Fever is one of the main signs of infection with coronavirus – if we catch an infection, our temperature may rise as part of our immune response to kill it.
The increase is caused by chemical messengers released by immune cells that travel to the hypothalamus, the part of the brain that controls temperature and tells it that it increases the heat in your body – also called the core temperature.
For most of our lives, our body temperature hovers around 37c (between 36.5c and 37.5c). It is classified as a fever if it exceeds 37.8c.
“Viruses die earlier if temperatures rise above 38C,” said Dr. William Bird, a family physician in Reading, Berks.
Not only does a high temperature kill the virus directly, it also triggers a cascade of reactions in the body that trigger immunity. For example, a temperature above 37c can accelerate the activity of NF-kB proteins in our cells, turning on genes involved in the immune response, a 2018 study from the University of Warwick found.
Fever is one of the main signs of infection with coronavirus – if we catch an infection, our temperature may rise as part of our immune response to kill it
Other research has shown that specific virus-killing cells, T cells, also increase their activity when temperatures rise.
“There is a belief that lowering the temperature can lead to recovery and prolong the disease,” says Dr. Bird. Saying that a fever can be serious, however, so seek advice from a primary care physician, especially in babies and young children.
Here, experts reveal what everyone needs to know about this essential measurement – and the surprising factors that can affect it.
WORK OUT WHAT ‘NORMAL’ IS FOR YOU
Our body temperature naturally fluctuates during the day and at night.
A study based on measurements from more than 300 people found that it is lowest between 3am and 5am and highest between 4pm and 6pm, with a difference of about half a degree Celsius between the two, according to U.S. researchers writing in the Journal of General Internal Medicine in 2018. This suggests that if you want to take a base temperature, the first morning is the best time to measure.
However, doctors have noticed that the temperature can go on and off all day in people with coronavirus, says Dr. Patricia Macnair, an aging and palliative care specialist in Surrey, although it is not yet known why this is so.
“If you’re concerned, take more than one temperature reading a day – say, morning, noon, and evening,” she says.
“If you think you’re infected, look out for other symptoms [for example, a dry cough, loss of smell or taste and fatigue] and if they get more serious, call 111. “
Contrary to popular belief, you don’t necessarily feel warm when you have a fever. “This is one of the big misconceptions about high temperatures,” says Dr. Bird
WE GET COLLER AS WE AGE
Younger women of normal body weight generally have higher body temperatures than older overweight men, according to a 2011 study in the Journals of Gerontology, which analyzed the body temperature of more than 18,600 people.
The analysis also found that men were generally colder than women, with scientists suggesting that female hormones may play a role (as temperatures often drop after menopause and are known to fluctuate during the menstrual cycle).
SHOULD YOU SHARE AT HOME?
It is thought that coronavirus can live on hard surfaces like plastic for up to 72 hours, if not longer, so at this point you shouldn’t be sharing thermometers – even between family members.
But if you only have one, you can wash the end of an oral thermometer with soap and water, says London GP. Ross Perry, or wipe it off with an alcohol or antimicrobial wipe if you have one.
With an ear thermometer, the best solution is to use disposable tips.
It also found that women in their twenties had an average body temperature of 36.5 c, while women in their eighties had an average body temperature of 36.1 c. A similar decrease was found in men. “We don’t know why it happens, but the body generally slows down as we age and this can be reflected in temperature,” says Dr. Macnair.
Fat can make you warmer
And the more someone weighed, the higher the average temperature was. It is unclear exactly why this should be so, but one theory is that fat-released inflammatory chemicals may be the cause of the elevated temperature.
THE ELDERLY CAN BUG BUT NO Fever
Another fascinating theory is that a lower body temperature can be associated with longer life. Lowering body temperature in mice has been shown to extend lifespan by about 20 percent.
In addition to this lower baseline temperature in older people, their immune systems don’t cause such intense responses to infections. As such, older people may not always develop a fever in response to infection.
“This means that you should not rely on the presence of high temperature as the only sign of infection, and people should pay extra attention to other symptoms such as pain, cough, or shortness of breath – and unusual levels of confusion,” Dr. Macnair.
EAR THERMOMETERS ARE BEST FOR THE HOME
The most accurate measurement of body temperature, often used in intensive care units, comes from the use of a rectal thermometer because it measures in the body rather than the rim.
But because you are unlikely to want to use this approach at home, the next best option in the ear is to take the temperature of the eardrum (the eardrum), Dr. Bird.
The eardrum shares the same blood supply as the hypothalamus, so it gives a good idea of what is happening internally.
Ear thermometers use an infrared light to measure energy coming from the eardrum (shown, Braun ThermoScan 7 ear thermometer, £ 49.99, argos.co.uk)
Ear thermometers use an infrared light to measure energy coming from the eardrum (shown, Braun ThermoScan 7 ear thermometer, £ 49.99, argos.co.uk).
But don’t test the temperature in the ear if you’ve been on it, as it can lead to higher readings when the ear is warm, a study in Turkey found.
Instead, use the other ear – then stick to that ear when measuring during the day to get the most accurate assessment of changes in body temperature.
Ear thermometers should also not be used if you have an ear infection, as the ear is already warm from inflammation.
If you need to use an oral thermometer, don’t use it within 20 to 30 minutes after a hot or cold drink, eating, exercising, or smoking, says Dr. Ross Perry, a family physician in London. This is because all of them can temporarily raise the temperature in the mouth and, in the case of exercise, throughout the body.
“Leave the thermometer under the tongue for one or two minutes and try to hold still for the most accurate reading,” he says.
Despite the convenience, forehead strips or taking temperature in the armpit is believed to be least accurate because they are really external. “If you need to take a temperature under the arm, add 1c to the figure to get a more accurate reading,” says Dr. Bird.
YOUR SPIRIT CAN GIVE A FEVER
Stress can cause a rise in body temperature – a condition called psychogenic fever.
It is most common in children and adolescents, with an analysis by researchers in Japan in 2007 that stress or psychological and emotional arousal accounted for 18 percent of unexplained cases of fever in children.
IF YOU FEEL HOT, IT MAY BE COLD
Contrary to popular belief, you don’t necessarily feel warm when you have a fever.
“This is one of the big misconceptions about high temperatures,” says Dr. Bird.
“When you’re hot, you almost certainly don’t have a fever, probably a cold.
“When we have a fever, we usually feel cold and wary and want to pack up,” he explains.
“You do feel warm, so feeling the forehead with the back of one hand is actually a really good way to see if you have a fever if you don’t have a thermometer.
“If your skin feels cold, you almost certainly don’t have one.”