Fever is one of the most common experiences in the life of practically every human being with time to develop, and is linked to a wide variety of health disorders. That is why it is important to understand this phenomenon and know how to identify the types of fever that exist.
In this article We will see what types of fever exist according to different classifications, and as well as their characteristics and possible health hazards.
What is fever?
Fever, an increase in body temperature, occurs as a reaction of the body to an agent identified as a pathogen in order to eliminate it and activate the immune system.
Thus, fever acts as a sign that tells us that something is not going well in our body and also encourages the non-proliferation of germs, since these normally only grow at normal temperatures between 35.5 and 37 °C; We will consider fever when the temperature is higher than 38 °C, and this will be considered urgent when it exceeds 41 °C. Seen another way, it is considered that the normal temperature of the human body ranges from 35.5 to 37 °C, and may vary depending on the subject.
Thus, Temperatures between 37 and 38 °C constitute what is known as low-grade fever when it is maintained for 24 hours. If it is higher than 38 °C, it is considered a fever. At 39 °C, the fever is classified as moderate, and at 40 °C, it already indicates an emergency situation.
We say that an individual has a fever when we observe an increase in body temperature, hyperthermia; this occurs in the presence of a possible pathogenic agent, usually an infection This increase in temperature tells us that our immune system has been put into operation to combat these elements that have “snuck in” into the body; Therefore, it works as an alarm to act if we see that this feverish state does not improve, and also as a defensive mechanism to kill certain harmful microbes.
The characteristic symptoms of fever are: headache, muscle pain, chills and drowsiness. In general a feeling of tiredness and exhaustion arises
Types of fever (classified and explained)
There are different types of fever that we will classify according to their intensity, duration, temporal pattern, what cause they have and how they started. We have already introduced the classification of fever according to intensity in the previous section. We have: low-grade fever if the temperature is 37 to 38 °C, fever of 38 to 41 °C, and hyperpyrexia if it exceeds 41 °C.
Fever is a common symptom that often indicates an underlying condition, such as an infection, inflammation, or another medical issue. It is defined as an increase in body temperature above the normal range (typically around 98.6°F or 37°C). The body’s temperature regulation system, controlled by the hypothalamus, responds to various triggers, and the fever can vary depending on the type of illness or condition causing it.
In this article, we will explore the 14 types of fever based on their characteristics and body temperature levels, helping you better understand what might be going on in your body.
1. Continuous Fever
Continuous fever, also known as sustained fever, occurs when a person’s body temperature remains consistently high (above 100.4°F or 38°C) for an extended period without a significant fluctuation. This type of fever is often associated with infections like typhoid fever or pneumonia.
- Body temperature range: Typically remains above 100.4°F (38°C) without dropping below normal.
- Causes: Bacterial infections, like typhoid fever, pneumonia, or brucellosis.
2. Intermittent Fever
Intermittent fever is characterized by periodic rises in body temperature, often returning to normal levels between fever episodes. It can be a sign of several conditions, including malaria, sepsis, or tuberculosis.
- Body temperature range: Fever rises above 100.4°F (38°C) intermittently, with periods of normal or subnormal temperatures.
- Causes: Malaria, sepsis, or pyogenic infections.
3. Remittent Fever
Remittent fever is a type of fever where the temperature fluctuates but never returns to normal. This fever is often seen in conditions such as bacterial infections, rheumatic fever, or infective endocarditis.
- Body temperature range: Above 100.4°F (38°C), fluctuating but remaining elevated.
- Causes: Bacterial infections, endocarditis, or rheumatic fever.
4. Relapsing Fever
Relapsing fever is marked by periods of high fever followed by a period of normal temperature, only to have the fever return again after a few days. This type of fever is most commonly associated with Borrelia bacterial infections, such as tick-borne relapsing fever.
- Body temperature range: A cycle of fever spikes and periods of normal or lower-than-normal temperatures.
- Causes: Borrelia infections (relapsing fever) or Louse-borne typhus.
5. Septic Fever
Septic fever occurs when the body is fighting an infection, especially one that has spread throughout the bloodstream (sepsis). This fever is typically accompanied by other signs of infection, such as a rapid heart rate, chills, and low blood pressure.
- Body temperature range: Higher than 101°F (38.3°C), may fluctuate.
- Causes: Sepsis, bacterial infections, or bloodstream infections.
6. Fever of Unknown Origin (FUO)
This term refers to a fever that lasts for more than three weeks, and despite repeated tests, the cause remains undiagnosed. It can be caused by a wide variety of conditions, such as autoimmune diseases, malignancies, or chronic infections.
- Body temperature range: Sustained temperature of more than 100.4°F (38°C) for an extended period.
- Causes: Autoimmune diseases, malignancies, or undiagnosed infections.
7. Hyperpyrexia
Hyperpyrexia is an extremely high fever that exceeds 106°F (41.1°C). This is considered a medical emergency and can lead to severe complications such as brain damage if not treated promptly. It may occur due to heatstroke, infection, or drug-induced fever.
- Body temperature range: Above 106°F (41.1°C).
- Causes: Heatstroke, severe infections, or drug-induced fever.
8. Low-Grade Fever
A low-grade fever typically refers to a mild increase in body temperature, usually between 99°F and 100.4°F (37.2°C – 38°C). It is often a sign of a mild infection or inflammatory conditions.
- Body temperature range: 99°F to 100.4°F (37.2°C – 38°C).
- Causes: Common cold, minor infections, or mild inflammation.
9. High Fever
High fever is characterized by a body temperature above 103°F (39.4°C). It often indicates a more serious infection, such as influenza, bacterial pneumonia, or severe viral infections.
- Body temperature range: Above 103°F (39.4°C).
- Causes: Flu, severe bacterial infections, or malaria.
10. Chill Fever
Chill fever is marked by shivering or chills followed by an increase in body temperature. This type of fever is often caused by infections, such as malaria, sepsis, or pneumonia.
- Body temperature range: Fever follows a chilling or shivering period, usually above 100.4°F (38°C).
- Causes: Malaria, sepsis, or pneumonia.
11. Postoperative Fever
Fever that occurs after surgery, known as postoperative fever, can arise from infection, inflammation, or as a normal response to surgical trauma. In some cases, it’s part of the healing process, but in others, it may indicate infection or complications.
- Body temperature range: Elevated body temperature above 100.4°F (38°C).
- Causes: Infections, surgical trauma, or inflammatory response.
12. Drug-Induced Fever
Certain medications can cause the body’s temperature to rise as a side effect, leading to drug-induced fever. This may happen due to a reaction to medications like antibiotics, anti-seizure drugs, or anti-inflammatory drugs.
- Body temperature range: May rise above 100.4°F (38°C), depending on the drug.
- Causes: Medications, drug reactions.
13. Fever in Children
Children tend to experience higher fevers than adults. A fever in children is typically defined as a temperature above 100.4°F (38°C) and can be caused by a range of viral or bacterial infections.
- Body temperature range: Above 100.4°F (38°C).
- Causes: Common cold, ear infections, viral infections.
14. Night Fever
Night fever is characterized by high fever that occurs only during the night and may be caused by a variety of factors, such as infections, inflammatory diseases, or autoimmune conditions. It is often accompanied by chills or sweats.
- Body temperature range: Increases at night, often above 100.4°F (38°C).
- Causes: Infections, autoimmune diseases, or inflammatory conditions.
By understanding the different types of fever, their body temperature levels, and their potential causes, you are better equipped to recognize when to seek medical attention. Fever is a symptom, not a disease itself, and the underlying cause needs to be identified and treated for a full recovery.
FAQs About Fever
What is a normal body temperature?
A normal body temperature typically ranges from 97°F to 99°F (36.1°C – 37.2°C). Anything above 100.4°F (38°C) is considered a fever.
When should you seek medical attention for a fever?
You should seek medical attention if the fever exceeds 103°F (39.4°C), if you experience difficulty breathing, persistent vomiting, severe headache, or rash. In children, seek immediate medical advice for fevers over 100.4°F (38°C) that persist for more than a few days.
Can a fever be harmful?
If a fever exceeds 104°F (40°C) for an extended period, it can be dangerous and lead to complications like seizures, dehydration, or even brain damage. High fever should be treated promptly.
What causes low-grade fever?
Low-grade fever is often caused by mild viral infections, such as the common cold or flu. It can also result from inflammatory conditions or autoimmune diseases.
How can I reduce a fever at home?
To reduce a fever, you can try drinking plenty of fluids, resting, taking cool baths, or using fever-reducing medications like acetaminophen or ibuprofen. However, if the fever is persistent or very high, seek medical advice.
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PsychologyFor. (2025). The 14 Types of Fever (And Body Temperature Levels). https://psychologyfor.com/the-14-types-of-fever-and-body-temperature-levels/