When Does A Fever Become Dangerous?


6 Min Read

A fever above 41°C (105.8°F) can cause multiple organ failure and warrants immediate medical attention. Regardless of intensity, a fever accompanied by other symptoms like headaches, rashes, low BP, etc. can be indicative of serious underlying conditions and must be investigated further. People suffering from dementia or heart or lung diseases must not ignore a fever.

You’re running a temperature and feel exhausted. Or worse still, your child’s all hot and flushed. Time to hit the panic button? A fever may leave you feeling run down and depleted, but a trip to the emergency room isn’t warranted every time.

A fever tipping into delirium or causing brain damage – that’s a fear many a parent has felt over and again! In fact, you’ll find research aplenty on the subject, with studies showing that most parents fall victim to “fever phobia,” where you worry fevers, even low-grade or moderate ones, can cause serious neurological side effects.

The reality is that fever is not an illness. On the contrary, it is a part of your body’s natural defense against infection and, in most cases, is fighting for than against you! A slight fever can make it harder for most bacteria and viruses that cause infections to survive. Fever also activates your body’s immune system, putting it on red alert, all ready to defend you. Ancient sciences like Ayurveda also consider fever to be a protective mechanism aimed at flushing out toxins, improving immune function, and holding back nutrients from bacteria.1

So what exactly is a fever? When your body temperature rises above its normal level you have a fever. The range of “normal temperature” varies from person to person depending on factors like your age, sex, and even the time of the day. However, if you’re a healthy adult and your early morning temperature is higher than 37.2°C (99.0°F) or late afternoon temperature is higher than 37.7°C (99.9°F) you probably have a fever.2 A low-grade fever is one with a temperature of 38.9°C (102.0°F) or less, while a moderate fever shows a temperature of 40°C (104.0°F) or less.

A body temperature over 41.5°C (106.7°F) is defined as hyperthermia and should be treated as a medical emergency.3

What Causes Fever?

Most fevers are caused by common infections like ear infections, flu, roseola, tonsillitis, upper respiratory tract infections, kidney or urinary tract infections, chickenpox, and whooping cough. Some serious bacterial illnesses that are associated with fever include meningitis, septicemia, and pneumonia. Fever can also be caused by certain medicines, heat exhaustion, cancers, and autoimmune diseases.4

What Happens When You Get A Fever?

Mild or moderate fevers – up to 40.55°C (105°F) – may cause weakness but are not in themselves a significant threat to health. Most of us can tolerate these fevers without any serious trouble. And although the fever may be uncomfortable, it doesn’t necessarily need treatment. About 2–3 percent of children get seizures triggered by fever, but they are generally very brief episodes and are not known to cause any permanent harm.5 A fever will generally not cause brain damage unless it goes over 42°C (107.6°F).

But, if the fever is accompanied by other disturbing symptoms, it could point to a dangerous infection and must be looked into. And in these cases, the temperature, whether high or low, isn’t necessarily indicative of the extent or severity of the illness. The other symptoms turn out to be more important in these cases. How long you’ve had a fever will also count.

A serious fever is one in which the body temperatures rise to 41°C (105.8°F). This is dangerous and may cause damage to the body. At such high temperatures most organs malfunction and may ultimately fail. Such a high core temperature is rare in itself. They are sometimes caused by very severe infections like sepsis, malaria, or meningitis. Certain illicit drugs (such as cocaine, amphetamines, or phencyclidine), anesthetics, and antipsychotic drugs can also trigger extremely high temperatures. But very high core temperature or hyperthermia is more typically caused by heat fatigue, heat syncope (sudden dizziness after prolonged exposure to the heat), heat cramps, heat exhaustion, and heat stroke.

But remember there’s a distinction here: high fevers may be a form of hyperthermia, but they aren’t an uncontrolled shooting up of temperature (as is the case in instances like heatstroke).6 Instead, a fever is a more controlled, regulated rise in temperature. Kind of like a thermostat that your body is using to control core temperature.7

When Should You Go To The Doctor?

The National Health Service UK recommends that if your child is under three months old and has a temperature of 38°C (101°F) or above; or is between three and six months old and has a temperature of 39°C (102°F) or above; or is showing other signs of being unwell, such as persistent vomiting, refusal to feed, floppiness, or drowsiness, you should seek urgent medical help.8

People with a heart, or lung disorder, or dementia are considered to be at risk of dangerous complications when they get a fever so they shouldn’t take chances.

According to the Merck Manual a fever should also be looked at by a doctor immediately if it is accompanied by other symptoms like:

  • a change in mental function, such as confusion
  • a headache, stiff neck, or both
  • flat, small, purplish red spots on the skin, which indicate bleeding under the skin
  • low blood pressure
  • rapid heart rate or rapid breathing
  • shortness of breath

In any case, you should go to the doctor if your fever lasts for more than three or four days.9

Don’t Worry, Stay Hydrated

Serious causes of fever are relatively rare. So if you have a slight fever then there’s usually no cause for worry. Your doctor may recommend an over-the-counter medicine to bring down a high fever. Remember to drink a lot of fluids so that you stay hydrated.

References   [ + ]

1.Svoboda, Robert. Ayurveda: Life, health and longevity. Penguin Books India, 1992.
2.Longo, Dan L., Anthony S. Fauci, Dennis L. Kasper, Stephen L. Hauser, J. Larry Jameson, and Joseph Loscalzo. Harrison’s Principles of Internal Medicine 18E Vol 2 EB. McGraw Hill Professional, 2012.
3.Loscalzo, Joseph; Fauci, Anthony S.; Braunwald, Eugene; Dennis L. Kasper; Hauser, Stephen L; Longo, Dan L. (2008). “Chapter 17, Fever versus hyperthermia”. Harrison’s principles of internal medicine. McGraw-Hill Medical.
4, 5.Fever, US National Library of Medicine.
6.Stitt, John T. “Fever versus hyperthermia.” InFederation proceedings, vol. 38, no. 1, pp. 39-43. 1979.
7.Richardson, Martin, and Ed Purssell. “Who’s afraid of fever?.” Archives of disease in childhood 100, no. 9 (2015): 818-820.
8.Fever in Children, NHS UK.
9.Albert, Richard K. The Merck manual home health handbook. Edited by Robert S. Porter, Justin L. Kaplan, and Barbara P. Homeier. Merck & Company, 2009.
CureJoy Editorial

The CureJoy Editorial team digs up credible information from multiple sources, both academic and experiential, to stitch a holistic health perspective on topics that pique our readers' interest.

CureJoy Editorial

The CureJoy Editorial team digs up credible information from multiple sources, both academic and experiential, to stitch a holistic health perspective on topics that pique our readers' interest.