Overview
A fever is a temporary rise in body temperature above 38 degrees Celsius (100.4 degrees Fahrenheit) as part of the body's immune response to infection or illness. Fever itself is not a disease but a symptom. In most cases it is helpful, as higher temperatures hinder the growth of many pathogens.
How common is it?
Fever is one of the most universal medical symptoms and is among the most common reasons parents seek medical advice for their children.
Causes and risk factors
Infections of virtually any type can trigger fever as the immune system releases inflammatory chemicals (pyrogens) that signal the hypothalamus in the brain to raise body temperature.
Common risk factors
- Viral infections (commonest cause: cold, flu, COVID-19)
- Bacterial infections
- Inflammatory conditions (rheumatoid arthritis, IBD)
- Certain medications (drug fever)
- Vaccines (normal and expected)
- Malignancy in rare cases
- Heat stroke (high temperature without true fever)
Symptoms
- Temperature over 38°C
- Shivering and chills
- Sweating
- Headache
- Muscle aches
- Fatigue and weakness
- Loss of appetite
- Flushed face and hot skin
When to see a doctor
In adults: seek care for fever over 39.5°C, fever lasting more than 5 days, or fever with rash, stiff neck, sensitivity to light, severe headache, or breathlessness. In children under 3 months: any temperature over 38°C needs urgent review.
Diagnosis
Temperature measurement confirms fever. Further investigation depends on clinical context: blood count, urine, throat swab, chest X-ray, and blood cultures guide identification of the cause.
Treatments
Antipyretic medication
Paracetamol or ibuprofen lower fever and relieve discomfort. The goal is comfort, not necessarily a normal temperature. Do not alternate automatically; use whichever works.
Cooling measures
Drink plenty of cool fluids. Dress lightly. Tepid sponging provides marginal benefit. Avoid cold baths which cause shivering and raise temperature.
Treating the underlying cause
Antibiotics for confirmed bacterial infection. Antiviral treatment for specific viral infections (flu, COVID-19). Supportive care for self-limiting viral illness.
Self-care and lifestyle
- Stay well hydrated as fever increases fluid losses significantly
- Rest and allow the body to direct energy to immune function
- Monitor for worsening symptoms or new symptoms in yourself or your child
- Do not wrap up a feverish child in extra clothing or blankets
Prevention
Vaccinations prevent many fever-causing infections. Good hand hygiene reduces transmission of respiratory and gut viruses.