A mild–moderate fever usually is not dangerous and can help fight infection. A fever becomes more concerning when it is very high, lasts a long time, or comes with “red flag” symptoms like confusion, trouble breathing, or a stiff neck.
Temperature thresholds
- In healthy adults, a fever over about 103–104 °F (39.4–40 °C) should be checked by a clinician, especially if it does not improve with fluids and fever medicine.
- Fevers above about 105–106 °F (40.5–41 °C) are considered dangerous because they can start to damage organs if not treated promptly.
Age-specific danger points
- Any fever of 100.4 °F (38 °C) or higher in a baby under 3 months needs urgent medical evaluation.
- In older children, sustained fevers around 102–104 °F (38.9–40 °C) or higher, especially if they do not respond to medicine or the child looks very unwell, require prompt medical care.
Warning signs with any fever
Seek emergency or urgent care (for adults or children) if a fever is accompanied by:
- Confusion, difficulty waking, seizure, stiff neck, severe headache, trouble breathing, chest pain, or a purple or rapidly spreading rash.
- Persistent vomiting, inability to drink or pee, signs of dehydration (very dry mouth, no tears, sunken eyes), or severe pain anywhere.
Special risk groups
- People with heart or lung disease, weak immune systems, very young children, and older adults can be harmed by lower fevers than healthy adults and should seek care sooner.
- For elderly adults, even a temperature above about 102 °F (38.9 °C) or a clear change from their usual baseline can be dangerous.
If you or someone else has a fever and any of the red-flag symptoms above, or if you are unsure, treat it as an emergency and contact a doctor or local emergency services immediately.