What Causes Inflammation?


Inflammation is a complex biological response of our body to harmful stimuli and pathogens that consists of five cardinal signs, i.e., Redness (rubor), swelling (tumour), heat (calor), pain (dolor), and loss of function (function laesa). Inflammation is the body’s defense mechanism against harmful stimuli. It involves various cells of our immune system, including neutrophils, macrophages, monocytes, lymphocytes, and monocytes. It is considered as the response of our innate immunity. 

What are the Causes of Inflammation? 

There are various causes of inflammation that include physical, chemical, biological, and environmental causes. 

  • Physical causes include frostbite, trauma, blunt injury, burns, etc
  • Environmental causes include splinters, dirt, debris, ionizing radiation. 
  • Chemical causes include toxins, alcohol, toxic gases like carbon monoxide, etc
  • Biological causes include pathogens like bacteria, fungi, viruses, parasites, etc., stress, hypersensitivity reactions. 
  • Psychological causes include excitement. 

How do toxins cause inflammation?

Toxins like carbon monoxide, benzene, halocarbons, ketones, nitrosamines, etc., cause the production of reactive oxygen species in our body. These free radicals react with normal body tissues and destroy them, causing chronic inflammatory conditions. 

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How do certain foods cause inflammation?

Inflammation in response to certain foods is due to a hypersensitivity reaction. A person is sensitive to that food; consuming this food leads to an immune response called food allergy. Moreover:

  • Consuming food with high sucrose content causes inflammation by counteracting the anti-inflammatory effects of omega 3 fatty acids.
  • Artificial trans fats also increase the risk of inflammation and cardiovascular disorders. It occurs due to decreased HDL cholesterol and impaired functions of endothelial cells in vessels which leads to cardiovascular diseases. 
  • Vegetables and seed oils also promote inflammation because of their omega 6 fatty acid content.
  • Refined carbohydrates increase the risk of inflammation. It occurs because refined carbohydrates have no fibers. They increase glucose levels and promote inflammation.
  • Excessive alcohol intake causes inflammation, increases TAG levels, and leads to Fatty liver. 

What are the types of inflammation

There are two types of inflammation:

  • Acute inflammation
  • Chronic inflammation

What is acute inflammation?

Acute inflammation is a short-term process that is a response to tissue injury. It appears in minutes or hours after injury. It involves neutrophils and lymphocytes. 

Mechanism of acute inflammation:

It involves the following steps:

Recognition of microbes or foreign agents:

Cells have certain receptors called Toll-like receptors that recognize the foreign agents and microbes. Certain plasma proteins and cytosolic sensors of cell damage are also involved in recognition of microbes.

Vascular events:

When tissue injury occurs,  there is increased blood flow and increased vascular permeability. At first, there is transient vasoconstriction followed by vasodilation. Vasodilation causes increased vascular permeability; as a result, there is leakage of fluid out of vessels, which causes hemoconcentration that leads to slowing of blood flow. Slowing of blood flow causes arrangement of WBCS along vessel walls or Margination.  


The cells adhere to the endothelium, detach and adhere; this process is Rolling.

Permanent adhesion:

Cells attach to the endothelium permanently; it involves LFA, ECAM, PCAM.


The next step is the recruitment of leukocytes and neutrophils towards the inflammation site; it occurs by chemotaxis. In chemotaxis, certain chemicals attract neutrophils towards the site of inflammation. These include products of phagocytosis, chemokines, and components of complement like C5a. 


Once neutrophils reach the damaged area, they begin phagocytosis. At first, there is the formation of the phagosome. Later, the phagosome is destroyed by reactive oxygen species (ROS). 


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Outcomes of acute inflammation: 

  • Complete resolution
  • Fibrosis and scar formation
  • Chronic inflammation
  • Abscess formation

Mediators of acute inflammation:

  • For vasodilation: Histamine, Leukotrienes (LTC4, LTD4), Bradykinin, Prostaglandins (PGI2, PGE2, PGD2, PGF2) Complement (C3a, C5a), 
  • For chemotaxis: Interleukins (IL-8), PAF, Complement (C5a), Histamine 
  • For phagocytosis: C3b
  • Fever:
  • Interleukins (IL-1, IL-6), TNF-α, 
  • Pain:
  • Prostaglandins (PGE2), Bradykinin, Histamine

Chronic inflammation:

Chronic inflammation is a long-term response to tissue damage or inflammatory stimuli. It is characterized by macrophages and lymphocytes.  It occurs when: 

  • The agents causing inflammation like mycobacterium tuberculosis, bacteria, fungi, viruses, etc., are not removed from the body. The inflammation, as well as the attempts of tissue repair, coexist. 
  • Acute inflammation leads to chronic inflammation when the damaging stimulus is not removed.
  • Autoimmune disorders like rheumatoid arthritis in which body tissues are recognized as foreign agents and immune responses are produced. 
  • Oxidative stress and mitochondrial dysfunction
  • Continuous exposure to low levels of chemical irritants or toxins

Mechanism of chronic inflammation: 

Progression of acute inflammation to chronic inflammation results in the production of macrophages and lymphocytes. They are activated by chemokines and cytokines, and they also release cytokines and other mediators of inflammation. Phagocytosis occurs as a result, by macrophages.

Role of macrophages: 

Macrophages are recognized as the central player of inflammation. They are derived from monocytes in the circulating blood.  Activation of macrophages causes an increase in protein synthesis, size, and phagocytic activity of lysosomes. They also produce certain mediators of inflammation like interferon-alpha and -beta, interleukin-1, -6 and -8, TNF-alpha, etc.  M1 macrophages are involved in all this and caus phagocytosis.

M2 macrophages produce interleukin 10. They cause remodeling, angiogenesis, scavenging and are also involved in the repair process.

Diseases involving chronic inflammation: 

Mediators of chronic inflammation:

Mediators of chronic inflammation are leukotrienes, prostaglandins, kinins,  interleukin, and platelet-activating factors.

Patterns of inflammation:

There are the following patterns of inflammation:

  • Serous inflammation that involves watery, protein neutrophils rich effusion. For example, in blisters. 
  • Fibrinous inflammation in which a large amount of fibrin deposition occurs. 
  • Abscess formation in which localized collection of fluid occurs inside the tissue. 
  • Suppurative inflammation in which suppuration occurs in deeper body tissues. 
  • Ulceration in which mucosa of mouth, stomach, or endothelium is digested and shed off.

Granulomatous inflammation: 

In granulomatous inflammation,  there is a  collection of macrophages, giant cells, and epitheloid cells. There is the formation of granulomas that are the accumulation of macrophages surrounded by epithelial cells. 

Diseases involving granulomatous inflammation include:

  • Tuberculosis
  • Crohn’s disease
  • Berylliosis
  • Cat scratch disease
  • Syphilis
  • Leprosy
  • Histoplasmosis
  • Schistosomiasis 
  • Rheumatic fever
  • Sarcoidosis 

Getting Started

Inflammation is a complex biological response as well as an indicator of cell damage. There are two types of inflammation, acute and chronic. Acute inflammation involves redness, heat,  pain, swelling, and loss of function. Chronic inflammation involves persistent infection or autoimmune disorders. Neutrophils are involved in acute inflammation, while macrophages are involved in chronic inflammation. Chronic inflammation indicates the presence of various diseases. 

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