • Men with higher BMIs had raised levels of white blood cells
  • The combination of fitness levels and body weights impacted considerably on levels of white blood cells, and ultimately inflammation

Although scientists know that inflammation plays a key role in heart disease and several other illnesses, what drives inflammation in the first place is still a mystery.

Inflammation drops when women lose weight - scientists at the Fred Hutchinson Cancer Research Center in Seattle, Washington found that postmenopausal overweight or obese women who lost 5% or more of their body weight had measurable falls in levels of inflammation markers. Team leader, Anne McTiernan, M.D., Ph.D., said "Both obesity and inflammation have been shown to be related to several types of cancer, and this study shows that if you reduce weight, you can reduce inflammation as well."

Autoimmune disorders and inflammation

An autoimmune disease, also known as autoimmune disorder, is one where the body initiates an immune response to healthy tissues, mistaking them for harmful pathogens or irritants. The immune response triggers an inflammatory response too.

There are literally hundreds of autoimmune diseases, and nearly all of them have inflammation as one of the signs, examples include:

    • Rheumatoid arthritis - there is inflammation in the joins, tissues surrounding the joints, and sometimes some other organs in the body


    • Ankylosing Spondylitis - there is inflammation of the vertebrae, muscles, ligaments, and also the sacroiliac joints (where the spine and hips meet)


    • Celiac Disease - there is inflammation and destruction of the inner lining of the small intestine.


    • Crohn's Disease - the gastrointestinal tract becomes inflamed. Inflammation is most common in the ileum (small intestine), but may occur anywhere in the GI tract, from the mouth to the anus.


    • Fibromyalgia - often a set of symptoms related to another autoimmune disorder, such as lupus or rheumatoid arthritis. There is pain in various parts of the body. Location and even the existence of inflammation is unclear.


    • Graves' Disease - one of the signs is goiter; when the thyroid gland is inflamed.Exophthalmos, inflammation of the muscles behind the eyes. Grave's dermopathy, inflammation of the skin, usually the shins and the top of feet (uncommon)


    • Idiopathic Pulmonary Fibrosis - the role of inflammation is unclear. Experts used to think that the disease was mainly caused by inflammation within the alveoli (tiny sacs within the lungs). However, treatments to reduce inflammation are often disappointing. Therefore, although there is inflammation, its impact on the disease is a bit of a mystery.


    • Lupus - there can be inflammation in the joints, lungs, heart, kidney and skin.


    • Psoriasis - there is inflammation of the skin. In some cases, as in psoriatic arthritis, the joints and tissue surrounding the joints may also become inflamed.


    • Type 1 Diabetes - inflammation in various parts of the body are likely if the diabetes is not well controlled.


    • Addison's disease - inflammation of the adrenal glands. The stress to the body caused by this disease can also lead to inflammation elsewhere.


    • Vaslculitis - refers to a group of disorders in which inflammation eventually destroys blood vessels, both arteries and veins.


    • Transplant rejection - there is already substantial inflammation caused by the transplant operation. If the organ recipient's immune system rejects the new organ, there is typically inflammation in and around the donated organ.


    • Various allergies - all allergies have inflammation. Asthma has inflammation of the airways, in hay fever the nose, ear and throat mucous membranes become inflamed, people who are allergic to bee stings may have serious life-threatening inflammation which affects the whole body (anaphylaxis).


  • Vitamin A deficiency - inflammatory responses are much more likely if the person is deficient in vitamin A.

The disorders mentioned above are just a tiny example of the hundreds of autoimmune disorders which have inflammation as one of their signs.

What are the possible treatments for inflammation

As mentioned earlier in this article, patients (and many health care professionals) must remember that inflammation is part of the healing process. Sometimes reducing inflammation is necessary, but not always.

Anti-inflammatory medications

Ibuprofen is commonly used to alleviate pain

NSAIDs (non-steroidal anti-inflammatory drugs) are taken to alleviate pain caused by inflammation. They counteract the COX (cyclooxygenase) enzyme, which synthesizes prostaglandins which create inflammation. If prostaglandin synthesis can be blocked, pain is either eliminated or reduced.

Examples of NSAIDs include naproxen, ibuprofen and aspirin.

People should not use NSAIDs long-term without being under the supervision of a doctor, because there is a risk of stomach ulcers, and even severe and life-threatening hemorrhage. NSAIDs may also worsen asthma symptoms and cause kidney damage. NSAID medications, with the exception of aspirin, can also increase the risk of stroke and myocardial infarction (heart attack).

Acetaminophen (paracetamol, Tylenol) can reduce pain associated with inflammatory conditions, but have no anti-inflammatory effects. They may be ideal for those wishing to treat just the pain, while allowing the inflammation to run its course.

Corticosteroids - these are a class of steroid hormones naturally produced in the cortex (outer portion) of the adrenal gland. They are synthesized in laboratories and added to medications.

Corticosteroids, such as cortisol are anti-inflammatory; they prevent phospholipid release, which undermines eosinophil action and a number of other mechanisms involved in inflammation.

There are two sets of corticosteroids:

    • Glucocorticoids, which are produced as a reaction to stress, and are also involved in metabolizing fats, proteins and carbohydrates. Synthetic glucocorticoids are prescribed for inflammation of the joints (arthritis), temporal arteritis dermatitis, inflammatory bowel disease, systemic lupus, hepatitis, asthma, allergic reactions, and sarcoidosis. Creams and ointments (topical formulations) may be prescribed for inflammation of the skin, eyes, lungs, bowels and nose.


    • Mineralocorticoids, which regulate our salt and water balance. Medications with mineral corticoids are used for the treatment of cerebral salt wasting, and to replace missing aldosterone (a hormone) for patients with adrenal insufficiency.

Corticosteroid side effects are more likely if taken in oral form, compared to inhalers or injections. The higher the dosage and/or the longer they are taken for, the greater the risk of side effects. Side effect severity is also linked to dosage and duration of treatment. Patients taking oral corticosteroids for over three months have a considerably greater chance of experiencing undesirable side effects. Inhaled medications, such as those to treat asthma over the long-term raise the risk of developing oral thrush - rinsing the mouth out with water after each application can help prevent oral thrush. Gucocorticoids can also induce Cushing's syndrome, while mineralocorticoids can cause high blood pressure (hypertension), low blood potassium levels (hypokalemia), high blood-sodium levels (hypernatremia), connective tissue weakness and metabolic alkalosis.

ImSAIDs (Immune Selective Anti-Inflammatory Derivatives)

ImSAIDs are a class of peptides being developed by IMULAN BioTherapeutics, LLC. Scientists found that they have anti-inflammatory properties. They alter the activation and migration of immune cells involved in amplifying the inflammatory response. This is a new category of anti-inflammatory medication which has nothing to do with steroids or non-steroidal anti-inflammatories. ImSAIDs have shown promise as potential veterinary drugs for controlling and reducing inflammation. Experts believe that they might eventually be suitable for human use.

Some herbs have anti-inflammatory properties

  • Harpagophytum procumbens - also known as devil's clawwood spider or grapple plant comes from South Africa and is related to sesame plants. European colonists brought devil's claw back home to treat arthritis, fever and pain. According to the British Herbal Pharmacopoeia, Devil's Claw has diuretic, sedative and analgesic properties.


  • Hyssop Hyssopus - from the plant family Lamiaceae, is added to eau de Cologne and Chartreuse (liqueur drink). It is also used to color some spirits. Hyssop is mixed with other herbs, such as liqourice for the treatment of some lung conditions, including inflammation. Beware of the essential oils of hyssop, as they can lead to life-threatening convulsions in laboratory animals.


  • Ginger, also known as ginger root, is the mass of roots (rhizome) of the Zingiber officinaleplant. It is used as a medicine or a spice. Jamaican ginger was the traditional medical form of this root, and has been used as a carminative (to treat gas or wind) and a stimulant. It has been used for hundreds of years to treat dyspepsiaconstipationcolic, other gastrointestinal problems, as well as rheumatoid arthritis pain.

    Researchers from Michigan Medical School reported that ginger supplements were found to reduce the markers of colon inflammation. Chronic colon inflammation is associated with a higher risk of developing colon cancer. They added that ginger supplements may help prevent colon cancer.


  • Turmeric (Curcuma longa) - also a plant of the ginger family. Current research is looking into the possible beneficial effects of turmeric in treating arthritis, Alzheimer's disease, and some other inflammatory conditions. Curcumin, a substance found in turmeric, is under investigation for the treatment of several illnesses and disorders, including inflammation.


  • Cannabis - contains a cannabinnoid called cannabichromene, which has been shown to have anti-inflammatory properties.

    Other treatments for inflammation

    Applying ice - do not place the ice in direct contact with skin, wrap it in a cloth or a purpose-made ice bag. Applying ice has been shown to reduce inflammation. Athletes commonly use ice treatment for managing pain and inflammation. Inflammation can go down more rapidly if you rest, apply ice, compression, and elevate the affected area (have your ankle raised if the swelling is there, for example).

    Fish oil (Omega-3) - scientists form Ohio State University Center for Clinical and Translational Science reported on a study in the journal Brain, Behavior and Immunity that the daily consumption of fish oil, omega-3 reduced both inflammation and anxiety in a group of young healthy people.

    Green tea - researchers from the Laura W. Bush Institute for Women's Health at the Texas Tech University Health Sciences Center found that regular green tea drinking enhances bone health and reduces inflammation in postmenopausal women. They added that Tai-Chi appears to have the same beneficial effect.

    Tart cherries - sports scientists found that tart cherries have powerful anti-inflammatory properties which may help millions of Americans who suffer from joint pain and arthritis. The team, from Oregon Health & Science University even went as far as saying that "(tart cherries) have the highest anti-inflammatory content of any food". They believe that tart cherries could help patients with osteoarthritis manage their pain effectively. Twenty females aged from 40 to 70 years drank tart cherry juice twice a day for three weeks; they all suffered from inflammatory osteoarthritis. At the end of the three weeks there were significant falls in levels of key inflammation markers.

    Written by Christian Nordqvist

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