Human body temperature facts for kids

Normal human body-temperature, also called normothermia or euthermia, is the usual temperature range found in humans. This range is typically between 36.5–37.5 °C (97.7–99.5 °F).

Your body temperature can change based on many things. These include your sex, age, time of day, how active you are, and if you are sick or a girl having her period. Where you measure the temperature on your body also makes a difference. Your body works hard to keep its temperature in a normal range. This process is called thermoregulation, and your brain controls it.

How We Measure Body Temperature

A medical thermometer showing a temperature reading of 38.7 °C (101.7 °F)

Checking a person's temperature is a first step in a health check-up. There are different types of medical thermometers and places to measure temperature:

• Inside the bottom (rectal temperature)
• In the mouth (oral temperature)
• Under the arm (axillary temperature)
• In the ear (tympanic temperature)
• On the forehead, over a specific artery
• Using special heat sensors

Why Your Temperature Changes

Daily changes in body temperature, from about 37.5 °C (99.5 °F) (10 a.m. to 6 p.m.) to about 36.4 °C (97.5 °F) (2 a.m. to 6 a.m.).

Your body has a special system called thermoregulation that acts like a thermostat. It keeps your body at the best temperature for all its chemical reactions. For a long time, the average human body temperature was thought to be 37 °C (98.6 °F). This idea came from studies in the 1800s.

However, newer studies show that the average temperature for men and women is closer to 36.4 °C (97.5 °F). No one has the exact same temperature all day long. Your temperature naturally goes up and down throughout the day. This is controlled by your body's internal clock, called your circadian rhythm. Your temperature is usually lowest about two hours before you normally wake up. Also, your temperature changes based on what you are doing and the temperature around you.

Your normal body temperature can also vary a little from one day to the next. It might change by as much as 0.5 °C (0.9 °F). So, your highest or lowest temperature on one day might not be exactly the same on the next day.

The normal range for oral temperature (taken in the mouth) is about 36.8 ± 0.5 °C (98.2 ± 0.9 °F). This means an oral temperature between 36.3 and 37.3 °C (97.3 and 99.1 °F) is likely normal.

Different ways of measuring temperature give slightly different results. For example, internal measurements (like rectal) are usually a bit higher than oral measurements. Oral measurements are a bit higher than skin measurements. Even though there are averages, a wide range of temperatures is normal for healthy people.

Your body temperature changes by about 0.5 °C (0.9 °F) during the day. It's lower in the morning and higher in the late afternoon or evening. This happens as your body's needs and activities change. Your temperature is lowest during the second half of your sleep cycle. This lowest point is an important sign of your circadian rhythm. Your temperature also changes if you are hungry, sleepy, sick, or cold.

Daily and Monthly Rhythms

Body temperature naturally changes throughout the day. It's usually lowest around 4 a.m. and highest in the late afternoon, between 4:00 and 6:00 p.m. (if you sleep at night). So, an oral temperature of 37.3 °C (99.1 °F) might be normal in the afternoon but not in the early morning.

For girls, body temperature also changes with their menstrual cycle. This is called a circamensal rhythm. A girl's basal body temperature (her lowest temperature during rest) goes up after ovulation. This happens because a hormone called progesterone increases. Some people use this temperature change to track ovulation for fertility awareness.

Other Factors Affecting Temperature

Your temperature can also change with the seasons of the year. This is called a circannual rhythm. Studies have shown different patterns for people living in different climates.

People who are very active often have bigger changes in their body temperature during the day. They might have lower temperatures in the early morning and similar or higher temperatures later in the day compared to less active people.

As people get older, their average body temperature and how much it changes daily tend to decrease. For older adults, even a slightly high temperature can be a sign of a serious problem. One study even suggested that the average body temperature has gone down since the 1850s. This might be because there are fewer infections and better hygiene now.

How Measurement Methods Differ

Different ways of taking your temperature give different results. The reading depends on where on the body the temperature is measured.

Oral temperatures can be affected by what you drink, eat, or if you smoke or breathe with your mouth open. Cold drinks or food can lower oral temperatures. Hot drinks, hot food, chewing, and smoking can raise them.

Each measurement method also has different normal ranges, and these can vary slightly between boys and girls.

Infrared Thermometers

Infrared thermometer Infrared thermometers, like those used in the ear or on the forehead, use infrared sensors to measure heat. In 2016, studies found that these thermometers can be accurate, but their accuracy can vary. This includes ear thermometers used for children.

How Sleep Affects Temperature

Sleep also affects your temperature. Normally, your body temperature drops a lot when you go to bed and stays low through the night. If you don't get enough sleep for a short time, your temperature at night might be higher than usual. But if you don't get enough sleep for a long time, your temperature might actually go down. Trouble sleeping or poor sleep quality can lead to smaller and later drops in body temperature. Also, waking up too early, sleeping in, jet lag, or changes in shift work can affect your body temperature.

Understanding Body Temperature Changes

Fever

Fever Your body has a "setpoint" for its temperature, which is the temperature it tries to maintain. When this setpoint is raised, you get a fever. Most fevers are caused by infections. You can often lower a fever with special medicines called antipyretics.

A temperature higher than 37.2 °C (99.0 °F) in the early morning, or higher than 37.7 °C (99.9 °F) in the late afternoon, is usually considered a fever. This is true if the temperature rise is because your brain's setpoint has changed. For older people, a slightly lower temperature might still be considered a fever. Your normal daily temperature usually changes by about 0.5 °C (0.90 °F), but it can change more if you are getting over a fever.

If your body is at its best temperature, it's called afebrile, meaning "without fever". If your temperature is high, but your body's setpoint hasn't changed, it's called hyperthermia.

Hyperthermia (Too Hot)

Hyperthermia Hyperthermia happens when your body makes or takes in more heat than it can get rid of. This often happens from being in very hot places for too long. Your body's heat control system gets overwhelmed and can't cool you down. This causes your body temperature to rise too much.

Hyperthermia at or above 40 °C (104 °F) is a serious medical emergency. It needs immediate treatment. Common signs include headache, confusion, and feeling very tired. If you are also dehydrated from sweating, your skin might be dry and red.

Mild hyperthermia is often called heat exhaustion. More severe hyperthermia is called heat stroke. Heatstroke can happen suddenly, but it usually follows milder stages that weren't treated. To treat it, you need to cool down and rehydrate your body. Fever-reducing medicines don't work for this. You can move to a cooler, shaded place, drink water, take off extra clothes, or sit in front of a fan. Taking a bath in cool water or just washing your face can also help.

With a fever, your brain raises your body's core temperature. With hyperthermia, your body temperature goes up without your brain's heat control centers changing their setpoint.

Hypothermia (Too Cold)

Hypothermia In hypothermia, your body temperature drops below what it needs for normal body functions. This usually happens from being in very cold air or water. Sometimes, doctors will purposely lower a person's body temperature as a medical treatment. Signs usually appear when your body's core temperature drops by 1–2 °C (1.8–3.6 °F) below normal.

Basal Body Temperature

Basal body temperature Basal body temperature is the lowest temperature your body reaches while resting, usually during sleep. It's often measured right after you wake up, before you do any physical activity. For girls, this temperature changes at different points in their menstrual cycle. This can be used to track ovulation to help with or avoid pregnancy. This is part of fertility awareness.

Core Body Temperature

Core temperature is the temperature deep inside your body, like in your liver. It's different from the temperature of your skin or limbs. Your body keeps its core temperature in a very small range so that important chemical reactions can happen. If your core temperature gets too high (hyperthermia) or too low (hypothermia) for too long, it can be very dangerous.

Measuring temperature inside the heart with a special tube (catheter) is considered the most accurate way to find core temperature. However, this is very invasive. A common way to estimate core body temperature is by taking a rectal temperature. Rectal temperature is usually about 1 Fahrenheit (or 0.55 Celsius) degree higher than an oral temperature taken at the same time. Ear thermometers try to measure core body temperature too, because the ear drum shares blood supply with the brain. But this method is not as accurate as rectal measurement, especially for finding fevers in children.

Until recently, measuring core body temperature directly meant swallowing a device or having a probe surgically inserted. So, doctors often used other methods. Rectal temperature is generally seen as the most accurate way to check core body temperature, especially if someone is very cold. Newer methods using heat flux sensors have also been developed and show similar accuracy to more invasive methods.

Temperature Ranges

Here's a look at what different body temperatures mean:

Hot Temperatures

• 44 °C (111.2 °F) or more – This temperature is almost always deadly. However, some people have survived temperatures up to 46.5 °C (115.7 °F).
• 43 °C (109.4 °F) – Usually leads to death or serious brain damage. You might have constant fits and go into shock. Your heart and breathing could stop.
• 42 °C (107.6 °F) – You might look pale or very red. You could become unconscious, have severe confusion, vomit, and have fits.
• 41 °C (105.8 °F) – (Medical emergency) – You might faint, vomit, have a bad headache, feel dizzy, confused, see things that aren't there, or feel very sleepy. Your heart might beat fast, and you could feel breathless.
• 40 °C (104 °F) – You might faint, become dehydrated, feel weak, vomit, have a headache, feel breathless, and sweat a lot.
• 39 °C (102.2 °F) – You will sweat a lot, look red and flushed. Your heart rate will be fast, and you'll feel breathless. You might feel very tired. Children and people with epilepsy might have fits at this temperature.
• 38 °C (100.4 °F) – (This is called hyperthermia if it's not caused by a fever) – You'll feel hot, sweaty, thirsty, very uncomfortable, and slightly hungry. If it's a fever, you might also have chills.

Normal Temperature

• 36.5–37.5 °C (97.7–99.5 °F) is the typical range for normal body temperature.

Cold Temperatures

• 36 °C (96.8 °F) – You'll feel cold and shiver a little to moderately. Your body temperature might drop this low during sleep, which can be normal.
• 35 °C (95 °F) – (Hypothermia is less than 35 °C (95 °F)) – You'll shiver a lot, feel numb, and your skin might look bluish or gray. There's a chance of heart problems.
• 34 °C (93.2 °F) – You'll shiver severely, lose feeling in your fingers, look blue, and be confused. Your behavior might change.
• 33 °C (91.4 °F) – You'll be moderately to severely confused, sleepy, have slow reflexes, and stop shivering. Your heartbeat will be slow, and breathing shallow. You might not respond to some things.
• 32 °C (89.6 °F) – (Medical emergency) – You might see things that aren't there, be very confused, and become extremely sleepy, possibly falling into a coma. You won't shiver (you might even think you're hot). Your reflexes might be gone or very weak.
• 31 °C (87.8 °F) – You'll be in a coma and very rarely conscious. Your reflexes will be gone or very slight. Your breathing will be very shallow, and heart rate slow. There's a chance of serious heart rhythm problems.
• 28 °C (82.4 °F) – Severe heart rhythm problems are likely, and breathing might stop at any time. The person might appear to be dead.
• 24–26 °C (75.2–78.8 °F) or less – Death usually happens because of an irregular heartbeat or breathing stopping. However, some patients have survived with body temperatures as low as 13.7 °C (56.7 °F).

Sometimes, you can tell if someone is too cold without them saying anything. For example, if they are very still and slow in their movements, sneezing, or if their skin looks unusually pale (for light-skinned people).

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See also

In Spanish: Temperatura del cuerpo humano para niños