Fever In Adults When to Worry

General definition: what is fever in adults

Fever is a temporary condition that can develop as a result of a disease or infection in the individual's body. It is also known as high temperature or high body temperature. 1 Fever is not usually a cause for concern, even if it causes discomfort in the body. However, it is recommended to be aware of the symptoms accompanying fever and to consult a doctor when necessary. One way to think of fever is an indication that the body's immune system fighting or reacting to the body’s infection. A person's normal body temperature is determined by a part of the brain called the hypothalamus. The body temperature regulation center in the hypothalamus pulls the body temperature settings to the upper levels when an unexpected situation occurs in the body. 2 

Each person's body temperature may be different. The average body temperature of an individual is usually 37°C (98.6 °F). However, when you take your temperature more than once during the day, it is normal to see minor changes because the body temperature often change throughout the day. If your body temperature is higher than 38°C (100°F) when you take it, you might have a fever. 3 Although it is quite common and normal to experience body discomfort in fever (high body temperature), it is best to consult a doctor for better diagnosis and treatment.


There are many symptoms that can accompany or be caused by fever in the body, most common ones are listed below:

  • Feeling cold
  • Sweating
  • Chills
  • Shivering
  • Irritability
  • Headache
  • Sweating
  • Experiencing weakness on the body
  • Tiredness
  • Increased pain sensitivity
  • Body pain (muscle pain, joint pain, constipation pain, spine pain)
  • Difficulty in focusing / Concentration issues
  • Acceleration in heartbeat

If you experience shivering and sweating when your temperature is below 38°C (100°F) or your body temperature goes up and down, you may still have a fever. Please consult your doctor. 


Many different diseases can cause fever. Most common reason of the fever (high body temperature) is infections that causes diseases such as flu. Most common conditions and diseases known to might cause fever are listed below:

  • Respiratory tract infections
  • Fungal infections
  • Bacterial or viral infections
  • Food poisoning
  • Inflammation
  • Hot Stroke and/or Sunburn
  • Infections due to insect bites
  • Hyperthyroidism
  • Autoimmune diseases
  • Some types of cancer
  • Tumors
  • Some medications and treatments

When to worry?

Even though adults frequently experience a mild fever, this is not a cause for an alarm. In addition to the fever, the person's body must be examined for any additional accompanying symptoms. Adult fever brought on by infectious diseases quickly goes away. Additionally, if the person experiences fever-related discomfort, it can be easily managed with the help of fever suppressant drugs.

If any of the following symptoms occur, it is advised to see a doctor:

  • Fever in adults lasting more than 3 days
  • Hotstroke
  • Ineffectiveness of fever-reducing drugs 
  • Confusion
  • Muscle cramps / severe pain of the muscles
  • Dehydration
  • Stomach ache
  • Stiffness and pain in the neck
  • High sensitivity to light

People already sufering with long-term diseases such as asthma, diabetes, anemia, cardiovascular diseases, liver diseases, kidney diseases, chronic lung diseases, cerebral palsy, multiple scoliosis, autoimmune diseases and HIV-AIDS should be more careful if they experience fever (high body temperature). 

Measuring the fever in the most accurate way step by step

You can measure your temperature accurately by following the guide below:

  1. Make sure turn off the thermometer.
  2. Clean the tip of the thermometer with soap and water.
  3. Rinse the tip of the thermometer with water and dry it.
  4. Turn on the thermometer.
  5. Place the tip of the thermometer under your tongue (at the back of your mouth) or under your armpit.
  6. Wait until the thermometer signals / sounds.
  7. Check the reading on the thermometer.

If the value you see on the thermometer is higher than 38°C (100°F), you have a fever. Make sure you take the necessary precautions and drink plenty of fluids.


Since fever occurs as the result of another disease, its treatment may vary according to the disease causing the fever. It is important to bring down the fever (high body temperature) so that the body's organs and tissues don't become damaged.

  • Drink lots of fluids (especially water)
  • Have a balanced and healthy diet
  • Get enough sleep and rest well
  • Take a shower with warm water
  • Lower the room temperature
  • Apply cold compresses to the underarm / armpit area 
  • Get fresh air
  • Ventilate your home regularly
  • Take fever suppressant

Fever lasting more than 3 days in adults might be caused by an important medical situation and it may require medical treatment by a doctor.


Fever (high body temperature) can also occur as one of the symptoms of COVID-19. If you have symptoms such as 

  • constant cough 
  • loss of taste and/or smell 
  • pain in the body 
  • sore throat 
  • shortness of breath 
  • diarrhea 
  • running nose and/or blocked nose 
  • loss of appetite accompanying fever

It is recommended that you consult a doctor and have a COVID test. If you have one or more of these symptoms, don't leave the house until you know your COVID test result is negative. 4


Fever is a temporary condition that occurs due to an infection or disease in the body and creates a feeling of discomfort in the body. Mostly, the cause might be infection-based diseases, but also there are many other diseases that might cause fever. In adults, a body temperature more than 38° C (100° F) is considered a fever. 

In addition to fever, it is usually quite common to experience symptoms such as feeling cold, sweating, chills, shivering, irritability, headache, experiencing weakness on the body, tiredness, increased pain sensitivity, body pain (muscle pain, joint pain, constipation pain, spine pain), difficulty in focusing / concentration issues, acceleration in heartbeat. However, if you are also experiencing fever lasting more than 3 days, hotstroke, ineffectiveness of fever-reducing drugs, confusion, muscle cramps / severe pain of muscles, dehydration, stomach ache, stiffness and pain in the neck, high sensitivity to light as an adult, you should see a doctor. The best methods for home treatment are to drink plenty of water, take a warm shower, ventilate the house, rest, get quality sleep and, if necessary, take fever-reducing medications.


  1. NHS. 2020a. “High Temperature (Fever) in Adults.” Nhs.uk. April 6, 2020. https://www.nhs.uk/conditions/fever-in-adults/.
  2. Harvard Medical School. 2018. “Fever.” Harvard Health Publishing. October 26, 2018. https://www.health.harvard.edu/a_to_z/fever-a-to-z#:~:text=Fever%20develops%20when%20the%20hypothalamus.
  3. Mayo Clinic. 2017. “Fever - Symptoms and Causes.” Mayo Clinic. 2017. https://www.mayoclinic.org/diseases-conditions/fever/symptoms-causes/syc-20352759.
  4. NHS. 2020b. “Symptoms of Coronavirus (COVID-19).” Nhs.uk. June 2, 2020. https://www.nhs.uk/conditions/coronavirus-covid-19/symptoms/main-symptoms/.
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Sena Kaptan

Clinical Psychology and Mental Health MSc, Swansea University, Wales

Sena has just completed her MSc in Clinical Psychology in the United Kingdom. During her undergraduate years in psychology, she took part in various research projects and, in addition, gained a lot of writing experience. She continues to develop herself in many ways in writing and psychology.

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