Fever: Types, Causes, Symptoms, and Treatment


What is fever?

Fever is a common medical sign and is often a natural response of the body’s immune system to an infection or illness. While fever can be a cause for concern, especially in infants and young children, it is important to understand that fever is not always an indicator of a serious underlying condition. In fact, treating a fever does not necessarily improve the outcome of the illness or infection.

The fear and anxiety that often accompanies fever, known as “fever phobia,” can cause unnecessary stress for both patients and healthcare providers. It is important to understand the causes and symptoms of fever and to seek medical attention if necessary, but also to avoid unnecessary worry and panic.

How is body temperature measured properly?

Various types of thermometers are available to measure body temperature, including oral, rectal, ear (tympanic), and forehead (temporal artery) thermometers.

Oral and rectal thermometers are typically considered the most precise tools for measuring core body temperature. In contrast, ear or forehead thermometers, while more convenient to use, tend to provide less accurate temperature readings.

For infants, a rectal thermometer is generally considered to be the most accurate option. Please always mention the type of thermometer used when reporting a temperature to your physician, along with the temperature reading itself.

What is considered a normal body temperature?

Among healthy adults, the typical range for oral temperature is 35.7–37.7 °C (96.3–99.9 °F) for men and 33.2–38.1 °C (91.8–100.6 °F) for women. Rectal temperature ranges from 36.7–37.5 °C (98.1–99.5 °F) for men and 36.8–37.1 °C (98.2–98.8 °F) for women, while ear measurement ranges from 35.5–37.5 °C (95.9–99.5 °F) for men and 35.7–37.5 °C (96.3–99.5 °F) for women.

Several factors affect normal body temperature, such as age, sex, time of day, activity level, and surrounding temperature. A slight daily variation in body temperature is typical, which is usually 0.5 °C (0.9 °F).

Not every elevated temperature is a fever. For instance, when people exercise, their temperature increases, but it is not considered a fever since their set point is normal. In contrast, a “normal” temperature may be a fever if it is unusually high for that individual. For example, elderly individuals who are medically frail may have a decreased ability to produce body heat, so a “normal” temperature of 37.3 °C (99.1 °F) could indicate a significant fever.

Fever signs and symptoms

Individual body temperatures can vary slightly and may also fluctuate throughout the day. Historically, the average body temperature has been considered to be 98.6 °F (36.6 °C). However, a temperature reading of 100 °F (37.8 °C) or higher, obtained using an oral thermometer, is generally considered to indicate a fever.

In addition to an elevated temperature, a fever may also cause other symptoms, depending on its underlying cause. Some common fever signs and symptoms include sweating, chills and shivering, headache, muscle aches, loss of appetite, irritability, dehydration, and general weakness.

How is fever triggered?

The body’s typical temperature is maintained by a delicate balance between heat production and heat loss. The hypothalamus, a region of the brain often referred to as the body’s “thermostat,” is responsible for monitoring and regulating this balance. Even in a healthy state, the body temperature can fluctuate slightly throughout the day, typically being lower in the morning and higher in the late afternoon and evening.

When the immune system detects an infection, the hypothalamus can trigger a fever response, raising the body temperature. This process involves complex mechanisms that generate more heat and limit heat loss. Shivering is one method the body employs to generate heat, while covering oneself with a blanket helps retain body heat.

In cases of common viral infections such as the flu, fevers up to 104 °F (40 °C) can aid the immune system in fighting the disease and are generally not harmful.

Types of fever

There are several types of fever, classified based on their duration and pattern:

  1. Acute fever: This is the most common type of fever, lasting for less than seven days. It is usually caused by infections, such as the flu or a cold.
  2. Subacute fever: This type of fever lasts for one to two weeks and is often caused by infections, such as tuberculosis or endocarditis.
  3. Chronic fever: This type of fever lasts for more than two weeks and may be caused by a wide range of conditions, such as autoimmune disorders, cancers, and infections like HIV.
  4. Remittent fever: This is a fever that remains elevated throughout the day but fluctuates by more than one degree Celsius over 24 hours.
  5. Intermittent fever: This is a fever that alternates between periods of fever and normal temperature, with each period lasting for several hours.
  6. Pel-Ebstein fever: This is a rare type of fever that occurs in some people with Hodgkin’s lymphoma. It is characterized by a fever that lasts for about one week, followed by a fever-free period of about one week.
  7. Hectic fever: This is a fever that has a wide fluctuation in temperature, often exceeding 39°C (102.2°F) and with a range of more than 2°C (3.6°F) between the peak and the trough. It is often seen in severe infections, such as sepsis.

What are the usual causes of fever?

An elevated body temperature or fever can be caused by various factors, including:

  • Viral infections
  • Bacterial infections
  • Heat exhaustion
  • Certain inflammatory conditions, such as rheumatoid arthritis
  • Malignant tumors (cancer)
  • Some medications, such as antibiotics, drugs used to treat high blood pressure or seizures
  • Certain immunizations, such as the diphtheria, tetanus and acellular pertussis, pneumococcal, or COVID-19 vaccine

If you are concerned about a fever or elevated body temperature, call your doctor. He/she can help determine the underlying cause and recommend appropriate treatment options.

Can gastroenteritis cause fever?

Yes, gastroenteritis can cause fever. Gastroenteritis, also known as stomach flu, is an inflammation of the gastrointestinal tract that can be caused by a virus, bacteria, or parasite. In addition to symptoms such as nausea, vomiting, and diarrhea, gastroenteritis can also cause fever.

Fever is a common symptom of viral gastroenteritis and is usually mild, ranging from 99°F to 101°F (37.2°C to 38.3°C). Bacterial gastroenteritis can also cause fever, which is often higher and more persistent than in viral cases.

If you suspect you have gastroenteritis, it is important to stay hydrated and seek medical attention if your symptoms are severe or persistent.

What natural remedies can I use to reduce fever?

While natural remedies may help in reducing fever, keep in mind that a fever is usually a sign of an underlying illness or infection and treating the underlying condition is the most effective way to reduce fever. However, here are some natural remedies that may help in reducing fever:

  1. Stay hydrated: Drinking plenty of fluids can help reduce fever and prevent dehydration. Water, herbal teas, clear soups, and electrolyte solutions are all good choices.
  2. Rest: Resting is important to help your body recover from illness and reduce fever.
  3. Apply cool compresses: Placing cool, damp washcloths on your forehead, wrists, and ankles may help reduce body temperature.
  4. Take a cool bath: Taking a cool bath or shower can help reduce fever by lowering your body temperature.
  5. Use essential oils: Some essential oils, such as peppermint and eucalyptus, have cooling properties and can be used in a diffuser or diluted in a carrier oil and applied to the skin to help reduce fever.
  6. Ginger: Ginger has anti-inflammatory properties and may help reduce fever. You can drink ginger tea or add ginger to your meals.

If your fever is high or persistent, it’s important to seek medical attention and follow your doctor’s recommendations.

When should I call my doctor?

You should contact your doctor if your temperature rises to 103 °F (39.4 °C) or higher. Additionally, seek immediate medical attention if you experience any of the following symptoms along with a fever:

  • Severe headache
  • Persistent vomiting
  • Abdominal pain
  • Convulsions or seizures
  • Mental confusion, strange behavior, or altered speech
  • Pain when urinating
  • Rash
  • Unusual sensitivity to bright light
  • Stiff neck and pain when you bend your head forward
  • Difficulty breathing or chest pain

What can I do to prevent an infection and reduce the risk of fever?

To reduce the risk of fevers caused by infectious diseases, there are several steps you can take to minimize exposure to viruses and bacteria:

  1. Get vaccinated for recommended infectious diseases
  2. Follow public health guidelines for wearing masks and social distancing to minimize contact with others who may be sick
  3. Wash your hands frequently, especially before eating, after using the toilet, after being in a crowd or around someone who is sick, after petting animals, and during travel on public transportation
  4. Teach children how to wash their hands thoroughly, covering both the front and back of each hand with soap and rinsing completely under running water
  5. Carry hand sanitizer with you when soap and water are not available
  6. Avoid touching your nose, mouth, or eyes, as these are the primary ways viruses and bacteria enter your body and cause infection
  7. Cover your mouth when you cough and your nose when you sneeze, and teach your children to do the same. Whenever possible, turn away from others and cough or sneeze into your elbow to avoid passing germs along to them
  8. Avoid sharing cups, water bottles, and utensils with others, especially children

By following these practices, you can help reduce the likelihood of getting sick and experiencing a fever.

How can I contact gastroenterologist Dr. Zavos for an appointment?

Dr. Chris Zavos is a board-certified gastroenterologist and hepatologist, located in Thessaloniki Greece, and specifically in Kalamaria suburb, about 7 kilometres (4 miles) southeast of downtown Thessaloniki. His private office is at: Fanariou 8 street (near Aigaiou and Adrianoupoleos avenues), Kalamaria (Thessaloniki), Greece.

Thessaloniki International Airport is only 10 km away from his private office in Kalamaria and can be reached by taxi within 13 minutes from the airport.

Dr. Chris Zavos performs endoscopies at Bioclinic private hospital in downtown Thessaloniki (Mitropoleos 86 street).

You can contact Dr. Zavos at phone numbers: (+30)-6976596988 and (+30)-2311283833, or you can email him at czavos@ymail.com. Dr. Zavos responds to Greek and English languages.

Last update: 26 September 2023, 18:56


Gastroenterologist - Hepatologist, Thessaloniki

PhD at Medical School, Aristotle University of Thessaloniki, Greece

PGDip at Universitair Medisch Centrum Utrecht, The Netherlands

Ex President, Hellenic H. pylori & Microbiota Study Group