Fever in Adults: Causes, Symptoms & Treatment
Fever in adults refers to a body temperature above 38 °C and is often a sign of infection. Learn about causes, symptoms, and treatment options.
Things worth knowing about "Fever adults"
Fever in adults refers to a body temperature above 38 °C and is often a sign of infection. Learn about causes, symptoms, and treatment options.
What Is Fever in Adults?
Fever in adults is defined as a body temperature exceeding 38.0 °C (100.4 °F). The normal body temperature of a healthy adult ranges between 36.5 °C and 37.5 °C. Fever is not a disease in itself but a symptom indicating an underlying cause – most commonly an infection or an inflammatory response of the immune system. It is considered a natural defense mechanism of the body.
Causes
Fever can be triggered by a wide variety of factors:
- Infections: The most common cause, including bacterial or viral infections such as the common cold, influenza, urinary tract infections, pneumonia, or COVID-19.
- Inflammatory conditions: Autoimmune diseases such as rheumatoid arthritis can cause fever.
- Medications: Certain drugs can cause fever as a side effect, known as drug fever.
- Vaccinations: A mild and temporary fever can occur after receiving a vaccine.
- Cancer: Certain malignancies, especially lymphomas, may be associated with fever.
- Heat stroke: Overheating of the body due to extreme environmental temperatures.
Symptoms
In addition to an elevated body temperature, fever is often accompanied by other symptoms:
- Chills and sweating
- Headache and body aches
- Fatigue and general weakness
- Loss of appetite
- Increased heart rate (tachycardia)
- Difficulty concentrating or mild confusion in cases of very high fever
Classification by Temperature
Fever is classified based on the measured body temperature:
- Low-grade fever: 37.5 °C – 38.0 °C
- Mild fever: 38.1 °C – 38.5 °C
- Moderate fever: 38.6 °C – 39.0 °C
- High fever: 39.1 °C – 40.0 °C
- Very high fever (hyperpyrexia): above 40.0 °C – a medical emergency
Diagnosis
Diagnosis begins with measuring body temperature – most accurately done rectally, but also possible orally, axillary (under the arm), or via the ear. The physician collects a thorough medical history and performs a physical examination. Depending on the suspected cause, additional investigations may follow:
- Blood count and inflammatory markers (e.g., CRP, white blood cell count)
- Urinalysis
- Swabs or cultures (e.g., throat swab)
- Imaging studies (X-ray, ultrasound) if specific conditions are suspected
Treatment
General Measures
For mild to moderate fever, supportive measures are recommended first:
- Adequate fluid intake: Drink plenty of water or herbal tea to compensate for fluid loss through sweating.
- Physical rest and bed rest
- Warm clothing during chills; cooling measures (e.g., cool damp cloths on the calves) for very high fever
Medication
Fever-reducing medications (antipyretics) are used when fever exceeds 39.0 °C or the patient is significantly unwell. Common active substances include:
- Paracetamol (acetaminophen) (well-tolerated, gentle on the stomach)
- Ibuprofen (additionally anti-inflammatory)
- Acetylsalicylic acid (aspirin) (not recommended for certain groups)
Treatment of the underlying cause is essential: bacterial infections are treated with antibiotics, while viral illnesses are typically managed symptomatically.
When to See a Doctor
Medical attention is urgently recommended in the following situations:
- Fever above 39.5 °C that does not decrease
- Fever lasting longer than 3 days
- Severe accompanying symptoms such as stiff neck, skin rash, shortness of breath, or confusion
- Fever in immunocompromised individuals or people with serious underlying conditions
- Recurrent fever without an identifiable cause
References
- World Health Organization (WHO): Fever – General Information. www.who.int
- Fauci, A. et al.: Harrison's Principles of Internal Medicine, 21st Edition. McGraw-Hill, 2022.
- National Institutes of Health (NIH) – MedlinePlus: Fever in Adults. www.medlineplus.gov
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