question: Why is 100 degrees Fahrenheit considered the starting point of a fever? Is it just an easy number that is approximately where symptoms start?
comment: 98.6 degrees F is the human average. Indeed, 99 degrees is usually considered the beginning of a fever and anything over 100 degrees is certainly a fever. This of course varies from person to person so it cannot be applied to every human. Much lower than 98.6 degrees and you're prolly dead, right 💁‍♂️
passages: A temperature "setpoint" is the level at which the body attempts to maintain its temperature. When the setpoint is raised, the result is a fever. Most fevers are caused by infectious disease and can be lowered, if desired, with antipyretic medications.
  
  An early morning temperature higher than or a late afternoon temperature higher than is normally considered a fever, assuming that the temperature is elevated due to a change in the hypothalamus's setpoint. Lower thresholds are sometimes appropriate for elderly people. The normal daily temperature variation is typically , but can be greater among people recovering from a fever.
   In healthy adults, the range of normal, healthy temperatures for oral temperature is , for rectal it is , for tympanic membrane (the ear drum) it is , and for axillary (the armpit) it is . Harrison's Principles of Internal Medicine defines a fever as a morning oral temperature of 37.2 °C (98.9 °F) or an afternoon oral temperature of 37.7 °C (99.9 °F) while the normal daily temperature variation is typically 0.5 °C (0.9 °F).
   A wide range for normal temperatures has been found. Central temperatures, such as rectal temperatures, are more accurate than peripheral temperatures.
  
  Fever is generally agreed to be present if the elevated temperature is caused by a raised set point and:
  
  BULLET::::- Temperature in the anus (rectum/rectal) is at or over
  
  BULLET::::- Temperature in the mouth (oral) is at or over
  
  BULLET::::- Temperature under the arm (axillary) or in the ear (tympanic) is at or over
   Remittent fever
  
  Remittent Fever is a type or pattern of fever in which temperature does not touch the baseline and remains above normal throughout the day. Daily variation in temperature is more than 1°C in 24 hours, which is also the main difference as compared to continuous fever. Fever due to most infectious diseases is remittent. Diagnosis is based upon clinical history, blood tests, blood culture and chest X-ray.
  
  Section::::Examples.
  
  Examples of remittent fever are as following.
  
  BULLET::::- Infective endocarditis
  
  BULLET::::- Typhoid
  
  BULLET::::- Brucellosis
  
  Section::::Management.
   Continuous fever
  
  Continuous fever is a type or pattern of fever in which temperature does not touch the baseline and remains above normal throughout the day. The variation between maximum and minimum temperature in 24 hours is less than 1°C (1.5°F). It usually occurs due to some infectious disease. Diagnosis of continuous fever is usually based on the clinical signs and symptoms but some biological tests, chest X-ray and CT scan are also used. Typhoid fever is an example of continuous fever and it shows a characteristic step-ladder pattern, a step-wise increase in temperature with a high plateau.
  
  Section::::Examples.
   Fever, also known as pyrexia and febrile response, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using values between . The increase in set point triggers increased muscle contractions and causes a feeling of cold. This results in greater heat production and efforts to conserve heat. When the set point temperature returns to normal, a person feels hot, becomes flushed, and may begin to sweat. Rarely a fever may trigger a febrile seizure. This is more common in young children. Fevers do not typically go higher than .
   Normal body temperatures vary depending on many factors, including age, sex, time of day, ambient temperature, activity level, and more. A raised temperature is not always a fever. For example, the temperature of a healthy person rises when he or she exercises, but this is not considered a fever, as the set point is normal. On the other hand, a "normal" temperature may be a fever, if it is unusually high for that person. For example, medically frail elderly people have a decreased ability to generate body heat, so a "normal" temperature of may represent a clinically significant fever.
  
  Section::::Diagnosis.:Types.
   Despite all this, diagnosis may only be suggested by the therapy chosen. When a patient recovers after discontinuing medication it likely was drug fever, when antibiotics or antimycotics work it probably was infection. Empirical therapeutic trials should be used in those patients in which other techniques have failed.
  
  Section::::Diagnosis.:Definition.
  
  In 1961 Petersdorf and Beeson suggested the following criteria:
  
  BULLET::::- Fever higher than 38.3 °C (101 °F) on several occasions
  
  BULLET::::- Persisting without diagnosis for at least 3 weeks
  
  BULLET::::- At least 1 week's investigation in hospital
  
  A new definition which includes the outpatient setting (which reflects current medical practice) is broader, stipulating:
   Clinical phases of Marburg Hemorrhagic Fever's presentation are described below. Note that phases overlap due to variability between cases.
  
  BULLET::::1. Incubation: 2–21 days, averaging 5–9 days.
  
  BULLET::::2. Generalization Phase: Day 1 up to Day 5 from onset of clinical symptoms. MHF presents with a high fever 104 °F (~40˚C) and a sudden, severe headache, with accompanying chills, fatigue, nausea, vomiting, diarrhea, pharyngitis, maculopapular rash, abdominal pain, conjunctivitis, & malaise.
   BULLET::::- Exaggerated circadian rhythm
  
  Section::::Causes.:Other.
  
  BULLET::::- “Afebrile” FUO [38.3 °C (100.94 °F)]
  
  Section::::Diagnosis.
  
  A comprehensive and meticulous history (i.e. illness of family members, recent visit to the tropics, medication), repeated physical examination (i.e. skin rash, eschar, lymphadenopathy, heart murmur) and myriad laboratory tests (serological, blood culture, immunological) are the cornerstone of finding the cause.
   Temperature can be recorded in order to establish a baseline for the individual's normal body temperature for the site and measuring conditions. The main reason for checking body temperature is to solicit any signs of systemic infection or inflammation in the presence of a fever (temp  38.5 °C/101.3 °F or sustained temp  38 °C/100.4 °F), or elevated significantly above the individual's normal temperature. Other causes of elevated temperature include hyperthermia.
   Temperature depression (hypothermia) also needs to be evaluated. It is also noteworthy to review the trend of the patient's temperature. A fever of 38 °C is not necessarily indicate an ominous sign if the patient's previous temperature has been higher.
  
  Section::::Primary vital signs.:Pulse.
   In documented BPF cases, the symptoms include high fever (101.3 °F/38,5 °C or higher), nausea, vomiting, severe abdominal pain, septic shock, and ultimately death. A history of conjunctivitis 30 days prior to the onset of fever was also present in the documented BPF cases.
   With fever, the body's core temperature rises to a higher temperature through the action of the part of the brain that controls the body temperature; with hyperthermia, the body temperature is raised without the influence of the heat control centers.
  
  Section::::Concepts.:Hypothermia.
  
  In hypothermia, body temperature drops below that required for normal metabolism and bodily functions. In humans, this is usually due to excessive exposure to cold air or water, but it can be deliberately induced as a medical treatment. Symptoms usually appear when the body's core temperature drops by below normal temperature.
  
  Section::::Concepts.:Basal body temperature.
   BULLET::::5. Botanical, and plant pathology. Poisoning, or infecting, plants with the help of bacteria.
  
  BULLET::::6. Preparations for bacteriological warfare
  
  Section::::Mission.
   Fever is an important feature for the diagnosis of disease in domestic animals. The body temperature of animals, which is taken rectally, is different from one species to another. For example, a horse is said to have a fever above (). In species that allow the body to have a wide range of "normal" temperatures, such as camels, it is sometimes difficult to determine a febrile stage.
   It is important to note that similar calculations may be carried out to determine "accumulated degree minutes," "accumulated degree seconds," etc., though ADD and ADH are typically used in forensic analyses.
  
  For "S. bullata", the following temperature data has been determined in a laboratory setting. These calculations correspond to a standardized temperature of 27 °C.
  
  Section::::Other research.
   A number of types of fever were known as early as 460 BC to 370 BC when Hippocrates was practicing medicine including that due to malaria (tertian or every 2 days and quartan or every 3 days). It also became clear around this time that fever was a symptom of disease rather than a disease in and of itself.
  
  Section::::Society and culture.
  
  Section::::Society and culture.:Etymology.
  
  Pyrexia is from the Greek "pyr" meaning "fire". Febrile is from the Latin word "febris", meaning "fever", and archaically known as "ague".
  
  Section::::Society and culture.:Fever phobia.
   Other investigations may be needed. Ultrasound may show cholelithiasis, echocardiography may be needed in suspected endocarditis and a CT-scan may show infection or malignancy of internal organs. Another technique is Gallium-67 scanning which seems to visualize chronic infections more effectively. Invasive techniques (biopsy and laparotomy for pathological and bacteriological examination) may be required before a definite diagnosis is possible.
  
  Positron emission tomography using radioactively labelled fluorodeoxyglucose (FDG) has been reported to have a sensitivity of 84% and a specificity of 86% for localizing the source of fever of unknown origin.
   Professor Carl Braun in Vienna said about the Copenhagen hospital, that "because this is the most appropriate and noteworthy newly constructed maternity hospital, in which every step has been taken to halt puerperal fever epidemics, we allow ourselves to estimate that in this new building under Levy's direction no puerperal fever epidemics will occur."
   It is difficult to clinically exclude sepsis in newborns less than 90 days old that have fever (defined as a temperature  38 °C (100.4 °F). Except in the case of obvious acute viral bronchiolitis, the current practice in newborns less than 30 days old is to perform a complete workup including complete blood count with differential, blood culture, urinalysis, urine culture, and cerebrospinal fluid (CSF) studies and CSF culture, admit the newborn to the hospital, and treat empirically for serious bacterial infection for at least 48 hours until cultures are demonstrated to show no growth. Attempts have been made to see whether it is possible to risk stratify newborns in order to decide if a newborn can be safely monitored at home without treatment despite having a fever. One such attempt is the Rochester criteria.
   In the 19th century, most books quoted "blood heat" as 98 °F, until a study published the mean (but not the variance) of a large sample as . Subsequently that mean was widely quoted as "37 °C or 98.4 °F" until editors realised 37 °C is closer to 98.6 °F than 98.4 °F. The 37 °C value was set by German physician Carl Reinhold August Wunderlich in his 1868 book, which put temperature charts into widespread clinical use. Dictionaries and other sources that quoted these averages did add the word "about" to show that there is some variance, but generally did not state how wide the variance is.
   Section::::Diagnosis.
  
  Hyperthermia is generally diagnosed by the combination of unexpectedly high body temperature and a history that supports hyperthermia instead of a fever. Most commonly this means that the elevated temperature has occurred in a hot, humid environment (heat stroke) or in someone taking a drug for which hyperthermia is a known side effect (drug-induced hyperthermia). The presence of signs and symptoms related to hyperthermia syndromes, such as extrapyramidal symptoms characteristic of neuroleptic malignant syndrome, and the absence of signs and symptoms more commonly related to infection-related fevers, are also considered in making the diagnosis.
   Laboratory testing and imaging is generally deferred for evaluation of fever that occurs within the first 48 hours post-operatively, unless prompted by specific findings in the history and physical exam. Beyond 48 hours, testing routinely includes urine and blood cultures as well as a chest X-ray.
  
  Section::::Popular culture.
  
  In the pilot episode of the medical drama "Grey's Anatomy", Meredith Grey refers to this mnemonic: "Wind, water, wound, walking, wonder drugs. The 5 Ws. Most of the time it’s wind; splinting or pneumonia. Pneumonia is easy to assume. Especially if you're too busy to do the tests." 
  
  Section::::See also.
   "Febricula" is an old term for a low-grade fever, especially if the cause is unknown, no other symptoms are present, and the patient recovers fully in less than a week.
  
  Section::::Diagnosis.:Hyperpyrexia.
  
presuppositions: 100 degrees Fahrenheit considered the starting point of a fever. 100 degres fahrenheit is the starting point of a fever.
corrections: 99 degrees Fahrenheit considered the starting point of a fever. 99 degrees is considered the beginning of a fever.
raw_presuppositions: 100 degrees Fahrenheit considered the starting point of a fever. 100 degres fahrenheit is the starting point of a fever.
raw_corrections: 99 degrees Fahrenheit considered the starting point of a fever. 99 degrees is considered the beginning of a fever.