Body Parts: Whole Body
Medical Subjects: Children's Health

What Is Fever?

Fever, i.e. increased body temperature, is out of normal range.

The body temperature of normal people is regulated by the thermoregulatory center, which dynamically balances the heat production and dissipation processes through nervous and humoral factors, thus keeping the body temperature fluctuating within a relatively constant range (physiological range).

During the fever, the hypothalamic temperature setting was raised from normal to febrile, similar to resetting the indoor air conditioner to a higher temperature to raise the room temperature.

What is the normal body temperature of the human body?

The normal body temperature is generally around 36 C–37 C. The normal range of body temperature is slightly different with different measurement methods. Normal body temperature varies slightly among individuals, and is often slightly fluctuated under the influence of internal and external factors in the body.

In 24 hours, the body temperature in the afternoon is slightly higher than that in the morning, and it can also be slightly higher after strenuous exercise, work or eating, but the general fluctuation range is not more than 1℃.

The body temperature of women before menstruation and during pregnancy is slightly higher than normal. Due to low metabolic rate, the body temperature of the elderly is relatively lower than that of the young adults. In addition, the body temperature can also rise slightly under high temperature.

Is it a low-grade fever if the body temperature is lower than normal?

Temperature below the normal range (≤ 35℃) is not called low fever, the right should be called hypothermia or hypothermia, in shock, severe malnutrition, hypothyroidism, hypoglycemia coma, etc.

In addition, infantile hypothermia (35.1–36 C) for 1–2 days may occur during the recovery period after the infectious fever subsides, which is a normal phenomenon.



What Is The Cause Of Fever?

There are many causes of fever, which can be clinically divided into infectious and non-infectious categories, while the former are more common, in which the most common is viral or bacterial infection in the respiratory tract and gastrointestinal tract.

Infectious fever: Fever may occur due to infection caused by various pathogens such as viruses, bacteria, mycoplasma, rickettsia, spirochetes, fungi, and parasites, whether acute, subacute or chronic, local or systemic.

Acute infections: Fever < 2 weeks, common infectious factors include common influenza, respiratory infections (such as bronchitis), gastrointestinal infections, these infections are often not serious.

Chronic infection: Fever lasts for more than two weeks, and the common causes include tuberculosis, chronic pyelonephritis, chronic biliary infection, sinusitis, root abscess, prostatitis, chronic pelvic inflammatory disease, and perianal abscess.

Non-infectious fever: mainly due to the following causes:

  • Absorption of sterile necrotic substances: Fever may be caused by aseptic inflammation due to tissue cell necrosis, decomposition of tissue proteins, and absorption of tissue necrosis products, which are commonly found in:
  1. Mechanical, physical or chemical damage, such as heatstroke, tissue damage after major surgery, internal bleeding, large hematoma, fracture, large area burn and severe hypnotic poisoning, etc.; Intracranial diseases such as cerebral hemorrhage, cerebral concussion and cerebral contusion are central fever. Status epilepticus can cause fever, which is caused by excessive thermogenesis.
  2. Visceral infarction or limb necrosis of the myocardium, lung, and spleen caused by vascular embolism or thrombosis is usually called absorbed heat.
  3. Tissue necrosis and cell destruction such as cancer (malignant tumor), leukemia, lymphoma, hemolytic reaction, etc.
  • Antigen-antibody reaction: such as connective tissue diseases (systemic lupus erythematosus, dermatomyositis, scleroderma, rheumatoid arthritis and polyarteritis nodosa), allergic diseases (rheumatic fever, serum sickness, drug fever, hemolytic reaction), etc.
  • Endocrine and metabolic diseases: Such as hyperthyroidism, thyroiditis, gout and hypertonic dehydration.
  • Skin lesions: Extensive lesions of the skin cause fever due to reduced heat dissipation of the skin, which can be seen in extensive dermatitis, ichthyosis, etc. Chronic heart failure can also cause fever by reducing heat loss from the skin.
  • Autonomic nerve dysfunction: As a result of autonomic nerve dysfunction, the normal temperature regulation process is affected, resulting in greater heat production than heat dissipation, and increased body temperature, which is mostly low grade fever, often accompanied by other manifestations of autonomic nerve dysfunction, belonging to the category of functional fever. Common functional low heat are:
  • Primary low grade fever: It is due to thermoregulation disorder or constitutional abnormality caused by autonomic nerve dysfunction. The low grade fever can last for months or even years, with regular hot type and small fluctuation range of body temperature, most of which is within 0.5 C.
  • Low fever after infection cure: low fever does not return after fever caused by virus, bacteria, protozoa and other infections, while the original infection has been cured. This is due to the fact that the thermoregulatory function has not yet returned to normal, but it must be distinguished from fever caused by the activity of potential lesions (such as tuberculosis) or other new infections due to decreased body resistance.
  • Low grade fever in summer: low grade fever only occurs in summer, and it will reduce the fever after cooling in autumn. It recurs repeatedly every year and can be cured by oneself after several years. It is more common in infants because of the weakness in summer due to the imperfect function of thermoregulatory center, and it is more common in the patients with malnutrition or brain hypoplasia.
  • Physiological low grade fever: such as low grade fever after mental stress and strenuous exercise. Low fever may also occur before menstruation and in the first trimester of pregnancy.

What Is The Symptoms Of Fever?

How to classify fever?

According to the temperature, heating can be divided into (oral temperature):

  • Low heat: 37.3 ~ 38℃.
  • Moderate heat: 38.1–39℃.
  • High fever: 39–41℃.
  • Ultra-high fever: above 41℃.

However, it should be emphasized that the self-conscious discomfort of the human body during fever is more important than the degree of body temperature.

What is the difference between fever and overheating?

Fever needs to be distinguished from overheating.

Fever refers to the rise of the central body temperature set point, and the body temperature will rise accordingly.

Overheating means the human body temperature increases, but the central body temperature setting point does not increase. Similar to the air conditioner set at 26 c, but due to other effects, the ambient temperature exceeded this temperature.

Fever is regulated by the central nervous system, and the body temperature usually does not increase fatally. Therefore, antipyretics are effective.

However, the overheated body temperature rise is out of control. The body temperature rise far exceeds the heat dissipation ability, which can lead to dangerous high temperature in the body. The antipyretics are often ineffective and physical cooling is required.

Diseases that cause overheating through both exogenous heat exposure and endogenous heat production include heat stroke syndrome, certain metabolic diseases, and effects of drugs that interfere with thermoregulation.

Infant Muggy Syndrome also belongs to overheating, which often leads to life-threatening conditions for neonates and infants.


How To Check Fever?

How to correctly measure body temperature?

Common body temperature measurement methods include frontal temperature, ear temperature, axillary temperature, oral temperature and rectal temperature. Among them, frontal temperature, ear temperature and axillary temperature are easy to measure, but their accuracy is not as good as that of oral and rectal temperature.

How much is the body temperature to be considered fever?

In medicine, normal body temperature is usually defined as around 36–37 C. Because measuring tools and methods are different, it is too absolute to define fever with a fixed body temperature value.

According to the measurement location and method, the normal range of oral temperature is generally 36.3–37.2℃, and the rectal temperature (anal temperature) is generally 0.3–0.6℃ higher than that of oral temperature, and the axillary temperature is 0.2–0.4℃ lower than that of oral temperature.

But the variation range of the absolute difference of the three is too large, so there is no standard conversion rule.

At present, most medical researches adopt the anal temperature ≥ 38℃ as fever; In clinical work, heating is generally defined as anal temperature ≥ 38℃ or axillary temperature (ear temperature) ≥ 37. 5℃.

Oral method is not commonly used in clinic. Studies have shown that the upper normal oral temperature limit for young adults is 37.2 C in the morning and 37.7 C throughout the day.

Therefore, oral temperature higher than 37.2 C in the morning or 37.7 C in the afternoon could be considered as fever.

Under what circumstances should you go to the hospital for fever?

Adult fever with one or more of the following conditions should be reported to the hospital as soon as possible:

  • Fever during an epidemic, such as a community or local case of COVID-19.
  • Pregnancy.
  • Recent travel history in Africa, Asia, Latin America or the Middle East.
  • Recent hospitalization, surgery, or other invasive medical procedures.
  • Frequent and recurrent infections.
  • Chemotherapy is in progress (if the body temperature exceeds 38 C and lasts for more than 1 hour or the maximum body temperature exceeds 38.3 C).
  • Taking immunosuppressive drugs (eg hormones, drugs to avoid rejection after an organ transplant)
  • If the fever lasts for several days or lasts for 12 to 24 hours, the drug will not be used (if the fever lasts for more than 5 days, an infection which is less common should be suspected).
  • Recently bitten by ticks (ticks, also known as ticks, grass, plants, animals are visible, especially like parasitic on the skin wrinkles).
  • Combined with severe underlying conditions such as diabetes, heart disease, neoplasms, lupus or sickle cell anemia.

Adults with fever accompanied by one or more of the following symptoms should go to the hospital as soon as possible:

  • Rash.
  • Dyspnea.
  • Severe headache or neck/back neck pain.
  • Epilepsy or coma.
  • Severe vomiting or diarrhea.
  • Severe abdominal, back or flank pain.

Infants and young children who have one or more of the following conditions should go to the hospital as soon as possible:

  • For infants under three months of age, it is recommended to visit a doctor promptly in the presence of fever, even if the child appears to be normal in all mental and other respects. Also, do not give your own antipyretic to babies under 3 months of age.
  • Infants aged 3–36 months have fever without other symptoms, with the body temperature exceeding 39 C, or the body temperature exceeding 38.5 C and lasting for more than 24 hours.
  • For children over 3 years of age, fever without other symptoms lasts for more than 3 days, or the body temperature exceeds 38.5 C and lasts for more than 24 hours.
  • The child was also monitored for general condition (signs of serious illness such as drowsiness, neck stiffness, altered mental status, rash, refusals to eat), reactive activity, fluid intake, and urine volume. If there is any abnormal performance, seek medical advice in time.

Children of any age should be admitted to the hospital as soon as possible with one or more of the following conditions:

  • Mouth temperature, rectal temperature, ear temperature or frontal temperature ≥ 40℃.
  • Axillary temperature ≥ 39.4℃.
  • Fever causes convulsions.
  • Repeated high fever, heat back a few hours and fever.
  • Fever with progressive disease such as heart disease, tumours, lupus or sickle cell anemia.
  • Fever with emerging rash.

How To Treat Fever?

What should you do when you have a fever?

Fever is a symptom, and the cause of fever needs to be correctly treated in treatment. The common causes are infectious fever, such as viral infection, bacterial infection, and mycoplasma. There are also other non-infectious causes of fever, such as rheumatic fever, drug fever, and hyperthyroidism.

When fever of unknown cause occurs, it is recommended to see a doctor or consult a doctor in time, and the decision shall be made after the cause is evaluated.

Antipyresis is symptomatic treatment.

In case of fever, rest and drinking water shall be guaranteed first. If it is a small baby, breast milk is preferred to those who have breast milk. If formula fed, formula can be given directly. Older children can give warm water, fruit juice, milk, rice soup, noodle soup these foods can be, mainly liquid, can increase water intake can be. Give sweet or salty can, as long as the baby can drink it. Teenagers and adults can supplement plain boiled water, rehydration salt or suitable drinkable liquid.

Antipyretic. It has previously been recommended that antipyretics be administered when the axillary temperature exceeds 38.5 C. It is because the antipyretic does not shorten the course of the disease and has no obvious effect in preventing and treating "febrile diseases". Therefore, at present, it is considered that if you feel no special discomfort, you can not use the antipyretic even if your body temperature exceeds 39℃. If you feel uncomfortable, you can use the antipyretic even if your body temperature has not reached 38.5 C.

For adolescents and adults, mild fever can lead to general malaise, and if there is no drug allergy or contraindications for the use of antipyretics, such as ibuprofen, oral antipyretics may be administered as needed.

Children can tolerate higher temperatures, often 39 to 40 C without significant discomfort. Therefore, if usually healthy children fever 40℃ or higher, or accompanied by fever because of feeling or performance is not timely, it is recommended to use antipyretic. Medication may be given without arousal if the child is asleep and her temperature is below 40 C.

Children over 6 months of age developed fever, and the safe antipyretics were acetaminophen (10 to 15 mg/kg each time, up to a single dose of 800 mg) and ibuprofen (5 to 10 mg/kg each time, up to a single dose of 600 mg). Administration according to body weight rather than age may be started from the middle to upper limit and adjusted according to the antipyretic effect. It can be repeated up to 4 times within 24 hours and taken again after an interval of 4–6 hours.

Acetaminophen can be used to reduce fever for children aged 3–6 months, with the same usage and dosage as above. Consultation with a doctor or doctor is also recommended.

The baby under 3 months old is febrile. Don't take the medicine by yourself. Go to the hospital first.

Can children use antipyretic drugs alternately?

Alternating use of the two antipyretics is not recommended.

However, the purpose of medication is to improve the comfort of children with fever. If the body temperature is still high after 3–4 hours of taking acetaminophen or ibuprofen, and the discomfort still does not improve, acetaminophen can be replaced with ibuprofen, and vice versa.

Does rubbing the body with alcohol help reduce fever?

For small babies, do not use alcohol to wipe, ice and other methods of cooling. After easy alcohol volatilization, it will be absorbed through alveolar membrane and possibly through skin, leading to central nervous system poisoning and affecting intellectual development.

Ice application is also easy to cause discomfort to infants and young children, and improper use will cause local skin frostbite.

Don't wear too many clothes or a thick quilt, just wear it as usual.

If you feel cold, you can wrap your hands and feet properly and add some clothes. If you feel hot, you can reduce your clothes. Clothing to wear comfort-based, but do not take the quilt to cover your body to avoid aggravating the high temperature.

If it is an infant, it is very easy to cause overheating syndrome with thick clothes, and there will be life-threatening.

Can fever caused by heatstroke be used with antipyretics?

Don't take any antipyretic if it's heatstroke. When suffering from heatstroke, you should leave the sultry environment, take off your clothes, wipe yourself with warm water, drink a small amount of water in several times, and go to the hospital in time.

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