Fever — When Is It Dangerous (Adults & Children)?

Intro

Fever is a temporary rise in body temperature, usually due to infection. Most fevers are not dangerous by themselves, but how the person looks and associated symptoms matter. This guide helps you decide when to treat at home and when to seek urgent care.

Key Points

Typical fever: ≥38.0°C (100.4°F).
See a clinician urgently for red flags (below), regardless of the exact number.
In babies under 3 months, any fever ≥38.0°C warrants same-day medical review.
Hydration, comfort, and monitoring are more important than chasing a “normal” number.

What Counts as a Fever?

Oral/tympanic/temporal: ≥38.0°C (100.4°F)
Axillary (underarm): ~0.5°C lower than core readings; confirm with another method if high.

Red Flags — Seek Urgent Care Now

Any age:

Severe headache/neck stiffness, confusion, fainting, seizures.
Shortness of breath, chest pain, blue/gray lips or skin.
Severe dehydration (very dry mouth, no urine ≥8–12h), persistent vomiting.
Non-blanching rash (doesn’t fade when pressed), rapidly spreading rash.
Recent chemotherapy, transplant, long-term steroids, or immune problems.
Recent travel to malaria/dengue areas with fever.

Adults (≥18 years):

Temp ≥40.0°C (104°F) or ≥38.0°C lasting >3 days with no improvement.
Worsening pain in one area (chest, abdomen, back, flank, joints).

Children:

<3 months: Any fever ≥38.0°C (100.4°F) → urgent medical review.
3–6 months: ≥39.0°C (102.2°F) or looks unwell → same-day review.
Any age child: lethargic, inconsolable, stiff neck, labored breathing, poor intake/urine, seizure.

Common Causes

Viral infections (cold/flu, COVID-19, RSV).
Bacterial infections (ear/throat, pneumonia, urinary tract, skin).
Less common: inflammatory diseases, heat illness, medication reactions.

Home Care & Monitoring

Fluids: frequent small sips; breast/formula as normal for infants.
Comfort: light clothing, tepid room (avoid ice baths or alcohol rubs).
Medicine (if uncomfortable):
- Paracetamol/acetaminophen per label/doctor dose.
- Ibuprofen (if age-appropriate, not dehydrated, no kidney/stomach issues).
- Avoid aspirin in children/teens.
Recheck temperature and how the person looks every few hours.
Do not withhold food/fluids; focus on hydration and rest.

When to See a Clinician (Non-urgent but Soon)

Fever >3 days without clear source.
Recurrent fevers over weeks.
New localized symptoms (ear pain, sore throat, cough, urinary pain, skin redness).

How to Measure Accurately

Use a digital thermometer; follow the device’s instructions.
For infants, rectal or temporal artery readings are more reliable than underarm.
Take the reading after resting indoors for 15 minutes.

FAQ

Is the fever number itself dangerous?
Usually no — fever is part of the immune response. The cause and red flags guide urgency.

Should I alternate paracetamol and ibuprofen?
Only if advised by a clinician. Use one correctly dosed medicine first.

Can teething cause a high fever?
Teething may cause slight warmth, but not high fever. Look for other causes.