We have published revised versions of the OMRON Privacy Policy and Cookie Policy. Your use of our products and services is subject to these revised terms.

This website uses cookies. By continuing to browse through this website, you agree to our Cookie Policy which has been revised in May 2018.

Allow cookies


Body temperature elevated above the normal range

Body Temperature and Fever

Body temperature is a basic condition for the proper operation of the cells. It is configured by many internal organs with the control of the nervous system on the delicate balance of heat production and heat loss. This mechanism (called thermoregulation) ensures the stable operation of vital functions by keeping the body at optimum operating internal temperature.

Normal body temperature is in average 36.5–37.5 °C (97.7–99.5 °F), although it varies somewhat among individuals (gender, age). Additionally, temperature can vary according to physical activities, throughout the day, and due to external factors, e.g. with the change of seasons.

It’s also very much dependent on at which part of the body the measurement is taken. The most accurate optimal values derive from rectal measurement: 37.0-37.5 °C (98.6-99.5 °F), while oral measurement produces slightly lower results: 36.8° ± 0.4 °C (98.2° ± 0.7 °F). Measurements taken on the skin (armpit, ear, forehead) gives the lowest values out of these types: 36.5 °C (97.7 °F), since these correlate relatively poorly with the core body temperature.  

About Fever

Fever (body temperature elevated above the normal range) is a common symptom of diseases. It plays a crucial role in how the body fights against infections by disrupting the reproduction of germs and viruses and increasing the activity of the immune system. 

Fever is one of the most common medical signs. It is part of about 30% of healthcare visits by children and occurs in up to 75% of adults who are seriously sick. Being an important defense mechanism, treatment for fever is not necessary but it may increase the comfort of the patient and help them rest.

However, the too high body temperature (permanently above 40 °C / 104 °F) impairs the organism. If the internal temperature stays above 41 °C (106.8 °F) for a longer while, it leads to enduring brain damage. Body temperature above 43 °C (109.4 °F) is almost certainly lethal.


Fever appears when the body temperature rises above its normal range. It can be caused by a number of reasons: in most cases by infectious diseases (such as flue, angina and pneumonia), less frequently by hormone imbalance, metabolic disorders, certain inflammatory conditions (such as rheumatoid arthritis), a malignant tumor or even extreme sunburn or certain medications and immunizations (vaccines). Sometimes the cause of a fever can't be identified. If you have a temperature of 101 F (38.3 C) or higher for more than three weeks and your doctor isn't able to find the cause after extensive evaluation, the diagnosis may be fever of unknown origin.

The symptoms can be the following:

  • Sweating
  • Shivering
  • Headache
  • Muscle aches
  • Loss of appetite
  • Dehydration
  • General weakness

High fevers between 39.4 °C (103 °F) and 41.1°C (106 °F) may cause:

  • Hallucination
  • Irritability
  • Convulsions
  • Bafflement
  • Delirium
  • Black-out
  • Spasm seizure, vomiting, diarrhea (in children of very young age)


As fever is not by itself an illness but a defense mechanism, slightly elevated body temperature does not need any treatment.

However, if it rises above 39.4 °C (103 °F), some actions have to be taken to reduce it, since it means that the body is no longer able to control its inner temperature.

This can either be done by using antipyretics (medications against fever), or by taking a cooling bath. The way of treatment should be defined by a physicist, based on the underlying cause, the age and condition of the patient. Infectious diseases require anti-pathogenic drugs.

By all means extra attention should be paid to increased water-intake, to compensate for dehydration.  

Young children with even low fever require special attention and immediate treatment aiming to reduce the body temperature (cooling bath or cold pack first, before turning to medications). 

If an infant younger than 4 months old has rectal temperature above 38 °C (100.4 °F), immediately call your doctor or go to an emergency room, because it could be a sign of a potentially life-threatening infection.

The same action must be taken if any child has a fever above 40 °C (104 °F).


The risk of getting infectious diseases can be mitigated by paying attention to the following tips:

  • Wash hands thoroughly and frequently especially before eating, after using the toilet, after spending time in a crowd/on public transportation or around someone who's sick
  • Dress up warm enough when going outside (cold air makes the veins contract and the blood supply worsen, hence the organism becomes less resistant to infections)
  • Cover your mouth when you cough and your nose when you sneeze
  • Avoid sharing cups, water bottles and utensils with your child