A fever is a temporary increase in your body temperature, often due to an illness. As a general rule, a temperature of over 37.5°C (99.5°F) in children or adults is classed as a fever. 


It is usually a sign that your body is trying to fight an illness or infection. For an adult, a fever may be uncomfortable, but usually isn’t a cause for concern unless it reaches 39.4 C or higher. For infants and toddlers, an elevated temperature may indicate a serious infection that requires immediate medical attention.


If you or someone in your family suddenly gets a high fever with severe chills or loss of consciousness, you should contact emergency and wait for an ambulance.


Fever occurs when a part of the brain called the hypothalamus shifts the set point of your normal body temperature upward. When this happens, you may feel chilled and add layers of clothing, or you may start shivering to generate more body heat. This eventually results in a higher body temperature.


Having a fever is a sign that something out of the ordinary is going on in your body – often the immune system working at high speed to fight off infection. Most bacteria and viruses do well when your body is at your normal temperature, so you get a fever because your body is trying to kill the virus or bacteria that caused the infection.


There are numerous different conditions that can trigger a fever. Some possible causes include:


  • infections, including the flu and pneumonia
  • some immunizations, such as diphtheria or tetanus (in children)
  • teething (in infants)
  • some inflammatory diseases, including rheumatoid arthritis and Crohn’s disease
  • blood clots
  • extreme sunburn
  • food poisoning
  • some medications, including antibiotics


Fever is a common symptom of many medical conditions:


  • Infectious disease, e.g., COVID-19, Ebola, gastroenteritis, HIV, influenza, Lyme disease, Borreliosis, malaria, mononucleosis, as well as infections of the skin, e.g., abscesses and boils.
  • Immunological diseases, e.g., relapsing polychondritis, autoimmune hepatitis, granulomatosis with polyangiitis, Horton disease, inflammatory bowel diseases, Kawasaki disease, lupus erythematosus, sarcoidosis, and Still’s disease;
  • Tissue destruction, as a result of cerebral bleeding, crush syndrome, hemolysis, infarction, rhabdomyolysis, surgery, etc.
  • Cancers, most commonly kidney cancer, leukemia, and lymphomas;
  • Metabolic disorders, e.g., gout, and porphyria;


Adult and pediatric manifestations for the same disease may differ.


But not all fevers are due to illness. Other factors, such as your menstrual cycle, pregnancy, intense exercise, time of day and weather, can also affect body temperature.


Recognizing a fever can enable you to get treatment and proper monitoring for it. You can measure the temp in the armpit, mouth, rectum, ear or forehead. Normal body temperature is typically around 37°C (98.6°F). However, the normal body temperature for each person can vary slightly. 


In health care, the interval 37.6-37.9 degrees is called elevated body temperature – if the temperature exceeds 38 degrees, it is counted as fever. Hyperthermia in an adult usually counts from 39-40 degrees and when the fever exceeds 41 degrees the temperature increase in itself can be harmful.


Depending on the cause of the fever, additional symptoms may include:


  • sweating
  • shivering
  • headache
  • muscle aches
  • loss of appetite
  • dehydration
  • general weakness

Prevention and protection

Limiting exposure to infection is one of the best ways to prevent a fever. Here are some tips that can help reduce your exposure:


  • Wash your hands often, especially before eating, after using the toilet, and after being around large numbers of people.
  • Show your children how to wash their hands properly. Instruct them to cover both the front and back of each hand with soap and rinse thoroughly under warm water.
  • Avoid touching your nose, mouth, or eyes. Doing so makes it easier for viruses and bacteria to enter your body and cause infection.
  • Cover your mouth when you cough and your nose when you sneeze. Teach your children to do the same.
  • Avoid sharing cups, glasses, and eating utensils with other people.


Try to rest when you have a fever so that your body has the opportunity to recover. Avoid sports and exercise because it impairs the immune system’s ability to fight the infection and increases the risk of complications, such as heart muscle inflammation and joint problems.


It is important to:


  • Drink properly – to replace the fluid you lose
  • Rest – allow the body to recover before going to school or work
  • Abstain from exercise – physical exertion in the case of fever can be directly harmful.


There is no universal treatment for a fever – fever is a natural reaction when the body fights viruses and bacteria and it usually goes away by itself after a few days. A number of over-the-counter medications lower a fever, but sometimes a fever is better left untreated as it seems to play a key role in helping your body fight off a number of infections.


Medications that lower fevers are called antipyretics. The antipyretic ibuprofen is effective in reducing fevers in children. It is more effective than acetaminophen (paracetamol) in children. Ibuprofen and acetaminophen may be safely used together in children with fevers.


The treatment depends entirely on what causes the fever. 


Important to know about Reye’s syndrome

Children and adolescents under 18 years of age should not take aspirin (acetylsalicylic acid medication) without a doctor’s recommendation due to the risk of Reye’s syndrome. An uncommon but serious condition, it can affect the brain and liver with symptoms such as cramps, abdominal pain, vomiting and loss of consciousness. Sometimes Reye’s syndrome can have a fatal outcome.

When to consult a doctor



Call your doctor if your temperature is 39.4 C or higher. Seek immediate medical attention if any of these signs or symptoms accompanies a fever:


  • Severe headache
  • Unusual skin rash, especially if the rash rapidly worsens
  • Unusual sensitivity to bright light
  • Stiff neck and pain when you bend your head forward
  • Mental confusion
  • Persistent vomiting
  • Difficulty breathing or chest pain
  • Abdominal pain or pain when urinating
  • Convulsions or seizures



An unexplained fever is a greater cause for concern in infants and in children than in adults. Seek medical attention if your child suffers from a fever and is:


  • Younger than age 3 months and has a rectal temperature of 38C or higher.
  • Between ages 3 and 6 months and has a rectal temperature up to 38.9 C and seems unusually irritable, lethargic or uncomfortable or has a temperature higher than 38.9 C.
  • Between ages 6 and 24 months and has a rectal temperature higher than 38.9 C that lasts longer than one day but shows no other symptoms. If your child also has other signs and symptoms, such as a cold, cough or diarrhea, you might call your child’s doctor sooner based on severity.
  • Is listless or irritable, vomits repeatedly, has a severe headache or stomach ache, or has any other symptoms causing significant discomfort.
  • Has a fever after being left in a hot car. Seek medical care immediately.
  • Has a fever that lasts longer than three days.
  • Appears listless and has poor eye contact with you.


Ask your child’s doctor for guidance in special circumstances, such as a child with immune system problems or with a pre-existing illness.

How APPOTEK can help

APPOTEK can help you with fever. A nurse or doctor will make an individual assessment based on your symptoms. You may then be prescribed treatment or referred for further examination. 


For a fever without a clear explanation, a physical examination is often required. If your child is affected, they should also attend the consultation.


Vadym Diadiun, Doctor of Medicine, M.D.