Fever (High Temperature): Causes, Stages, Treatments, and Red Flags

Introduction

Fever (also known as a high temperature) is one of the most common signs that the body is fighting an infection or another health condition¹.

While most fevers resolve with appropriate care, some may indicate a more serious underlying problem that requires medical attention¹. Therefore, understanding the causes, stages, treatment options, and warning signs of fever can help individuals manage symptoms appropriately and seek timely medical care when needed. 

This blog explains what fever is, its common causes, the different stages of fever, available treatment approaches, and the red flags that should not be ignored. 

What Is a Fever?

A fever is a temporary rise in body temperature that occurs when the immune system responds to an infection, inflammation, or another health condition. It is important to understand that fever is not a disease itself but a sign that the body is actively working to protect and heal itself. 

So, what actually happens inside the body? When germs such as viruses or bacteria enter the body, the immune system releases substances that help fight the infection. As part of this natural defence response, the body’s temperature is increased, creating an environment that can make it harder for some germs to survive and multiply¹.

Interesting Fact: The hypothalamus is a small region in the brain that acts as the body’s thermostat. This regulates the increase in temperature during a fever¹.

What Body Temperature Is Considered a Fever?

Body temperature can vary slightly from person to person and may fluctuate throughout the day. In general, a temperature above the normal range is considered a fever^1,2. 

Important points to remember: 

• Children, especially infants and young children, may develop higher temperatures than adults in response to common infections³. However, the severity of illness may not always correlate with how high the temperature rises. 
• In both cases, persistent fever or fever accompanied by concerning symptoms may need medical evaluation, even if the temperature is not extremely high. 

How To Check Fever Accurately

Measuring body temperature with a thermometer is the most reliable way to confirm whether a person has a fever. There are two ways to check for a fever^4,5.

• Using a Digital Thermometer: A digital thermometer can be used to measure temperature in the mouth (oral), armpit (axillary), or rectum (rectal), depending on the person’s age and the manufacturer’s instructions. 
• Using a Manual (Glass) Thermometer: Some people may still use traditional glass thermometers. If using one, handle it carefully and follow the manufacturer’s instructions. 

Steps to record temperature: 

• Ensure the thermometer is clean and the reading is reset according to the instructions. 
• Place the thermometer in the recommended site to record temperature. 
• Leave it in place for the recommended amount of time/until reading complete signal is observed. 
• Remove the thermometer and read the temperature carefully^4,6.
• A body temperature above 37.2°C (99°F) is generally considered a fever. Refer to the section above for the classification of fever based on temperature ranges. Normal temperature ranges can vary depending on the site of measurement, time of day, age, and individual factors. 
• Digital thermometers display the temperature reading directly on the screen. 
• Glass thermometers require the user to read the temperature scale manually. Hold the thermometer at eye level and locate the end of the fluid column. Read the temperature by matching it to the scale markings. The long lines represent whole degrees, while the shorter lines between them represent smaller increments of temperature. For example⁶:
• On the Fahrenheit scale, if there are four short lines between 99°F and 100°F, each short line represents 0.2°F. If the fluid ends at the third short line after 99°F, the temperature is 99.6°F.  

Note: Mercury-containing glass thermometers are generally not recommended because they can break and release mercury, which is toxic. Electronic (digital) thermometers are preferred as they are safer, easier to use, and provide quick and accurate temperature readings⁴.

Symptoms of Fever

The symptoms of fever can vary depending on the underlying cause, the severity of the illness, and the person’s age. While an elevated body temperature is the hallmark sign, fever is often accompanied by a range of other symptoms as the body works to fight infection. Some common fever symptoms include^1,7,8:

• Nausea  
• Vomiting  
• General feeling of being unwell  
• Chills or shivering 
• Sweating  
• Muscle aches and body pains 
• Fatigue or weakness 
• Light-headedness  
• Increased thirst or dehydration 
• Difficulty concentrating or feeling mentally foggy 
• Rapid heartbeat 
• Rapid breathing 

If an infant has a fever, you may observe fever symptoms like^7,9: 

• Fussiness or irritability 
• Excessive crying 
• Poor feeding or reduced appetite 
• Sleepiness or difficulty waking up 
• Reduced activity or playfulness 
• Flushed skin 
• Febrile seizures (uncommon) 

Causes of Fever

Fever can occur for many reasons, but it most commonly occurs as a response to some kind of infection. However, it may also result from other underlying medical conditions. Some of the common causes of fever include: 

1. Viral infections 

• Common cold 
• Influenza (flu) 
• COVID-19 
• Dengue fever 
• Viral gastroenteritis 
• Chickenpox and other viral illnesses^7,8

2. Bacterial infections 

• Pneumonia 
• Kidney or urinary tract infections 
• Ear or throat infections 
• Tuberculosis 
• Tonsilitis  
• Meningitis^1,8,9

3. Parasitic infections 

• Malaria 
• Amoebiasis 
• Toxoplasmosis 
• Other parasitic diseases common in certain regions¹⁰ 

4. Drug-induced fever 

• Reactions to certain antibiotics 
• Anti-seizure medications 
• Some blood pressure medications¹¹ 

5. Post-vaccination fever 

• Fever following routine childhood vaccinations¹¹
• Fever after influenza, COVID-19, or other vaccines 

6. Other causes

• Autoimmune diseases, such as rheumatoid arthritis¹² 
• Heat-related illness or heatstroke¹¹
• Certain cancers, such as lymphoma or leukaemia⁸

Note: A fever that continues or comes back and for which no clear cause can be identified despite proper medical evaluation is known as a fever of unknown origin¹³.

Types of Fever and What They Mean

Fevers can be classified based on how long they last and how they occur. The duration and pattern of a fever can sometimes provide clues about its underlying cause.  

Based on duration, the types include¹⁴:

• Acute Fever: Lasts for less than 7 days and is commonly associated with viral infections, upper respiratory tract infections, malaria, and other short-term illnesses. 
• Subacute Fever: Lasts between 7 and 14 days and may occur in conditions such as typhoid fever and certain bacterial infections. 
• Chronic (Persistent) Fever: Lasts for more than 14 days and may be caused by tuberculosis, HIV infection, cancers, or autoimmune diseases. 

Based on pattern, the types include¹¹:

• Continuous Fever: Fever remains consistently elevated with minimal daily fluctuation, often less than about 1°C. Commonly associated with typhoid or bacterial infections. 
• Intermittent and Remittent Fever: 
  • Intermittent fever is when the temperature fluctuates daily and drops back to normal before rising again. This pattern is common in malaria, tuberculosis, pyogenic infections or Hodgkin’s lymphoma.  
  • Remittent fever is when the temperature fluctuates throughout the day but never falls back to normal. These are often associated with infectious diseases such as infective endocarditis and some other atypical bacterial infections. 
• Recurring/Relapsing Fever: Fever that goes away for days or weeks and then returns after a period of normal temperature, usually associated with unresolved infections, inflammatory or autoimmune conditions or some cancers. 

Note: Any cause of acute fever can become persistent or chronic if it is not properly diagnosed and treated under medical guidance. 

The Stages of a Fever

Most fevers follow a predictable pattern, progressing through different stages as the body’s immune system fights an infection. The stages are as follows: 

1. Rising Stage 

The rising stage begins when the immune system detects an infection or another trigger and signals the body to raise its temperature. During this phase, the hypothalamus increases the body’s temperature set point, causing blood vessels in the skin to constrict and reducing heat loss. As a result, a person may experience chills or shivering¹⁵.

Practical tip: Wear light layers of clothing and stay hydrated, but avoid excessive layering of too many clothes, which may increase discomfort⁷.

2. Peak Stage 

During the peak stage, the body reaches and maintains its elevated temperature while actively fighting the underlying illness. The immune system remains highly active, and symptoms such as feeling hot, fatigue, and muscle aches are common¹. 

Practical tip: Rest as much as possible and drink plenty of fluids to avoid dehydration⁸.

3. Recovery Stage 

The recovery stage begins when the underlying illness starts to improve, and the body’s temperature begins to return to normal. The hypothalamus lowers the temperature set point, and blood vessels in the skin dilate to release excess heat. This often leads to sweating as the body cools down^1,15.

Practical tip: Continue drinking fluids and avoid strenuous activity until you feel fully recovered⁷.

Diagnosis of Fever

Diagnostic tests may be needed when a fever is high, persists for several days, recurs frequently, is accompanied by concerning symptoms, or when the underlying cause is unclear. Based on your symptoms, your doctor may order: 

• Complete Blood Count (CBC): Evaluates white blood cells, red blood cells, and platelets to help identify infections, inflammation, or blood disorders¹⁶.
• C-Reactive Protein (CRP): Measures the level of inflammation in the body and helps assess the severity of an infection or inflammatory condition¹⁷.
• Erythrocyte Sedimentation Rate (ESR): Detects inflammation and may help identify chronic infections or autoimmune diseases¹⁷.
• Other tests: Depending on your symptoms and medical history, your doctor may recommend tests such as urine analysis, chest X-ray, malaria testing, dengue testing, typhoid testing, or other investigations to identify the cause of the fever. 

Note: The primary goal of fever diagnosis is to identify and manage the underlying cause of the fever. This helps the doctor to guide the treatment. 

Treatment of Fever

Fever is typically managed depending on its underlying cause. While fever-reducing medications can help relieve discomfort, addressing the condition responsible for the fever is equally important. Here are some common fever treatment/management options: 

• Antipyretics (Fever-Reducing Medications): Medications such as paracetamol (acetaminophen), aspirin or ibuprofen may be used to reduce fever and improve comfort¹. Remember that aspirin is completely restricted for use in children due to risk of serious side effects. 
• Antibiotics: Antibiotics are effective only for bacterial infections and should be used only when prescribed by a doctor¹³. They do not work against viral infections. 
• Antiviral Medications: Certain viral infections, such as influenza, may require antiviral medications, particularly in high-risk individuals¹⁸.
• Antimalarial Medications: Fevers caused by malaria require specific antimalarial drugs to eliminate the parasite and avoid complications¹⁹.
• Intravenous (IV) Fluids: IV fluids may be needed in cases of severe dehydration, persistent vomiting, or serious illness when adequate fluid intake by mouth is not possible²⁰.

If a fever continues or returns after receiving the proper therapy for a detected infection, an underlying non-infectious cause, such as an autoimmune or inflammatory disorder, cancer, or other illnesses, may be indicated. For treatment in these situations, a thorough clinical assessment and additional diagnostic testing may be necessary to identify the underlying reason first. 

Note: Avoid self-medicating, especially with antibiotics or other prescription medications. You should always consult a doctor for the appropriate fever treatment. 

How to Reduce Fever at Home?

A mild fever may sometimes be managed safely at home. The goal of home care is to improve comfort, avoid dehydration, and support the body’s natural recovery process rather than eliminate the fever completely. Here’s what you can do: 

• Stay Hydrated: Drink plenty of fluids such as water, soups, oral rehydration solutions, and other non-alcoholic beverages to replace fluids lost through sweating and avoid dehydration⁷.
• Get Adequate Rest: Rest allows the body to focus its energy on fighting the underlying illness and recovering more quickly⁷.
• Wear Lightweight Clothing: Dress in light, comfortable clothing and avoid excessive blankets or heavy bedding, which can trap heat and make you feel hotter¹⁶.
• Keep the Room Comfortable: Stay in a cool, well-ventilated environment. If needed, use a fan to improve airflow, but avoid making the room excessively cold¹⁶.
• Try Lukewarm Sponging: A lukewarm sponge bath may help improve comfort in some individuals. However, avoid cold baths, ice packs, or alcohol rubs, as these can trigger shivering and may actually raise body temperature¹⁶.

Note: Home care measures help improve comfort. They should not replace appropriate medical treatment aimed at identifying and managing the underlying cause of the fever. 

When to Consult a Doctor?

Some situations require prompt medical evaluation to identify and address potentially serious underlying conditions. 

For Infants & Children 

Consult a doctor if your child¹⁶:

• Is under 3 months and has a fever. 
• Has a fever that lasts longer than expected for their age. 
• Experiences a febrile seizure (fever-related seizure). 
• Refuses to feed or drink fluids. 
• Shows signs of dehydration, such as reduced urination or a dry mouth. 
• Develops a new rash, unexplained bruising, or persistent vomiting. 
• Appears unusually sleepy, difficult to wake, inconsolable, or less responsive than usual. 
• Has difficulty breathing or a persistent cough. 
• Has recently travelled to another country or has a weakened immune system. 

For Adults 

Consult a doctor if you¹⁶:

• Have a fever above 39.4°C (103°F) that does not improve with fever-reducing medication. 
• Have a fever that persists for more than 48 to 72 hours or keeps recurring. 
• Develop a stiff neck, severe headache, or sensitivity to light. 
• Experience difficulty breathing, chest pain, or a persistent cough. 
• Feel confused, unusually drowsy, or have changes in mental status. 
• Develop a new rash or unexplained bruising. 
• Experience pain during urination or other symptoms suggestive of infection. 
• Have recently travelled to another country. 
• Have a weakened immune system or a chronic medical condition such as diabetes, heart disease, cancer, or chronic lung disease. 

Also Read: What Does It Mean When Fever Goes Away in a Day or Two 

Conclusion

Fever is often a sign that the immune system is actively responding to an infection or other health challenge. In many cases, it can be monitored and managed safely at home with supportive care. However, it is important to stay alert for warning signs and seek medical attention when symptoms are severe, persistent, or concerning. This will help to recognize when to manage a fever and when to escalate care, which can help ensure timely treatment and better health outcomes. 

Frequently Asked Question (FAQs)

References

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4. Temperature measurement: MedlinePlus Medical Encyclopedia. Accessed June 18, 2026. https://medlineplus.gov/ency/article/003400.htm 

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6. Temperature: Digital and Glass Thermometers. Accessed June 18, 2026. https://www.nationwidechildrens.org/family-resources-education/health-wellness-and-safety-resources/helping-hands/temperature-digital-and-glass-thermometers 

7. Australia H. Fever. June 2, 2026. Accessed June 12, 2026. https://www.healthdirect.gov.au/fever 

8. Fever in adults. NHS inform. Accessed June 12, 2026. https://www.nhsinform.scot/illnesses-and-conditions/infections-and-poisoning/fever-in-adults/ 

9. Fever in children. NHS inform. Accessed June 12, 2026. https://www.nhsinform.scot/illnesses-and-conditions/infections-and-poisoning/fever-in-children/ 

10. Abdel Wahab MF, Younis TA, Fahmy IA, el Gindy IM. Parasitic infections presenting as prolonged fevers. J Egypt Soc Parasitol. 1996;26(2):509-516. https://pubmed.ncbi.nlm.nih.gov/8754658/

11. Fever. Accessed June 12, 2026. https://medlineplus.gov/fever.html 

12. Galloway J, Cope AP. The ying and yang of fever in rheumatic disease. Clin Med. 2015;15(3):288-291. doi:10.7861/clinmedicine.15-3-288 https://europepmc.org/article/pmc/4953116

13. Brown I, Finnigan NA. Fever of Unknown Origin. In: StatPearls. StatPearls Publishing; 2026. Accessed June 12, 2026. http://www.ncbi.nlm.nih.gov/books/NBK532265/ 

14. Ogoina D. Fever, fever patterns and diseases called ‘fever’ – A review. J Infect Public Health. 2011;4(3):108-124. doi:10.1016/j.jiph.2011.05.002 https://pubmed.ncbi.nlm.nih.gov/21843857/

15. El-Radhi AS. Pathogenesis of Fever. Clin Man Fever Child. Published online January 2, 2019:53-68. doi:10.1007/978-3-319-92336-9_3 https://pmc.ncbi.nlm.nih.gov/articles/PMC7122269/

16. Fever: MedlinePlus Medical Encyclopedia. Accessed June 15, 2026. https://medlineplus.gov/ency/article/003090.htm 

17. Naito T, Mizooka M, Mitsumoto F, et al. Diagnostic workup for fever of unknown origin: a multicenter collaborative retrospective study. BMJ Open. 2013;3(12):e003971. doi:10.1136/bmjopen-2013-003971 https://pubmed.ncbi.nlm.nih.gov/24362014/

18. Świerczyńska M, Mirowska-Guzel DM, Pindelska E. Antiviral Drugs in Influenza. Int J Environ Res Public Health. 2022;19(5):3018. doi:10.3390/ijerph19053018 https://pubmed.ncbi.nlm.nih.gov/35270708/

19. Malaria. Accessed June 15, 2026. https://www.who.int/news-room/fact-sheets/detail/malaria 

20. Gawronska J, Koyanagi A, López Sánchez GF, et al. The Prevalence and Indications of Intravenous Rehydration Therapy in Hospital Settings: A Systematic Review. Epidemiologia. 2022;4(1):18-32. doi:10.3390/epidemiologia4010002 https://pubmed.ncbi.nlm.nih.gov/36648776/

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