11 Fascinating Facts About Body Temperature

The average normal body temperature is generally considered to be 98.6 degrees F, according to the U.S. National Library of Medicine. But "normal" body temperature can range from 97 degrees F to 99 degrees F, and what’s normal for you may be a little higher or lower than the average body temperature.

Your body is always adapting its temperature in response to environmental conditions. For example, your body temperature increases when you exercise. And if you check your temperature with a thermometer, you will see that it’s higher in the late afternoon and evening than first thing in the morning when you rise, according to the Mayo Clinic.

Babies and young children have a higher body temperature than older kids and adults, because the surface area of their bodies is larger relative to their weight, and their metabolism is more active. Newborns typically have an average body temperature of 99.5 degrees F.

A fever is a temporary increase in your body temperature, and it’s often caused by illness, according to the Mayo Clinic. A rectal, ear, or temporal artery (forehead) temperature of 100.4 degrees or higher generally indicates a fever. Fevers usually subside within a few days. If you have a fever, you may also experience the following symptoms:

• Chills and shivering
• Sweating
• Headache
• Muscle aches
• Loss of appetite
• Irritability
• Dehydration
• General weakness

For adults, a body temperature of 103 degrees F or higher can be a cause for concern, and warrants a call to your doctor, according to the Mayo Clinic. Also call your doctor if along with a fever, you have a severe headache; an unusual skin rash; unusual sensitivity to bright light; stiff neck and pain when you bend your head forward; mental confusion; persistent vomiting; difficulty breathing or chest pain; abdominal pain or pain when urinating; or convulsions or seizures.

For infants and toddlers, a temperature that is only slightly higher than usual could be a sign of a serious infection, according to the Mayo Clinic. Call your doctor if your child is younger than 3 months and has a rectal temperature of 100.4 degrees F or higher; between 3 and 6 months old and has a rectal temperature up to 102 degrees F and seems atypically irritable, lethargic, or uncomfortable, or has a temperature higher than 102 degrees F; or between 6 and 24 months and has a rectal temperature higher than 102 degrees F that lasts longer than one day.

If your child is 2 years old or older, call your doctor if they have a fever that lasts longer than three days, or if they seem unresponsive to you.

Young children from 6 months to 5 years old might have febrile seizures with a high body temperature, which usually involve loss of consciousness and shaking of limbs on both sides of the body, according to the Mayo Clinic. Call for emergency medical care if a seizure lasts longer than five minutes, or take your child to the doctor as soon as possible after the seizure to figure out what caused it.

Most people fret over a fever, but it actually can be helpful. Various over-the-counter medications can lower a fever, such as acetaminophen (Tylenol) or ibuprofen (Advil, Motrin IB), but sometimes it's better left untreated, according to the Mayo Clinic. This is because fever seems to play an important role in helping your body fight off infections. Still, your doctor may prescribe an antibiotic if he or she suspects a bacterial infection, such as pneumonia or strep throat.

Fever is one of the symptoms of COVID-19, the illness caused by the novel coronavirus SARS-CoV-2, according to the Centers for Disease Control and Prevention (CDC). Low body temperature is not a symptom of COVID-19. 

If you think you may have been exposed to the new coronavirus, the CDC recommends that you take your temperature twice daily to see if you have a fever. The CDC defines a fever as 100.4 degrees F or higher. If you have a child younger than 4 years old, use an ear thermometer to take their temperature, or place a regular thermometer under your child’s arm in the center of their armpit, the CDC recommends. If your child’s armpit temperature is 99.4 degrees F or higher, they have a fever.

If you have a high body temperature or any other symptoms of COVID-19 and want to get tested, the CDC recommends calling your state or local health department or a medical provider. Most people with COVID-19 have mild illness and are able to recover at home, the CDC notes.

RELATED: Coronavirus 101: Your Ultimate Guide to COVID-19

If it seems like you're always cold, even during the dog days of summer, it could be your age. Studies show that as we age, our average body temperature declines slightly. A study published in the Journal of Clinical Nursing that measured the body temperature of 133 nursing home residents found that body temperature was below average in those 65 to 74 years old; even lower in people 75 to 84; and lowest among those older than 85, some of whom had a low body temperature of 93.5 degrees F under normal circumstances. This is important to know, because seniors may actually be running a fever at lower temperatures than younger adults.

There really might be something to the saying “cold hands, warm heart.” In a study published in the Lancet, researchers at the University of Utah in Salt Lake City found that women’s core body temperature is, on average, 0.4 degrees higher than men’s (97.8 vs. 97.4). But women’s hands are 2.8 degrees F colder than men's on average — 87.2 degrees F, compared with 90 degrees F for men.

Remember your mom telling you to wear a hat when it's cold outside, because most body heat is lost through your head? It turns out that her advice may not have been completely spot-on, according to an article published in the medical journal BMJ. Studies have shown that there is nothing unique about your head when it comes to heat loss — any part of your body that is not covered loses heat and will reduce your core body temperature proportionally.

Fibbing won't cause your nose to grow, but it will make it colder. Despite this discrepancy with the old children's story, researchers at the University of Grenada in Spain dubbed their findings the "Pinocchio effect." In a study published in April 2018 in the Journal of Investigative Psychology and Offender Profiling, they used thermal imaging to demonstrate that the anxiety brought on by a lie causes the temperature of the nose to decrease and the areas around the forehead to increase.

Like your food spicy? It may raise your body temperature — and your metabolism. A study published in Physiology and Behavior had participants add about 1 gram of red pepper to their food. Their core body temperature rose, but their skin temperature was lower. Study authors theorize that this increased heat production along with decreased sensations of appetite demonstrates a potential benefit of consuming red pepper for those who are trying to manage their weight, especially for people who don’t usually eat spicy foods.

Therapeutic hypothermia is a type of treatment sometimes used for people who have cardiac arrest (when the heart suddenly stops beating), according to Johns Hopkins Medicine. Once the heart starts beating again, healthcare providers use cooling devices to lower the patient’s body temperature to around 89 to 93 degrees F. Lowering the body temperature right after cardiac arrest can reduce damage to the brain, and raises the chances that the person will recover.

This isn't just crime-show fodder. After people die, they no longer produce body heat, and the body slowly cools. This process is called algor mortis (Latin for “the coldness of death”). Algor mortis has been used as a tool in forensic investigations to estimate how long a person has been deceased after their body has been discovered. But various factors affect body temperature, so it’s not a totally reliable or accurate technique.