Symptom

Fever in Adults: What Temperature Is Dangerous?

Fever is the body's defence against infection. Most fevers are self-limiting — but certain patterns signal serious conditions that need urgent care.

Normal temperature
36–37.5 °C (96.8–99.5 °F)
Fever defined
>38 °C (100.4 °F)
Hyperpyrexia
>41 °C — emergency
Most common cause
Viral infection
Seek Emergency CareFever above 40 °C, confusion or altered consciousness, stiff neck + photophobia + rash (meningitis), fever in immunocompromised patient, or sepsis signs (rapid breathing, cold mottled skin).

Causes by Fever Pattern

PatternLikely Cause
Sudden, high, with cough/sore throatInfluenza, pneumonia, COVID-19
Fever + dysuriaUrinary tract infection (pyelonephritis)
Fever + headache + neck stiffnessBacterial meningitis — emergency
Fever after travel abroadMalaria, typhoid, dengue
Prolonged fever (>3 weeks)TB, lymphoma, endocarditis, abscess, brucellosis
Fever + joint pain + rashViral arthritis, lupus, reactive arthritis
Fever in immunocompromised patientNeutropenic sepsis — emergency
Fever TreatmentParacetamol or ibuprofen lower fever and ease discomfort. Drink plenty of fluids. Tepid sponging may help comfort. Do NOT use aspirin in adults with viral illness (risk of Reye's syndrome).

Fever vs Infection

A fever is a symptom, not a diagnosis. The goal is identifying the underlying infection or cause, not just suppressing the temperature. If fever persists >5 days despite treatment, seek review.

What temperature is a fever in adults?
A temperature above 38 °C (100.4 °F) is defined as fever. Above 39.5 °C is high fever; above 41 °C (hyperpyrexia) is a medical emergency.
Should I take paracetamol or ibuprofen for fever?
Both work. Paracetamol is preferred if you have stomach issues or are taking blood thinners. Ibuprofen has the advantage of reducing inflammation. They can be alternated every 4 hours if needed.
When does a fever need antibiotics?
Only bacterial infections respond to antibiotics. Most fevers are viral and do not benefit from antibiotics. Your doctor will assess whether bacterial infection is likely before prescribing.
Can you have a fever without infection?
Yes — heat stroke, certain medications (drug fever), autoimmune diseases, malignancy (especially lymphoma), and pulmonary embolism can all cause fever without infection.
Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.