Chills but no fever describes the experience of shivers and feeling warm without an elevated core temperature. This is sometimes referred to as an “internal fever”, as your external body temperature is normal, however internally your body may feel warmer than usual and cause physical symptoms.

You may have fever-like symptoms with this phenomena, such as general malaise, chills and cold sweats), however the thermometer remains at 36 to 37°C, which is considered a normal range.

Having chills but no fever, or 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

Chills with no fever can occur for the following reasons:

1. Changes to emotions

Very intense emotions, like fear, anxiety or even strong pleasure and arousal, can lead to chills but no fever. Some people may describe this type of reaction as a "shiver down the spine" and may visibly see goosebumps on their extremities. This is considered to be a response to a psychologically significant event and resolves once the emotion has subsided.

2. Ovulation

Ovulation usually triggers a higher level in progesterone levels, which raise your body’s core temperature. This mild increase can make women more sensitive to cold environments, prompting chills or shivers but not a fever.

3. Physical activity

Long or intense exercise can also raise your body’s core temperature and keep it increased throughout the duration of the activity. This prompts your body to produce sweat to cool down. Moisture on the skin’s surface that is exposed to a draft or cold environment following exercise can stimulate chills, but this moisture does not induce a fever.

4. Infection

When the body is fighting a viral or bacterial infection, the immune system promotes various defense mechanisms to attack foreign invaders systemically. One of these mechanisms is chills or shivers, which increase the body’s temperature to help eliminate the virus or bacteria. Many people also experience muscle achiness as a result.

5. After eating

Many people report symptoms of "postprandial syndrome" after eating. This condition is characterized by an increase in sympathetic nervous activity after eating a meal without a direct or measurable change in blood sugar levels. Chills or tremors may be experienced after eating, as well as sweating, anxiety or palpitations.

6. Cold environment

When exposed to a cold environment, the body responds involuntarily in the form of chills. Shivering from the cold is a natural mechanism that employs skeletal muscle activity in order to increase body heat and temperature.

7. Hypothyroidism

Hypothyroidism is a condition characterized by an underactive thyroid, or a thyroid that does not produce sufficient thyroid hormones. It slows down metabolism, which can lead to a decrease in core body temperature. This prompts the body to tremble or to have chills, as a way to warm up and maintain body heat.

8. Low blood sugar

Hypoglycemia can promote the release of epinephrine and norepinephrine as an attempt for cells to regain energy when glucose levels are low. These hormones cause shakiness, chills or trembling, as well as sweating, confusion or restlessness.

9. Low body weight

People with a low body weight will generally have less fat tissue to insulate. This can make you more prone to feeling changes or fluctuations in temperatures, leading to chills.

Can chills but no 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).

How to treat

If you experience chills and have a normal temperature, 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
Headache
Tiredness
Lack of energy

In cases of an “internal fever,” all of these symptoms may be present, however there is no measurable rise in temperature. Read more about how to identify a fever.

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

If you experience chills with no fever, you should see a doctor, especially if 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.