Inflammation | Definition, Symptoms, Treatment, & Facts

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class="md-content"> <div class="md-article-container template-desktop infinite-pagination"> <div class="infinite-scroll-container article last"> <article class="article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content md-expanded" data-topic-id="287677"> <div class="grid gx-0"> <div class="col-auto"> <div class="topic-left-rail md-article-drawer position-relative d-flex border-right-sm border-left-sm open"> <div class="drawer d-flex flex-column open"> <div class="left-rail-section-content"> <div class="topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center"> <div class="tlr-title px-20 py-15 text-left"> <em class="material-icons text-gray-400 d-lg-none" data-icon="toc"></em> <a class="font-serif font-weight-bold text-black link-blue" href="https://www.britannica.com/science/inflammation">inflammation</a> </div> <button aria-label="Close" class="js-sections-close-button btn-link btn-sm btn d-lg-none position-absolute top-0 p-10 right-0" > <em class="material-icons font-26" data-icon="close"></em> </button> </div> <div class="section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 clear-catfish-ad"> <div class="toc mb-20"> <div class="font-serif font-14 font-weight-bold mx-15 mb-15 mt-20"> Table of Contents </div> <ul class="list-unstyled my-0" data-level="h1"><li data-target="#ref1"><div class="pl-25"><a class="link-gray-900 w-100" href="/science/inflammation">Introduction & Top Questions</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref214900"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/inflammation#ref214900">Causes</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref214901"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/inflammation#ref214901">Signs</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref214902"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/inflammation#ref214902">The acute inflammatory response</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref214903"><a class="w-100 link-gray-900" href="/science/inflammation#ref214903">Vascular changes</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref214904"><a class="w-100 link-gray-900" href="/science/inflammation/Cellular-changes">Cellular changes</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref214905"><a class="w-100 link-gray-900" href="/science/inflammation/Cellular-changes#ref214905">Chemical mediators of inflammation</a></li></ul></div></li><li data-target="#ref214906"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/inflammation/Cellular-changes#ref214906">Events following acute inflammation</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref214907"><a class="w-100 link-gray-900" href="/science/inflammation/Healing-and-repair">Healing and repair</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref214908"><a class="w-100 link-gray-900" href="/science/inflammation/Healing-and-repair#ref214908">Suppuration</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref214909"><a class="w-100 link-gray-900" href="/science/inflammation/Chronic-inflammation">Chronic inflammation</a></li></ul></div></li></ul> <a class="toc-extra-link link-gray-900" href="https://www.britannica.com/science/inflammation/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/inflammation">Related Topics</a> </div> <div class="tlr-media-slider pb-10 mb-30"> <a class="section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10" href="https://www.britannica.com/science/inflammation/images-videos">Images & Videos</a> <div class="slider js-slider position-relative d-inline-flex align-items-center mw-100 "> <div class="slider-container js-slider-container overflow-hidden d-flex overflow-hidden text-nowrap ml-15"> <a href="https://cdn.britannica.com/03/20903-004-379E4AF3/Pathways-complement-activation-function-proteins-cells-pathogens.jpg" data-href="/media/1/287677/17664" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" 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Some complement components also promote inflammation by stimulating cells to release histamine and by attracting phagocytic cells to the site of infection.</span></span> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"> <span class="link-blue">(more)</span> </button> </span> </div> </figcaption> </figure> </div><div class="topic-header"> <div class="d-flex align-items-top justify-content-between"> <div class="d-flex flex-column"> <div> <div> <h1>inflammation</h1></div> </div> <div class="topic-identifier font-16 font-md-20">pathology</div> </div> </div> <div class="d-none d-sm-flex flex-row"> <div class="mr-10 mb-15"> <button class="ai-ask-button btn border-2 btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400"> Ask the Chatbot a Question </button> </div> <div class="d-none d-sm-block md-topic-tools qa-action-buttons mb-15" data-topic-id="287677"> <button class="js-tooltip btn btn-sm btn-outline-blue border pr-10 border-2" > <em class="material-icons md-icon ml-n10 my-n5 mr-5" data-icon="more_vert"></em> More Actions </button> <div class="md-more-popover popover popover-sm p-0 font-14 z-1"> <div> <button class="js-print-modal-button js-modal gtm-topic-tool btn btn-sm btn-link gtm-topic-tool font-weight-bold btn-link" data-modal="[data-topic-id=287677] .md-print-modal" > <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="print"></em> Print </button> <div class="md-print-modal size-lg d-none"> <div class="md-modal-body"> <div class="h2 font-serif d-flex align-items-center pb-15 border-bottom"> <em class="material-icons text-blue mr-10">print</em> Print </div> <div class="mt-20 mb-10"> Please select which sections you would like to print: </div> <form action="/print/article/287677" method="post" target="_blank" rel="noopener"> <div class="print-box-items"> <ul class="list-unstyled"> <li><label><input class="mr-10" type="checkbox" name="sequence[]" value="0">Table Of Contents</label></li> </ul> </div> <input type="submit" class="btn btn-blue md-disabled" value="Print" /> </form> </div> </div> </div> <div> <button class="js-modal qa-cite-modal-button btn btn-sm btn-link gtm-topic-tool font-weight-bold btn-link" data-modal="[data-topic-id=287677] .md-cite-modal"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="verified"></em> Cite </button> <div class="md-cite-modal size-lg d-none"> <div class="md-modal-body"> <div class="h2 font-serif d-flex align-items-center pb-15 border-bottom mb-15"> <em class="material-icons text-blue mr-10">verified</em>Cite </div> <div class="font-serif"> While every effort has been made to follow citation style rules, there may be some discrepancies. 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The inflammatory response is a defense mechanism that evolved in higher organisms to protect them from infection and <a href=\"https:\/\/www.britannica.com\/science\/wound\">injury<\/a>. Its purpose is to localize and eliminate the injurious agent and to remove damaged tissue components so that the body can begin to heal. The response consists of changes in blood flow, an increase in permeability of blood vessels, and the migration of fluid, proteins, and white blood cells (<a href=\"https:\/\/www.britannica.com\/science\/white-blood-cell\">leukocytes<\/a>) from the circulation to the site of tissue damage. An inflammatory response that lasts only a few days is called acute inflammation, while a response of longer duration is referred to as chronic inflammation. " } } , { "@type" : "Question", "name" : "<div>What are the signs of inflammation? <\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "The four cardinal signs of inflammation are redness (Latin <em>rubor<\/em>), heat (<em>calor<\/em>), swelling (<em>tumor<\/em>), and pain (<em>dolor<\/em>)." } } , { "@type" : "Question", "name" : "<div>Is inflammation good or bad? <\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "Inflammation serves as a defense mechanism against infection and injury, and localizing and eliminating injurious factors and removing damaged <a href=\"https:\/\/www.britannica.com\/science\/tissue\">tissue<\/a> components allows the healing process to begin. During the healing process, damaged cells capable of proliferation regenerate. Tissue repair, resulting in <a href=\"https:\/\/www.britannica.com\/science\/scar\">scar<\/a> formation, may occur when normal tissue architecture cannot be regenerated successfully. Failure to replicate the original framework of an organ can lead to disease. Acute inflammation is usually beneficial but often causes unpleasant sensations, such as pain or itching. In some instances inflammation can cause harm. Tissue destruction can occur when the regulatory mechanisms of the inflammatory response are defective or the ability to clear damaged tissue and foreign substances is impaired. In other cases an inappropriate immune response may give rise to a prolonged and damaging inflammatory response. In <a href=\"https:\/\/www.britannica.com\/science\/autoimmunity\">autoimmune<\/a> reactions, the body\u2019s immune system attacks its own tissues, leading to long-term chronic inflammation. " } } ] } </script> <div class="top-questions qa-accordion d-flex flex-column module-spacing"><div class="font-weight-bold font-14 mb-5"> Top Questions </div><div id="intent-accordion" class="md-intent-accordion"><div class="top-question bg-gray-50 rounded" data-value="1"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>What is inflammation? </div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>Inflammation is a response triggered by damage to living <a href="https://www.britannica.com/science/tissue" class="md-crosslink " data-show-preview="true">tissues</a>. The inflammatory response is a defense mechanism that evolved in higher organisms to protect them from infection and <a href="https://www.britannica.com/science/wound" class="md-crosslink " data-show-preview="true">injury</a>. Its purpose is to localize and eliminate the injurious agent and to remove damaged tissue components so that the body can begin to heal. The response consists of changes in blood flow, an increase in permeability of blood vessels, and the migration of fluid, proteins, and white blood cells (<a href="https://www.britannica.com/science/white-blood-cell" class="md-crosslink " data-show-preview="true">leukocytes</a>) from the circulation to the site of tissue damage. An inflammatory response that lasts only a few days is called acute inflammation, while a response of longer duration is referred to as chronic inflammation. </p></div><div class="connections border-top mt-15"><a href="/story/how-is-inflammation-involved-in-swelling" class="d-flex mt-15">How Is Inflammation Involved in Swelling?</a>Learn more about how inflammation is involved in swelling.</div></div></div><div class="top-question bg-gray-50 rounded" data-value="2"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>What are the signs of inflammation? </div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>The four cardinal signs of inflammation are redness (Latin <em>rubor</em>), heat (<em>calor</em>), swelling (<em>tumor</em>), and pain (<em>dolor</em>).</p><ul class="bullet"><li>Redness is caused by the dilation of small blood vessels in the area of injury.</li><li>Heat results from increased blood flow through the area and is experienced only in peripheral parts of the body such as the skin. <a href="https://www.britannica.com/science/fever" class="md-crosslink bullet" data-show-preview="true">Fever</a> is brought about by chemical mediators of inflammation and contributes to the rise in temperature at the injury.</li><li>Swelling, called <a href="https://www.britannica.com/science/edema" class="md-crosslink bullet" data-show-preview="true">edema</a>, is caused primarily by the accumulation of fluid outside the blood vessels.</li><li>The pain associated with inflammation results in part from the distortion of tissues caused by edema, and it also is induced by certain chemical mediators of inflammation, such as bradykinin, <a href="https://www.britannica.com/science/serotonin" class="md-crosslink bullet" data-show-preview="true">serotonin</a>, and the <a href="https://www.britannica.com/science/prostaglandin" class="md-crosslink bullet" data-show-preview="true">prostaglandins</a>.</li></ul><div class="continue-reading"> Read more below: <a href="/science/inflammation#ref214901">Signs</a></div></div></div></div><div class="top-question bg-gray-50 rounded" data-value="3"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>Is inflammation good or bad? </div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>Inflammation serves as a defense mechanism against infection and injury, and localizing and eliminating injurious factors and removing damaged <a href="https://www.britannica.com/science/tissue" class="md-crosslink " data-show-preview="true">tissue</a> components allows the healing process to begin. During the healing process, damaged cells capable of proliferation regenerate. Tissue repair, resulting in <a href="https://www.britannica.com/science/scar" class="md-crosslink " data-show-preview="true">scar</a> formation, may occur when normal tissue architecture cannot be regenerated successfully. Failure to replicate the original framework of an organ can lead to disease. Acute inflammation is usually beneficial but often causes unpleasant sensations, such as pain or itching. In some instances inflammation can cause harm. Tissue destruction can occur when the regulatory mechanisms of the inflammatory response are defective or the ability to clear damaged tissue and foreign substances is impaired. In other cases an inappropriate immune response may give rise to a prolonged and damaging inflammatory response. In <a href="https://www.britannica.com/science/autoimmunity" class="md-crosslink " data-show-preview="true">autoimmune</a> reactions, the body’s immune system attacks its own tissues, leading to long-term chronic inflammation. </p></div></div></div></div></div><div class="bg-gray-50 p-15 rounded module-spacing recent-news d-flex flex-column float-false"> <div> <h2 class="font-weight-bold font-14 m-0 d-inline"> News <span class="text-gray-600">•</span> </h2> <div class="recent-news-item first-recent-news-item d-inline"> <a class="font-14 gtm-ap-news-link" href="https://medicalxpress.com/news/2024-11-mouse-females-quickly-males-muscle.html" rel="nofollow">Mouse study finds females heal more quickly than males after muscle injuries, with less inflammation and scar tissue</a> <span class="font-14 text-gray-600"> <span>•</span> Nov. 22, 2024, 12:10 AM ET (Medical Xpress) <button class="btn btn-link d-inline p-0 font-12 js-toggle-recent-news"> <span class="text-gray-500">...</span><span>(Show more)</span> </button> </span> </div> </div> <div class="rest-of-recent-news-items"> <div class="recent-news-item mt-5"> <a class="font-14 gtm-ap-news-link" href="https://medicalxpress.com/news/2024-11-air-pollution-inflammation-primarily-patients.html" rel="nofollow">New study finds air pollution increases inflammation primarily in patients with heart disease</a> <span class="font-14 text-gray-600"> <span>•</span> Nov. 18, 2024, 9:52 PM ET (Medical Xpress) </span> </div> <div class="recent-news-item mt-5"> <a class="font-14 gtm-ap-news-link" href="https://medicalxpress.com/news/2024-10-covid-inflammation-heart-blood-analysis.html" rel="nofollow">Long COVID inflammation damages the heart, blood analysis finds</a> <span class="font-14 text-gray-600"> <span>•</span> Oct. 31, 2024, 6:05 AM ET (Medical Xpress) </span> </div> <button class="js-toggle-recent-news d-flex btn btn-unstyled font-14 pr-10 rounded-sm mt-10" aria-label="Toggle additional news items"> Show less <em class="material-icons" data-icon="expand_less"></em> </button> </div> </div><span class="marker before-article"></span><section data-level="1" id="ref1"><span class="marker PREMOD1 mod-inline"></span><p class="topic-paragraph"><strong><span id="ref708735"></span>inflammation</strong>, a response triggered by damage to living <span id="ref708736"></span><a href="https://www.britannica.com/science/tissue" class="md-crosslink " data-show-preview="true">tissues</a>. The inflammatory response is a <a href="https://www.britannica.com/topic/defense-mechanism" class="md-crosslink autoxref " data-show-preview="true">defense mechanism</a> that evolved in higher organisms to protect them from <span id="ref1255544"></span><a href="https://www.britannica.com/science/infection" class="md-crosslink ">infection</a> and <span id="ref708901"></span><a href="https://www.britannica.com/science/wound" class="md-crosslink " data-show-preview="true">injury</a>. Its purpose is to localize and eliminate the injurious agent and to remove damaged tissue components so that the body can begin to heal. The response consists of changes in <a href="https://www.britannica.com/science/blood-biochemistry" class="md-crosslink " data-show-preview="true">blood</a> flow, an increase in permeability of <a href="https://www.britannica.com/science/blood-vessel" class="md-crosslink " data-show-preview="true">blood vessels</a>, and the migration of fluid, <a href="https://www.britannica.com/science/protein" class="md-crosslink " data-show-preview="true">proteins</a>, and <a href="https://www.britannica.com/science/white-blood-cell" class="md-crosslink " data-show-preview="true">white blood cells</a> (leukocytes) from the <a href="https://www.britannica.com/science/circulation-anatomy-and-physiology" class="md-crosslink autoxref " data-show-preview="true">circulation</a> to the site of tissue damage. An inflammatory response that lasts only a few days is called <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="acute" href="https://www.merriam-webster.com/dictionary/acute" data-type="MW">acute</a> inflammation, while a response of longer duration is referred to as chronic inflammation.</p><span class="marker MOD1 mod-inline"></span><span class="marker PREMOD2 mod-inline"></span><p class="topic-paragraph">Although <span id="ref1255051"></span>acute inflammation is usually <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="beneficial" href="https://www.merriam-webster.com/dictionary/beneficial" data-type="MW">beneficial</a>, it often causes unpleasant sensations, such as the <a href="https://www.britannica.com/science/pain" class="md-crosslink " data-show-preview="true">pain</a> of a <a href="https://www.britannica.com/science/sore-throat" class="md-crosslink autoxref " data-show-preview="true">sore throat</a> or the <a href="https://www.britannica.com/science/itching" class="md-crosslink " data-show-preview="true">itching</a> of an <a href="https://www.britannica.com/science/insect-bite-and-sting" class="md-crosslink " data-show-preview="true">insect bite</a>. Discomfort is usually temporary and disappears when the inflammatory response has done its job. But in some instances inflammation can cause harm. Tissue destruction can occur when the regulatory mechanisms of the inflammatory response are defective or the ability to clear damaged tissue and foreign substances is impaired. In other cases an inappropriate immune response may give rise to a prolonged and damaging inflammatory response. Examples include <span id="ref708982"></span><a href="https://www.britannica.com/science/immune-system-disorder/Deficiencies-caused-by-malnutrition#ref215500" class="md-crosslink " data-show-preview="true">allergic</a>, or <a href="https://www.britannica.com/science/allergy" class="md-crosslink autoxref " data-show-preview="true">hypersensitivity</a>, reactions, in which an environmental agent such as <a href="https://www.britannica.com/science/pollen" class="md-crosslink " data-show-preview="true">pollen</a>, which normally poses no threat to the individual, <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="stimulates" href="https://www.britannica.com/dictionary/stimulates" data-type="EB">stimulates</a> inflammation, and <span id="ref1254527"></span><a href="https://www.britannica.com/science/autoimmunity" class="md-crosslink " data-show-preview="true">autoimmune reactions</a>, in which chronic inflammation is triggered by the body’s immune response against its own tissues.</p><span class="marker MOD2 mod-inline"></span></section> <span class="marker h2"></span><section data-level="1" id="ref214900"> <h2 class="h1">Causes</h2> <span class="marker PREMOD3 mod-inline"></span><p class="topic-paragraph">The factors that can stimulate inflammation include microorganisms, physical agents, chemicals, inappropriate immunological responses, and tissue death. Infectious agents such as <a href="https://www.britannica.com/science/virus" class="md-crosslink " data-show-preview="true">viruses</a> and <a href="https://www.britannica.com/science/bacteria" class="md-crosslink " data-show-preview="true">bacteria</a> are some of the most common stimuli of inflammation. Viruses give rise to inflammation by entering and destroying cells of the body; bacteria release substances called <a href="https://www.britannica.com/science/endotoxin" class="md-crosslink " data-show-preview="true">endotoxins</a> that can initiate inflammation. Physical trauma, <a href="https://www.britannica.com/science/burn" class="md-crosslink " data-show-preview="true">burns</a>, <a href="https://www.britannica.com/science/radiation-injury" class="md-crosslink " data-show-preview="true">radiation injury</a>, and <a href="https://www.britannica.com/science/frostbite" class="md-crosslink " data-show-preview="true">frostbite</a> can damage tissues and also bring about inflammation, as can corrosive chemicals such as acids, alkalis, and oxidizing agents. As mentioned above, malfunctioning immunological responses can incite an inappropriate and damaging inflammatory response. Inflammation can also result when tissues die from a lack of oxygen or nutrients, a situation that often is caused by loss of blood flow to the area.</p><span class="marker MOD3 mod-inline"></span> </section> <span class="marker h3"></span><section data-level="1" id="ref214901"> <h2 class="h1">Signs</h2> <span class="marker PREMOD4 mod-inline"></span><p class="topic-paragraph">The four cardinal signs of inflammation—redness (Latin <em>rubor</em>), <a href="https://www.britannica.com/science/heat" class="md-crosslink autoxref " data-show-preview="true">heat</a> (<em>calor</em>), swelling (<em>tumor</em>), and pain (<em>dolor</em>)—were described in the 1st century <span class="text-smallcaps">ad</span> by the Roman medical writer <span id="ref708897"></span><a href="https://www.britannica.com/biography/Aulus-Cornelius-Celsus" class="md-crosslink " data-show-preview="true">Aulus Cornelius Celsus</a>. Redness is caused by the dilation of small blood vessels in the area of injury. Heat results from increased blood flow through the area and is experienced only in <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="peripheral" href="https://www.merriam-webster.com/dictionary/peripheral" data-type="MW">peripheral</a> parts of the body such as the skin. Fever is brought about by chemical mediators of inflammation and contributes to the rise in temperature at the injury. Swelling, called <span id="ref708898"></span><a href="https://www.britannica.com/science/edema" class="md-crosslink " data-show-preview="true">edema</a>, is caused primarily by the accumulation of fluid outside the blood vessels. The pain associated with inflammation results in part from the distortion of tissues caused by edema, and it also is induced by certain chemical mediators of inflammation, such as bradykinin, <a href="https://www.britannica.com/science/serotonin" class="md-crosslink " data-show-preview="true">serotonin</a>, and the <a href="https://www.britannica.com/science/prostaglandin" class="md-crosslink " data-show-preview="true">prostaglandins</a>.</p><span class="marker MOD4 mod-inline"></span> <span class="marker PREMOD5 mod-inline"></span><p class="topic-paragraph">A fifth consequence of inflammation is the loss of function of the inflamed area, a feature noted by German pathologist <a href="https://www.britannica.com/biography/Rudolf-Virchow" class="md-crosslink " data-show-preview="true">Rudolf Virchow</a> in the 19th century. Loss of function may result from pain that <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="inhibits" href="https://www.merriam-webster.com/dictionary/inhibits" data-type="MW">inhibits</a> mobility or from severe swelling that prevents movement in the area.</p><a class="link-module shadow-sm d-block qa-quiz-module" href="/quiz/diseases-disorders-and-more-a-medical-quiz" data-link-module-iframe-link=""> <img loading="lazy" src="https://cdn.britannica.com/15/93315-131-EA8F7ABF/human-skeleton-framework-body-organs-protection-range.jpg" alt="full human skeleton" class="rounded-sm mr-15" width="70" /> <div class="line-clamp clamp-5"> <div class="module-title bg-green">Britannica Quiz</div> <div class="font-weight-semi-bold mt-5">Diseases, Disorders, and More: A Medical Quiz</div> </div> </a><span class="marker MOD5 mod-inline"></span> </section> <span class="marker h4"></span><section data-level="1" id="ref214902"> <h2 class="h1">The acute inflammatory response</h2> <section data-level="2" id="ref214903"> <h2 class="h2">Vascular changes</h2> <span class="marker PREMOD6 mod-inline"></span><p class="topic-paragraph">When tissue is first injured, the small blood vessels in the damaged area constrict momentarily, a process called vasoconstriction. Following this <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="transient" href="https://www.merriam-webster.com/dictionary/transient" data-type="MW">transient</a> event, which is believed to be of little importance to the inflammatory response, the blood vessels dilate (<span id="ref708983"></span><a href="https://www.britannica.com/science/vasodilation" class="md-crosslink ">vasodilation</a>), increasing blood flow into the area. Vasodilation may last from 15 minutes to several hours.</p><span class="marker MOD6 mod-inline"></span> <span class="marker PREMOD7 mod-inline"></span><p class="topic-paragraph">Next, the walls of the blood vessels, which normally allow only water and salts to pass through easily, become more permeable. Protein-rich fluid, called <span id="ref1255550"></span>exudate, is now able to exit into the tissues. Substances in the exudate include <a href="https://www.britannica.com/science/coagulation-of-blood" class="md-crosslink autoxref " data-show-preview="true">clotting</a> factors, which help prevent the spread of infectious agents throughout the body. Other proteins include antibodies that help destroy invading microorganisms.</p><div class="module-spacing"> <DIV class="marketing-INLINE_SUBSCRIPTION marketing-content" data-marketing-id="INLINE_SUBSCRIPTION"><style> .student-promo-banner-wrapper { container-type: inline-size; margin-bottom: 15px; } @container (min-width: 475px) { .student-promo-banner { flex-direction: row; } .student-promo-banner-img-wrapper { margin-bottom: 0; margin-right: 10px; justify-content: flex-start; } .student-promo-banner-text-wrapper { text-align: left; margin-bottom: 0px; margin-left: 10px; } .student-promo-banner-button-wrapper { margin-right: 0; } }</style> <div class="student-promo-banner-wrapper"> <div class="student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20"> <div class="student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center"> <img class="rounded" style="max-width: 100px; min-width: 80px" src="https://cdn.britannica.com/marketing/BlueThistle.webp" /> </div> <div class="student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white"> <div class="h2 mb-10">Get Unlimited Access</div> <div class="h4 font-weight-semi-bold">Try Britannica Premium for free and discover more.</div> </div> <div class="student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto"> <a class="btn btn-m btn-orange" href="https://premium.britannica.com/premium-membership/?utm_source=premium&utm_medium=inline-cta&utm_campaign=black-friday-2024">Subscribe</a> </div> </div> </div> </DIV></div><div class="one-good-fact-module"> </div><span class="marker MOD7 mod-inline"></span> <span class="marker PREMOD8 mod-inline"></span><p class="topic-paragraph">As fluid and other substances leak out of the blood <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="vessels" href="https://www.britannica.com/dictionary/vessels" data-type="EB">vessels</a>, blood flow becomes more sluggish and <span id="ref708903"></span><a href="https://www.britannica.com/science/white-blood-cell" class="md-crosslink " data-show-preview="true">white blood cells </a>begin to fall out of the axial stream in the centre of the vessel to flow nearer the vessel wall. 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Inflammation | Definition, Symptoms, Treatment, & Facts | Britannica