An “internal fever” occurs when you feel very hot but the thermometer shows a temperature within a normal range. You may have symptoms very similar to a fever (such as general malaise, chills and cold sweats), however the thermometer remains at 36 to 37°C, which is considered a normal range.
An “internal fever” is not an actual medical condition. Although you may indeed feel warm, it is just a colloquial way of expressing you have the same symptoms as a normal fever without a measurable rise in temperature.
Possible causes of an “internal fever”
An “internal fever” can be caused by drastic changes to emotions (e.g. stress or anxiety) and can also occur during the ovulation phase of a woman's menstrual cycle. It is also commonly felt after exercising or excessive physical exertion (e.g. carrying heavy bags or climbing a flight of stairs). After physical activity, body temperature usually returns to normal after a few minutes of rest.
At the onset of a cold or the flu, feeling unwell, feeling tired and overall heaviness are common, and the feeling of an “internal fever” can also emerge. Warm ginger tea is an excellent home remedy to aid in these specific symptoms.
Can “internal fever” be a sign of COVID-19?
An “internal fever” can happen when the body tries to fight off an infection, and can appear before a real fever emerges. It is possible that some people infected with COVID-19 may experience an “internal fever” before any other symptoms.
If you feel an “internal fever” coming on, you should monitor for any other new symptoms, especially those that are indicative of COVID-19 (e.g. a dry cough, excessive tiredness, loss of taste and smell, or fever).
What to do if You have “internal fever”
If you think you have an “internal fever,” a warm bath, removing excess clothing and rest is advised. Oftentimes, the cause of this fever sensation is due to stress or an anxiety attack, both of which can also cause tremors throughout the body.
Taking antipyretics, such as acetaminophen or ibuprofen, is only recommended under medical advice and when you have a temperature of at least 38.5°C. With an “internal fever,” the thermometer does not show a rise in temperature, and therefore medication is generally not indicated.
If symptoms persist, however, 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 imaging tests (e.g. a chest x-ray to check for any lung changes that may be causing this sensation of a fever).
How to identify an "actual" fever
A fever is typically defined by a temperature exceeding 37.5 ºC. Other symptoms that can accompany a fever include:
- Feeling hot
- Cold sweats
- Chills or shivers throughout the day
- General malaise
- Lack of energy
In cases of an “internal fever,” all of these symptoms may be present, however there is no measurable rise in temperature.
What a fever means
A fever is a physiologic response employed by the body to fight off harmful microorganisms. By raising its temperature, the body can naturally protect and treat infections caused by viruses, fungi, bacteria or parasites. Therefore, a fever is not a disease, but rather just a symptom that is associated with many types of diseases and infections.
A fever is only really harmful when it exceeds 40 °C, but this can happen very quickly (especially in babies and children) and can cause seizures.
A mild fever is considered to be a temperature that rises up to 38°C and is typically not very serious. You may need to monitor your temperature and try to cool your body down to normal temperatures (around 36ºC) by taking off any excess clothing. With a fever above 38.5ºC, antipyretics (fever-lowering medication) may be indicated in conjunction with other natural methods to lower a high temperature.
The hypothalamus, also known as the body's thermostat, controls body temperature and is very sensitive to temperature changes. It can cause the body to produce more heat by signaling the muscles to tremor or "shiver" or send signals to your sweat glands to cool off. With a fever, the hypothalamus will set the body to a higher temperature to help combat infection.
When to go to the doctor
It is recommended that you seek medical help when in addition to the sensation of an “internal fever,” you have other symptoms such as:
- Sneezing or coughing
- Vomiting or diarrhea
- Cold sores
- Rapid temperature rises that exceed 39ºC
- Fainting or decreased level of consciousness
- Bleeding from the nose, anus or vagina with no apparent explanation
It is very important to discuss all the symptoms you have with your doctor, making sure to communicate when they first appeared, if you changed anything in your diet, or if you were recently in another country. If you are also experiencing pain, be sure to explain which part of the body is affected, when the pain started and if the intensity has been constant.
Having sufficient information can prompt your doctor to evaluate your condition thoroughly and indicate the most appropriate treatment.