A healthy body functions best at an internal temperature of about 37°C (98.6°F). But everyone has their own individual "normal" body temperature, which may be slightly higher or lower. Our bodies also constantly adapt their temperature to environmental conditions. It goes up when we exercise, for instance. And it is lower at night, and higher in the afternoon than in the morning.
Our internal body temperature is regulated by a part of our brain called the hypothalamus. The hypothalamus checks our current temperature and compares it with the normal temperature of about 37°C. If our temperature is too low, the hypothalamus makes sure that the body generates and maintains heat. If, on the other hand, our current body temperature is too high, heat is given off or sweat is produced to cool the skin.
Strictly speaking, body temperature refers to the temperature in the hypothalamus and in the vital internal organs. Because we cannot measure the temperature inside these organs, temperature is taken on parts of the body that are more accessible. But these measurements are always slightly inaccurate.
What causes a fever?
People get a fever when their brain sets the body temperature higher than normal. This may happen as a reaction to germs such as viruses or bacteria, but it can also happen as a reaction to substances that are made by the body, such as prostaglandins. Our body produces prostaglandins to fight off germs.
A body temperature of 38°C (100.4°F) or more is considered to be a fever. Temperatures above 39.5°C (103.1°F) are considered to be a high fever, and very high fever is defined as any temperature above 41°C (105.8°F). A temperature between 37.5°C and 38°C is an elevated body temperature.
The regulation of body temperature doesn't always work perfectly in younger children. Compared to older children and adults, they also sweat less when it is warm, and it takes longer for them to start sweating. That is why they are more likely to react with a fever. Babies and young children have a higher body temperature than older children. This is because their body surface area is larger in relation to their body weight. Their metabolism is more active too. Newborns usually have an average body temperature of 37.5°C.
Sources
Andreae. Lexikon der Krankheiten und Untersuchungen. Stuttgart: Thieme; 2008.
Hoffbauer G, Schaenzler N. Handbuch Medikamente für Kinder – Medikamente und Wirkstoffe, Risiken und Nebenwirkungen, alternative Behandlungsmöglichkeiten.Reinbek: Rowohlt; 2005.
Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J. Harrison’s Principles of internal medicine. New York: McGraw-Hill Companies. 18th ed; 2011.
National Collaborating Centre for Women's and Children's Health, National Institute for Health and Care Excellence (NICE). Feverish illness in children: assessment and initial management in children younger than 5 years. May 2013. (NICE Clinical Guideline; CG160).
Pschyrembel W. Klinisches Wörterbuch. Berlin: De Gruyter; 2014.
Ward MA. Fever in infants and children: Pathophysiology and management. In:UpToDate. March 24, 2016.
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FAQs
If your body temperature rises to 99.6 degrees or higher, you have a fever. How does this rise in temperature occur? The hypothalamus responds to different factors, such as infectious organisms and injury, by releasing fever-producing chemicals that change body temperature.
What is the body temperature for a fever? ›
The average temperature has traditionally been defined as 98.6 F (37 C). A temperature taken using a mouth thermometer (oral temperature) that's 100 F (37.8 C) or higher is generally considered to be a fever. Depending on what's causing a fever, other fever signs and symptoms may include: Sweating.
Which system regulates body temperature? ›
The regulation of body temperature is one of the most critical functions of the nervous system.
How is body temperature regulated in homeostasis? ›
Even at resting state, the muscles, liver, brain, heart, kidneys, and other organs generate constant heat. Body temperature is maintained at homeostasis by dissipating this generated excess heat outside the body. Moreover, we must respond to temperature changes caused by the environment.
How do you regulate temperature with a fever? ›
Take paracetamol or ibuprofen in appropriate doses to help bring your temperature down. Drink plenty of fluids, particularly water. Avoid alcohol, tea and coffee as these drinks can cause slight dehydration. Sponge exposed skin with tepid water.
Why is body temperature regulated? ›
Mammals use thermoregulation to keep the body within a tight temperature range. This is essential for health, as it allows organs and bodily processes to work effectively. If a person's body temperature strays too far from 98.6°F (37°C), they can develop hyperthermia or hypothermia.
What is the fastest way to cure a fever? ›
Rest and drink plenty of fluids. Medication isn't needed. Call the doctor if the fever is accompanied by a severe headache, stiff neck, shortness of breath, or other unusual signs or symptoms. If you're uncomfortable, take acetaminophen (Tylenol, others), ibuprofen (Advil, Motrin IB, others) or aspirin.
Is a temp of 99 a fever? ›
Fevers defined
Normal body temperatures sit between 97 F to 99 F. A fever is a temperature of 100.4F or higher. There are low-grade fevers and more serious fevers, depending on the sick person's age. A serious fever is warmer than 103 F in young adults.
Why does a fever go up at night? ›
Cortisol is closely linked to your immune system function. Cortisol is higher during the day, and these higher levels suppress your immune activity to a large degree. When cortisol levels go down at night, your immune system is more active in fighting illness or infection. This is why fevers spike at night.
What temperature is too low for a person? ›
If your temperature is near or dipping below 95 degrees, it's too low and it indicates hypothermia. People with hypothermia can lose consciousness or go into shock. If you or someone else has signs of hypothermia, seek emergency medical care immediately. Call 911 or go to the ER at once.
Poikilothermia refers to the inability to regulate core body temperature. Clinically, poikilothermia can be manifested by hypothermia (core temperature less than 35°C/95°F) or hyperthermia (core temperature > 37.8°C /100°F).
Which substance induces fever? ›
A pyrogen is a substance (infectious organisms or their product toxins or cytokines) that provokes fever. Exogenous pyrogens are substances, which originate outside the body and which are capable of inducing interleukins.
What causes fever in adult? ›
Almost any infection can cause a fever, including: Bone infections (osteomyelitis), appendicitis, skin infections or cellulitis, and meningitis. Respiratory infections such as colds or flu-like illnesses, sore throats, ear infections, sinus infections, mononucleosis, bronchitis, pneumonia, and tuberculosis.
Why can't I regulate my body temperature at night? ›
At night, during REM sleep, your brain (your hypothalamus) stops regulating body temperature. During this time when your body's innate ability to thermoregulate, or maintain your body temperature, is affected, the need for ideal external temperatures increases.
Why does body temperature increase without fever? ›
What's the reason for being hot but not having a fever? No fever but hot body is said to have many causes, the most common of which is related to hormones in menopause. Another cause of this abnormality is: Abnormal changes in the hypothalamus of the brain (the main thermoregulatory center of the human body).
How do you explain body temperature? ›
Body temperature is a measure of how well your body can make and get rid of heat. The body is very good at keeping its temperature within a safe range, even when temperatures outside the body change a lot. When you are too hot, the blood vessels in your skin widen to carry the excess heat to your skin's surface.
