When you wake up one morning, your child's forehead is burning, you find yourself shivering when you come home from work in the evening, or you suddenly start feeling cold in the middle of the night... A symptom that we all encounter many times in our lives: fever. So why does the fever rise? This seemingly simple question actually opens the door to one of the most complex and intelligent defense mechanisms of our body. Fever is not a disease, but rather a powerful weapon that the body uses to fight disease. In this article, I will explain in detail all the scientific details of the question "why does the fever rise?", the 15 most common reasons, in which situation you should really worry, and what you should (or should not) do at home.
What is Fire and How Does It Form in Our Body?
Our body temperature is normally kept in a very narrow range between 36.5-37.2 °C. This control is provided by a small but very powerful center in the brain called the hypothalamus. The hypothalamus is literally the body's thermostat. When it detects infection, inflammation, or other danger, our immune system secretes substances such as interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha). These substances are called "pyrogen" (fire-producing). Pyrogens mix with the blood, reach the hypothalamus and raise the thermostat setting. For example, the body, which is normally in balance at 36.8 °C, suddenly receives an order saying "the new target is 39 °C."
When this target changes, the body perceives its current temperature as low and immediately starts working to produce heat. Your muscles contract and relax rapidly, and you begin to tremble. The blood vessels in the skin constrict, your skin becomes pale and you feel cold. This phase is called the "chilling phase". When body temperature reaches the target, shivering stops and the plateau phase begins. You now have fever. Then, when the danger is over, the hypothalamus lowers the thermostat again, this time the heat is released through sweating and dilated vessels, and the fever decreases.
The most important benefit of fever is that it puts the immune system into turbo mode. Fever between 38-39 °C slows down the proliferation of many viruses and bacteria, accelerates the movement of white blood cells, increases the production of interferon and enables the liver to hold iron, making it difficult for microbes to multiply. In short, fire is the body's "battle mode".
Why Does Fever Rise? 15 Most Common Reasons
1. Viral Infections
Flu, cold, COVID-19, RSV, enterovirus, measles, rubella, chickenpox, hand-foot-mouth disease, fifth disease, sixth disease... The most common cause of fever is viruses. Fever begins within 1-3 days after viruses enter the body and usually stays between 38-40 °C. Viral fever usually subsides spontaneously within 3-5 days.
2. Bacterial Infections
Throat inflammation (beta microbe), middle ear infection, pneumonia, urinary tract infection, meningitis, appendicitis, bone inflammation... In bacterial infections, the fever is usually higher and starts suddenly. If there is a fever of 39-40 °C and above, bacterial infection should definitely be considered.
3. Teething
Mild fever (37.5-38.5 °C) is common in babies during the teething period between 6-24 months. However, a fever above 38.5 °C should not be attributed to teething; another infection should be investigated.
4. Fever After Vaccination
Fever is very normal in the first 48 hours after the combination vaccine (DTB-IPV-Hib), KPA (pneumonia), MMR (measles-rubella-mumps), and chickenpox vaccine. This fever is proof that the body's immune system is working.
5. Autoimmune and Rheumatic Diseases
In diseases such as juvenile rheumatoid arthritis, systemic lupus erythematosus (SLE), Kawasaki disease, Still's disease, fever can last for weeks and is difficult to reduce with medication.
6. Drug Fever
Antibiotics (especially the beta-lactam group), epilepsy medications, allopurinol, and some blood pressure medications can cause fever. Drug fever usually occurs 7-10 days after starting the drug and goes away in 48-72 hours when the drug is stopped.
7. Cancers
Lymphoma, leukemia, liver-kidney tumors, bone metastases can cause long-term, unexplained fever. If night sweats and weight loss accompany, oncology evaluation is required.
8. Heat Stroke
After staying in the heat for a long time in the summer or after excessive exercise, the body cannot release its own heat and the fever rises above 40 °C. Confusion, vomiting, and convulsions may occur. It is an emergency.
9. Thyroid Diseases (Hyperthyroidism)
In cases such as Basedov-Graves disease and thyroid gland inflammation, metabolism accelerates and a constant mild fever (37-38 °C) may occur.
10. Hidden Abscesses
If there is a hidden abscess in the abdomen, at the root of the tooth, around the kidney or in the lung, the fever will fluctuate for a long time and may not decrease with antibiotics.
11. Traveler Fever and Tropical Diseases
Diseases such as malaria, typhoid, dengue fever, brucellosis, leptospirosis manifest themselves with high fever after traveling abroad.
12. Familial Mediterranean Fever (FMF)
A genetic disease seen in one in every 200-1000 people in Turkey. Very high fever attacks lasting 1-3 days and abdominal, head and chest pain occur. It is completely controlled with colchicine treatment.
13. Brain and Nervous System Diseases
Brain hemorrhage, meningitis, encephalitis, hypothalamus tumors may disrupt the thermostat and cause fever.
14. Stress and Psychogenic Fever
Although it is very rare, fever may rise between 37-38 °C in cases of intense stress, panic attacks and somatoform disorders. All tests are normal.
15. Blood Diseases and Hemolytic Crises
Destruction of blood cells causes fever in attacks of sickle cell anemia, thalassemia, and G6PD deficiency.
How Dangerous Is Fire?
Axillary fever of 38 °C and above is an emergency in babies between 0-3 months. Since the immune system is very weak in this age group, serious infections such as meningitis and sepsis can progress rapidly. A fever over 38.5 °C is considered serious in children between 3 months and 3 years of age, and a fever over 40 °C in adults and over 3 years of age is considered serious. A fever of 41 °C and above poses a risk of brain damage and one should definitely go to the hospital.
What Reduces Fever and What Does Not? Things to Do at Home
Fever itself is not harmful, the underlying disease is harmful. Therefore, it is more important to make the child/adult comfortable than to reduce the fever. Paracetamol (15 mg/kg/dose, every 4-6 hours) and ibuprofen (10 mg/kg/dose, every 6-8 hours) are the safest antipyretics. They can be used alternatively. A warm shower (with water 2-3 °C lower than body temperature), plenty of fluid intake, thin clothing, and a room temperature of 21-22 °C are very effective. Old methods such as cold showers, alcohol swabs, and applying vinegar-cologne should never be used. Aspirin should never be given to children (risk of Reye's syndrome). Linden, sage, and ginger-infused monk fruit tea may be supportive, but it is not a substitute for medicine.
Frequently Asked Questions
1. Why does the fever rise but we feel cold?
When the body raises the target temperature via the hypothalamus, the current body temperature is suddenly considered “low”. That's why the skin vessels constrict, blood is drawn to the internal organs, the skin cools and you feel cold. At the same time, the muscles try to produce heat by shaking. This is a physiological deception. In fact, it is very normal to feel cold while your fever rises.
2. Fever in children exceeds 40 degrees, what should I do?
First of all, stay calm. Undress the child, take a warm shower, or put a warm cloth on his arms and legs. Give paracetamol or ibuprofen (do not overdose). Fever decreases by 1-1.5 °C in 10-15 minutes. If it is less than 3 months old, has seizures, confusion, cyanosis, constant vomiting, difficulty breathing, call 112 or go to the nearest hospital without waiting.
3. If I don't give an antipyretic, will the fever damage the brain?
No. Fever up to 42 °C does not cause brain damage in children and adults with normal immune systems. Brain damage is only seen in cases such as heat stroke and encephalitis. We give antipyretics to make the child comfortable, not to prevent the fever from damaging the brain.
4. Why does fever rise more at night?
Due to the body's biological clock (circadian rhythm), the cortisol hormone is high in the morning and low in the evening and night. Cortisol has an antipyretic effect. Therefore, in the same infection, the fever, which is 38 °C in the morning, may rise to 39-39.5 °C in the evening. This is completely normal.
5. Is it true, “There is a fever, let's take antibiotics immediately”?
Absolutely wrong. 85-90% of fever is due to viruses and antibiotics do not affect viruses. Unnecessary use of antibiotics causes the formation of resistant bacteria and diarrhea. Antibiotics should only be started after a doctor's examination and, if necessary, a blood test.
Fever is one of our body's oldest and most effective defense mechanisms. It is best to see it as a friend, not an enemy, and focus on finding the underlying cause. If you or your child has a long-lasting, recurring or very high fever, be sure to consult your doctor. Stay healthy.
