Internal Fever: What Is It, Symptoms & What To Do

In cases of 'internal fever' you can feel very hot but the thermometer does not show this rise in temperature. The most common situation is that a person has the same symptoms as a real fever, such as malaise, chills and a cold sweat, but the thermometer is still at 36 to 37 °C, which does not indicate fever.

Although you may complain that your body feels very hot, in fact, the 'internal fever' does not exist, it is just a popular way of expressing that you have  the same symptoms as a normal fever, but the degree of the fever is not felt on the palm of your hand, nor is it verified by a thermometer.

Internal Fever: What Is It, Symptoms & What To Do

Main symptoms of a common fever

In a common fever, in addition to your temperature rising above 37.5 ºC, there are symptoms such as:

  • Feeling hot;
  • Cold sweats;
  • Chills or shivers throughout the day;
  • Malaise;
  • Headache;
  • Tiredness;
  • Lack of energy.

However, in cases of ‘internal fever’, although all these symptoms are present, there is no rise in temperature that can be measured.

What a fever can indicate

Fever is a response of the body in order to fight harmful microorganisms by raising its temperature, being a natural reaction in cases of infections caused by viruses, fungi, bacteria or parasites. So, a fever is not a disease, it is just a symptom that is associated with many types of diseases and infections.

Fever is only really harmful when it gets above 40 °C, which can happen quickly, especially in babies and children, and can cause seizures.

A mild fever is considered to be up to 38 °C, considered as just a rise in temperature, or simply a feverish state, and not very serious, indicating only that you may need to be alert and take off excess clothing to try to cool your body down to normal temperature, which is about 36º C. Fever above 38.5º C may indicate the need to take fever-lowering medication, as well as other natural methods to normalize body temperature.

The 'thermostat' that controls body temperature is the hypothalamus, which is very sensitive to any temperature change. It can cause the body to produce more heat, which is dissipated through the skin, so whenever there is a real rise in temperature, the thermometer is able to indicate this fact. So, it can be concluded that 'internal fever’ does not exist.

What to do in case of 'internal fever'

When you think you have an 'internal fever' you should take a warm bath and lie down and rest. Often the cause of this fever sensation is stress and anxiety attacks, which can also cause tremors throughout the body.

The taking of fever-lowering medication, such as acetaminophen or ibuprofen, is only recommended under medical advice and when the thermometer registers at least 38.5 °C. If, as in the case of 'internal fever’, the thermometer does not show this temperature, no medication should be taken to try to fight a fever that does not exist. So, if necessary, you should just take off your excess clothes and take a bath in warm water to try to lower body temperature and alleviate discomfort.

If symptoms persist, you should see your doctor for a physical exam to find out what may be happening. In addition to blood and urine tests, your doctor may also order a chest X-ray, for example, to check for any lung changes that may be causing this sensation of fever.

Possible causes of 'internal fever'

Emotional causes, such as a stress or anxiety crisis, and women's ovulation during the fertile phase are the main causes of internal fever. However, you may also find that you have a fever after exercising or some kind of physical exertion, such as carrying heavy bags or climbing a flight of stairs. In this case, the temperature usually returns to normal after a few minutes’ rest.

At the onset of a cold or the flu, feeling unwell, tiredness and heaviness in the body are common, and sometimes people refer to a feeling of 'internal fever’. In this case, taking a home remedy such as warm ginger tea may be a good way to feel better.

Can 'internal fever' be a sign of COVID-19?

'Internal fever' can happen when the body tries to fight an infection, appearing as a first sign before a real fever. Therefore, it is possible that some people infected with COVID-19 may experience an internal fever before any other symptoms.

It is then recommended to observe other symptoms that may appear and that are more indicative of infection by the new coronavirus, such as dry cough, excessive tiredness, loss of taste and smell, or fever.

When to go to the doctor

It is recommended you seek medical help when, in addition to the sensation of internal fever, you have other symptoms such as:

  • Sneezing, coughing;
  • Vomiting, diarrhea;
  • Mouth sores;
  • Rapid temperature rises to above 39º C;
  • Fainting or decreased attention span;
  • Bleeding through the nose, anus or vagina, with no apparent explanation.

In this case, it is still important to tell the doctor all the symptoms you have, when they appeared, if you changed something in your diet or if you were in another country, for example. If there is pain, it is still advisable to explain which part of the body is affected, when it started and if the intensity has been constant.

With this information the doctor may suspect a disease and request tests if necessary, indicating the most appropriate treatment.

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  • MEDLINE PLUS - U.S. NATIONAL LIBRARY OF MEDICINE. Chills. Available on: <>. Access in 21 Jun 2021
  • CENTERS FOR DISEASE CONTROL AND PREVENTION. Symptoms of COVID-19. 2021. Available on: <>. Access in 21 Jun 2021
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