Fever in Adults — When to Call a Doctor
Reading time: 5 minutesUpdated April 2026
Fever is a normal immune response — not a disease in itself. When is it helpful, when does it need action?
Temperature categories (adults)
- Normal: 36.5–37.4 °C
- Subfebrile: 37.5–38.0 °C
- Mild fever: 38.1–38.9 °C
- High fever: 39.0–40.0 °C
- Very high fever: above 40 °C (urgent)
How to measure properly
- Rectal: most accurate (gold standard)
- Oral: reliable in adults, under-tongue, 3–5 minutes
- Ear: quick, less accurate
- Forehead (skin): least accurate
- Avoid measurement right after eating/drinking or physical activity
When to call a doctor
- Fever above 39 °C lasting more than 3 days
- Fever with severe headache, neck stiffness (meningitis concern)
- Fever with confusion
- Fever with shortness of breath or chest pain
- Fever with flank pain (possible pyelonephritis)
- Fever with new rash — especially petechiae (do not blanch under pressure)
- Fever after travel to tropical regions
- Fever in immunocompromised patients (chemo, transplant, HIV)
Call 112 immediately for:- Fever above 41 °C
- Fever with unconsciousness or seizures
- Fever with petechial rash (sepsis concern)
- Fever with severe chest pain or breathing difficulty
At-home measures
- Fluids: 2–3 litres per day, warm tea or lukewarm water
- Paracetamol 1 g up to 4×/day or ibuprofen 400 mg up to 3×/day
- Rest; avoid alcohol
- Light clothing, cool room (not cold)
- Leg wraps (Wadenwickel) — wet, lukewarm (not cold) cloth on calves for 5–10 min
What the doctor can do on site
- Full clinical examination to find the source (lungs, throat, urine, skin, abdomen)
- Rapid tests: influenza, Covid, streptococcus, Mono
- Urine dipstick (suspected UTI/pyelonephritis)
- Blood draw for CRP, blood count, electrolytes — result same-day or next-day
- IV rehydration if needed
- Antibiotic or antiviral prescription when indicated
- Hospital referral for severe or unexplained fever
FAQ
When is adult fever dangerous?
Over 40 °C, persistent over 3 days, or with red-flag symptoms (confusion, petechial rash, severe headache, breathing difficulty).
Should I always lower fever?
Not always. Fever aids immunity. Treat for comfort if symptomatic. In heart failure, pregnancy, or at extremes (40 °C+), lower actively.
General information. Emergency: 112.
Sources: AWMF guidelines, DEGAM Fieber.