Last updated: Aug 5, 2026Published on: Jul 31, 2026
Table of Contents
Introduction
Fever is one of the most common signs that your body is responding to an infection or another health condition1. Although a rise in body temperature can feel worrying, it is often a normal part of your body’s defence system and usually improves with appropriate care. In some cases, however, fever can be a sign of an illness that needs medical attention1,2. In this blog, we explain what fever is the main types of fever, common symptoms, stages of fever, safe management tips, and when to consult a doctor.
What Is a Fever?
A fever is a temporary increase in body temperature. It happens when the body’s temperature-control centre in the brain, called the hypothalamus, raises the body’s “set point” in response to infection, inflammation, or other triggers2.
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Normal body temperature is generally around 36.5°C to 37.5°C (97.7°F to 99.5°F), although it can vary slightly between individuals and throughout the day2.
In adults, a body temperature of 38°C (100.4°F) or higher is generally considered a fever. The exact reading can vary depending on where and how the temperature is measured, such as by mouth, ear, forehead, armpit, or rectum2.
Note: Fever itself is not a disease. It is a sign that tells you the immune system is responding to an underlying problem, most often an infection.
What Are the Types of Fever?
You may have wondered how many types of fever actually exist.
Fever can be classified in several ways. Doctors commonly classify fever based on body temperature, how long it lasts, the pattern of temperature changes, and its underlying cause.
Understanding the different types of fever can help you describe your symptoms more clearly to a doctor and may guide the next steps in care. Let us look at the main ways fever is classified:
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1. Types of fever based on body temperature
The severity of fever depends on how much the body temperature rises above the usual range2.
Type
Body Temperature
Description
Low-grade fever
37.3°C to 38.0°C (99.1°F to 100.4°F)
A mild increase in temperature. It may occur with viral infections, mild bacterial infections, after vaccination, or with inflammatory conditions. It usually does not require specific treatment unless you feel very uncomfortable or symptoms worsen.
Moderate fever
38.1°C to 39.0°C (100.6°F to 102.2°F)
Common in infections such as influenza, COVID-19, urinary tract infections, and pneumonia. Most people experience chills, fatigue, headache, and body aches at this stage.
High-grade fever
39.1°C to 41°C (102.4°F to 105.8°F)
May indicate a more serious infection or inflammatory condition. Medical attention is recommended if the fever persists or occurs with confusion, difficulty breathing, severe pain, dehydration, or worsening symptoms.
Hyperpyrexia
Above 41°C (105.8°F)
A medical emergency that needs immediate care. Hyperpyrexia can occur with severe infections, heat stroke, certain nervous system conditions, or serious drug reactions. If not treated promptly, it may lead to organ damage.
2. Types of fever based on duration
The length of time a fever lasts can provide clues about its cause3.
Acute Fever
Lasts less than 7 days.
Most commonly caused by viral infections like the common cold.
Usually improves once the underlying illness gets better.
Subacute Fever
Persists for 7 to 14 days.
May occur with infections such as typhoid fever.
Further medical evaluation may be needed if the cause is not obvious.
Chronic or Persistent Fever
Lasts more than 14 days.
Possible causes include tuberculosis, HIV, some cancers, autoimmune conditions, and other long-term infections or inflammatory illnesses.
Requires thorough medical investigation to determine the underlying cause.
3. Types of fever based on temperature pattern
The way body temperature changes throughout the day often provides important diagnostic clues.
Continuous (Sustained) Fever: In continuous fever, body temperature stays high throughout the day and changes by less than 1°C (1.8°F) over 24 hours. The temperature does not return to normal during this period. Common causes include3:
Remittent Fever: In remittent fever, the temperature stays above normal but rises and falls by more than 1°C during the day. It does not return to normal between these changes. Common causes include3:
Infective endocarditis
Certain bacterial infections, such as brucellosis and rickettsial infections
Intermittent Fever: In intermittent fever, the temperature rises for several hours, returns to normal, and then rises again later. Common causes include3:
Depending on the timing, intermittent fever may be described as:
Quotidian: Fever occurs every day.
Tertian: Fever occurs every alternate day, or about every 48 hours.
Quartan: Fever occurs every third day, or about every 72 hours.
Relapsing Fever: Relapsing fever is characterised by episodes of fever lasting several days, followed by fever-free periods before the fever returns3. Common causes include:
Tick-borne or louse-borne relapsing fever (Borrelia infection)
Certain forms of Malaria
4. Types of fever based on underlying cause
Fever can be classified based on what is causing it:
Infectious Fever: This is the most common type of fever. It is caused by microorganisms, or germs, such as viruses, bacteria, fungi, or parasites. Examples include3:
Inflammatory or Autoimmune Fever: This occurs when inflammation activates the immune system even when there is no infection. Autoimmune conditions are illnesses in which the immune system mistakenly attacks the body’s own tissues. Examples include4:
Rheumatoid arthritis
Systemic lupus erythematosus (SLE)
Vasculitis
Adult-onset Still’s disease
Drug-Induced Fever: Some medications can trigger fever as an adverse reaction, even without an infection. Common medications include5:
Certain antibiotics
Anticonvulsants
Allopurinol
Heparin
Some chemotherapy and immunotherapy drugs
Neoplastic (Cancer-Related) Fever: Certain cancers can cause persistent fever through inflammation or immune system activation. Examples include6:
Lymphoma
Leukaemia
Renal cell carcinoma
Other advanced cancers
Heat-Related Fever (Hyperthermia): Hyperthermia is different from true fever. In fever, the brain raises the body’s temperature set point. In hyperthermia, the body overheats because it cannot lose enough heat. Examples include2,7:
Heat stroke
Heat exhaustion
Excessive environmental heat exposure
Fever of Unknown Origin: Fever of unknown origin refers to a persistent fever, usually 38.3°C (101°F) or higher on multiple occasions, that remains unexplained after appropriate medical evaluation. Common causes include8:
Undiagnosed infections
Autoimmune diseases
Cancers (malignancies)
Rare inflammatory disorders
Common Symptoms of Fever
Fever symptoms can vary depending on the cause, how high the temperature is, and a person’s age. While a raised body temperature is the main sign of fever, other symptoms may indicate that the body is fighting an infection or illness. These include9,10:
Fever often progresses through three stages as the body raises, maintains, and then lowers its temperature in response to an infection or another trigger. These include2,11:
Chill stage (onset stage): The hypothalamus raises the body’s temperature set point. To reach this higher temperature, the body produces and conserves heat. This is why you may feel cold, shiver, or want to cover yourself even though your temperature is rising.
Plateau stage (hot stage): The body reaches the new temperature set point and keeps the temperature elevated while the immune system responds to the underlying cause. During this stage, you may feel hot, tired, or achy.
Defervescence (recovery or sweating stage): As the illness improves or treatment begins to work, the hypothalamus lowers the temperature set point. The body then releases extra heat, often through sweating. This is sometimes called the recovery stage.
Diagnosis of Different Types of Fever
Diagnosing a fever means measuring body temperature and finding the underlying cause. Depending on your symptoms and medical history, your doctor may recommend one or more of the following tests or checks2,8:
Medical history: Your doctor may ask how long the fever has lasted, whether it comes and goes, and whether you have symptoms such as cough, pain, rash, travel history, exposure to infections, recent medicines, or existing health conditions.
Physical examination: To look for signs of infection or inflammation by checking vital signs, throat, ears, lungs, skin, abdomen, and lymph nodes.
Blood tests: Tests such as a complete blood count, blood culture, C-reactive protein, erythrocyte sedimentation rate, procalcitonin, and liver and kidney function tests may help detect infection, inflammation, or organ involvement.
Urine, stool, or respiratory tests: These may include urinalysis, urine culture, stool examination or culture, throat swab, and sputum culture to look for infections in specific parts of the body.
Disease-specific tests: Such as malaria tests, dengue NS1 antigen or antibody tests, typhoid blood culture, COVID-19 and influenza tests, tuberculosis tests, and other region-specific infectious disease tests when clinically indicated.
Imaging studies: Including chest X-ray, CT scan, or MRI to identify infections or inflammation affecting internal organs.
Special investigations: For persistent, recurrent, or unexplained fever, tests such as autoimmune markers, HIV testing, bone marrow examination, biopsy, or PET-CT scan may be considered.
Tips for Managing Fever Correctly
Most fevers caused by mild viral infections improve with supportive care. These steps can help reduce discomfort and support recovery10,12:
Drink ample water, juice, soups, or other fluids to replace fluids lost through sweating.
Rest and allow your body to conserve energy and support the immune system in fighting the underlying illness.
Medicines such as paracetamol (acetaminophen) or ibuprofen may help reduce fever and relieve discomfort. Always follow the recommended dose, avoid taking more than advised, and check with a doctor if you are unsure.
Dress in loose, breathable clothing and avoid excessive layering to help the body regulate its temperature.
Maintain a comfortable room temperature and avoid overheating. A fan may help if tolerated.
If needed, gently sponge exposed skin with lukewarm (tepid) water. Sitting near a fan may help the water evaporate more quickly and provide a cooling effect.
Check your temperature from time to time and seek medical attention if the fever is high, persistent, or associated with warning symptoms.
Precautions for Fever
Taking the right precautions can help prevent complications and ensure timely medical care. Below are some steps that you can take10,12:
Consult a doctor if the fever lasts longer than 3 days, repeatedly returns, or continues despite treatment.
Avoid alcohol and limit drinks such as tea and coffee, as they may contribute to dehydration.
Avoid cold baths. Very cold water can narrow blood vessels in the skin and trigger shivering, which may increase body temprature instead of lowering it.
Infants, older adults, pregnant women, and people with weakened immune systems should seek medical advice early if they develop a fever.
Seek immediate medical attention if fever is associated with confusion, difficulty breathing, severe abdominal pain, persistent vomiting, seizures, stiff neck, or a rash that spreads rapidly.
Do not take antibiotics unless they are prescribed by a doctor. Antibiotics do not treat viral infections and should only be used when needed.
Do not give aspirin to children or teenagers with a fever unless specifically advised by a doctor because of the risk of Reye’s syndrome.
If your doctor prescribes medicines, take them exactly as directed. If an antibiotic is prescribed, complete the full course unless your doctor advises otherwise.
Most fevers improve within a few days with rest and supportive care. However, you should consult a doctor if you or your child10,12:
Have a fever lasting more than 3 days or one that keeps recurring.
Seek immediate medical attention if a child has a seizure associated with fever (febrile seizure), especially if it is the first episode, lasts longer than 5 minutes, or the child does not recover promptly afterward.
Have a temperature of 40°C (104°F) or higher.
Continue to feel unwell despite home management.
Have recently travelled abroad, undergone surgery, or had a medical procedure.
Have a weakened immune system, are receiving cancer treatment, or are taking immunosuppressive medicines.
Develop warning symptoms such as difficulty breathing, severe headache, stiff neck, persistent vomiting, severe abdominal pain, confusion, excessive drowsiness, seizures, muscle spasms, or a rash that does not fade when pressed.
Have any other symptoms that concern you or seem to be getting worse.
Conclusion
A fever is often a sign that your immune system is doing its job, but it is important to know when it needs closer attention. Understanding the different types of fever, their symptoms, and the warning signs can help you manage a fever safely and recognise when medical care is needed. Most fevers improve with simple supportive measures, but persistent, recurrent, or severe fever should not be ignored. If you are unsure about the cause or your symptoms get worse, consult a doctor for timely evaluation and care.
Most fevers caused by viral infections improve within about 3 days, although some may last up to a week. If a fever lasts for more than 3 days, keeps coming back, or occurs with severe symptoms, consult a doctor2,12.
Is fever contagious?
No, fever itself is not contagious. However, the underlying illness causing the fever, such as influenza or other viral or bacterial infections, may spread from person to person3.
Is fever a sign of pregnancy?
Fever is not a sign of pregnancy. It usually suggests an infection or another medical condition. Pregnant individuals who develop a fever should seek medical advice promptly, as some infections can affect both the mother and the developing baby12.
Is fever a symptom of cancer?
Yes, in some cases, certain cancers, particularly lymphoma and leukaemia, may cause persistent or recurrent fever. However, infections are a much more common cause of fever than cancer2,6.
Can teething cause fever?
Teething may cause a slight rise in body temperature, but it does not usually cause a true fever of 38°C (100.4°F) or higher. A high fever during teething is more likely due to another illness and should be checked by a doctor1,2,13.
Can dehydration cause fever?
Severe dehydration can contribute to a rise in body temperature, especially during hot weather14. However, dehydration is more often a result of fever than the main cause, because fever increases fluid loss through sweating10.
Can fever delay periods?
A fever itself does not usually delay your period. The underlying illness, along with physical stress, inflammation, and the immune response it triggers, may temporarily affect hormone levels and delay ovulation15,16. This can lead to a late or irregular menstrual period. In most cases, the menstrual cycle returns to normal once you recover.
References
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Savioli G, Zanza C, Longhitano Y, et al. Heat-Related Illness in Emergency and Critical Care: Recommendations for Recognition and Management with Medico-Legal Considerations. Biomedicines. 2022;10(10):2542. doi:10.3390/biomedicines10102542. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC9599879/
Ye Y, Xin X, Du X, Bai Y, Shen H. Fever duration, peak temperature and associated symptoms in Chinese adults with SARS-CoV-2 infection: a cross-sectional study. Front Med. 12:1665460. doi:10.3389/fmed.2025.1665460. Available from: https://pubmed.ncbi.nlm.nih.gov/41281992/
Kiekkas P, Brokalaki H, Manolis E, Askotiri P, Karga M, Baltopoulos GI. Fever and standard monitoring parameters of ICU patients: A descriptive study. Intensive Crit Care Nurs. 2007;23(5):281-288. doi:10.1016/j.iccn.2007.04.001. Available from: https://pubmed.ncbi.nlm.nih.gov/17531490/
Evans SS, Repasky EA, Fisher DT. Fever and the thermal regulation of immunity: the immune system feels the heat. Nat Rev Immunol. 2015;15(6):335-349. doi:10.1038/nri3843. Available from: https://pubmed.ncbi.nlm.nih.gov/25976513/
Vigil P, Meléndez J, Soto H, Petkovic G, Bernal YA, Molina S. Chronic Stress and Ovulatory Dysfunction: Implications in Times of COVID-19. Front Glob Womens Health. 2022;3:866104. doi:10.3389/fgwh.2022.866104. Available from: https://pubmed.ncbi.nlm.nih.gov/35677754/
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