{"id":6550,"date":"2026-06-03T13:47:07","date_gmt":"2026-06-03T17:47:07","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/?post_type=chapter&p=6550"},"modified":"2026-06-10T15:48:28","modified_gmt":"2026-06-10T19:48:28","slug":"fever","status":"web-only","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/chapter\/fever\/","title":{"raw":"Section 5:\u00a0 Fever","rendered":"Section 5:\u00a0 Fever"},"content":{"raw":"

A rise in body temperature above 37.2\u00b0C is called a fever,<\/strong> caused by pyrogens<\/strong> released in response to cellular damage or irritation.\u00a0 A low-grade fever (38-39\u00b0C)<\/strong> is a beneficial innate response - it accelerates WBC activity, inhibits pathogen metabolism and replication, and speeds healing.<\/p>\r\n\r\n\r\n\r\n\r\n\r\n
Endogenous pyrogens<\/strong><\/span><\/td>\r\nProduced by WBCs (e.g., interferons<\/strong> and interleukins).<\/strong>\r\n\r\nStimulate the thermoregulation center in the hypothalamus to raise the body's temperature set point.<\/td>\r\n<\/tr>\r\n
Exogenous pyrogens<\/strong><\/span><\/td>\r\nForeign components (e.g., LPS<\/strong> - lipopolysaccharides from bacterial cell walls) that also trigger fever.<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n[caption id=\"attachment_6791\" align=\"alignnone\" width=\"300\"]\"The<\/a> The role of the hypothalamus in the inflammatory response, fever. The activation of leukocytes during an infection or injury can result in the release of endogenous pyrogens (e.g., a set of cytokines including specific interleukins) which trigger the production of prostaglandin E2 (PGE2) which resets the hypothalamus, the body's thermostat, to initiate fever. Gram-negative bacteria have lipopolysaccharide (LPS) capsule, which is considered an endotoxin and an exogenous pyrogen, which causes WBCs to produce more of these pyrogens. Some pathogens can lead to high levels of pyrogens being released which can cause dangerously high spiking fevers.[\/caption]\r\n

The Four Stages of Fever<\/strong><\/span><\/h3>\r\n\r\n\r\n\r\n\r\n\r\n\r\n
1.\u00a0 Prodromal<\/strong><\/span><\/td>\r\nOnset stage - beginning to feel unwell;\u00a0 pyrogens start circulating<\/td>\r\n<\/tr>\r\n
2.\u00a0 Chills<\/strong><\/span><\/td>\r\nPyrogens<\/strong> reset the hypothalamic thermostat<\/strong> to a higher level (e.g., 39\u00b0C).\u00a0 Because the body is not yet at 39\u00b0C, you feel cold and shiver despite already being warm.\u00a0 <\/span>\r\n\r\nThe body raises temperature through <\/span>shivering,<\/strong> erector pili muscle contraction<\/strong> (form goosebumps and generate heat), and increasing heart rate<\/strong>, and\u00a0basal metabolic rate (BMR)<\/strong>.\u00a0\u00a0\u00a0<\/span>\r\n\r\nSkin pallor as <\/span>cutaneous vasoconstriction<\/strong> occurs<\/span> to reduce heat loss.\u00a0\u00a0<\/span>\r\n\r\nBehavioural changes (layering clothing, blankets) also occur.<\/td>\r\n<\/tr>\r\n
3.\u00a0 Flush<\/strong><\/span><\/td>\r\nBody temperature is at or above 37.2\u00b0C.\u00a0 Remains in this stage as long as pyrogens continue stimulating the hypothalamus.<\/td>\r\n<\/tr>\r\n
4.\u00a0 Defervescence (Sweating)<\/strong><\/span><\/td>\r\nInfection resolves; pyrogens diminish; hypothalamus resets to 37\u00b0C.\r\n\r\nThe body cools by:\u00a0 (a) vasodilating<\/strong> cutaneous vessels to radiate heat; (b) sweating;<\/strong> (c) reducing BMR and heart rate; (d) reducing movement; and (e) removing extra clothing and blankets.<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n
\r\n

High Fever and Its Dangers<\/strong><\/p>\r\n\r\n<\/header>\r\n

\r\n

A spiking fever of 40\u00b0C or above can cause febrile seizures<\/strong> (putting the brain at risk for neural damage) and is also characteristic of heat stroke<\/strong> (inability to thermoregulate and cool the body).<\/p>\r\n

Febrile seizure treatment<\/strong> involves placing the child on a soft flat surface away from sharp objects, while keeping mouth clear of objects and timing the seizure's duration.<\/p>\r\n

Both febrile seizures and heat stroke can quickly evolve to become medical emergencies<\/strong> and should involve calling 9-1-1.<\/p>\r\n

Heat stroke treatment<\/strong> should involve cooling the person as quickly as possible by moving them to a cooler area, and using cold water and ice packs, as well as providing cool water to drink.<\/p>\r\n

A blunted or absent febrile response<\/strong> in the elderly or immunosuppressed may delay diagnosis and treatment, making clinical assessment more challenging.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n

<\/h3>","rendered":"

A rise in body temperature above 37.2\u00b0C is called a fever,<\/strong> caused by pyrogens<\/strong> released in response to cellular damage or irritation.\u00a0 A low-grade fever (38-39\u00b0C)<\/strong> is a beneficial innate response – it accelerates WBC activity, inhibits pathogen metabolism and replication, and speeds healing.<\/p>\n\n\n\n\n
Endogenous pyrogens<\/strong><\/span><\/td>\nProduced by WBCs (e.g., interferons<\/strong> and interleukins).<\/strong><\/p>\n

Stimulate the thermoregulation center in the hypothalamus to raise the body’s temperature set point.<\/td>\n<\/tr>\n

Exogenous pyrogens<\/strong><\/span><\/td>\nForeign components (e.g., LPS<\/strong> – lipopolysaccharides from bacterial cell walls) that also trigger fever.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\"The<\/a>
The role of the hypothalamus in the inflammatory response, fever. The activation of leukocytes during an infection or injury can result in the release of endogenous pyrogens (e.g., a set of cytokines including specific interleukins) which trigger the production of prostaglandin E2 (PGE2) which resets the hypothalamus, the body’s thermostat, to initiate fever. Gram-negative bacteria have lipopolysaccharide (LPS) capsule, which is considered an endotoxin and an exogenous pyrogen, which causes WBCs to produce more of these pyrogens. Some pathogens can lead to high levels of pyrogens being released which can cause dangerously high spiking fevers.<\/figcaption><\/figure>\n

The Four Stages of Fever<\/strong><\/span><\/h3>\n\n\n\n\n\n\n
1.\u00a0 Prodromal<\/strong><\/span><\/td>\nOnset stage – beginning to feel unwell;\u00a0 pyrogens start circulating<\/td>\n<\/tr>\n
2.\u00a0 Chills<\/strong><\/span><\/td>\nPyrogens<\/strong> reset the hypothalamic thermostat<\/strong> to a higher level (e.g., 39\u00b0C).\u00a0 Because the body is not yet at 39\u00b0C, you feel cold and shiver despite already being warm.\u00a0 <\/span><\/p>\n

The body raises temperature through <\/span>shivering,<\/strong> erector pili muscle contraction<\/strong> (form goosebumps and generate heat), and increasing heart rate<\/strong>, and\u00a0basal metabolic rate (BMR)<\/strong>.\u00a0\u00a0\u00a0<\/span><\/p>\n

Skin pallor as <\/span>cutaneous vasoconstriction<\/strong> occurs<\/span> to reduce heat loss.\u00a0\u00a0<\/span><\/p>\n

Behavioural changes (layering clothing, blankets) also occur.<\/td>\n<\/tr>\n

3.\u00a0 Flush<\/strong><\/span><\/td>\nBody temperature is at or above 37.2\u00b0C.\u00a0 Remains in this stage as long as pyrogens continue stimulating the hypothalamus.<\/td>\n<\/tr>\n
4.\u00a0 Defervescence (Sweating)<\/strong><\/span><\/td>\nInfection resolves; pyrogens diminish; hypothalamus resets to 37\u00b0C.<\/p>\n

The body cools by:\u00a0 (a) vasodilating<\/strong> cutaneous vessels to radiate heat; (b) sweating;<\/strong> (c) reducing BMR and heart rate; (d) reducing movement; and (e) removing extra clothing and blankets.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\n
\n

High Fever and Its Dangers<\/strong><\/p>\n<\/header>\n

\n

A spiking fever of 40\u00b0C or above can cause febrile seizures<\/strong> (putting the brain at risk for neural damage) and is also characteristic of heat stroke<\/strong> (inability to thermoregulate and cool the body).<\/p>\n

Febrile seizure treatment<\/strong> involves placing the child on a soft flat surface away from sharp objects, while keeping mouth clear of objects and timing the seizure’s duration.<\/p>\n

Both febrile seizures and heat stroke can quickly evolve to become medical emergencies<\/strong> and should involve calling 9-1-1.<\/p>\n

Heat stroke treatment<\/strong> should involve cooling the person as quickly as possible by moving them to a cooler area, and using cold water and ice packs, as well as providing cool water to drink.<\/p>\n

A blunted or absent febrile response<\/strong> in the elderly or immunosuppressed may delay diagnosis and treatment, making clinical assessment more challenging.<\/p>\n<\/div>\n<\/div>\n

<\/h3>\n

Media Attributions<\/h2>