Fever and Diarrhoea During Teething: What to Do

The belief that teething causes fever and diarrhoea is one of the stickiest pieces of received parenting wisdom. It also has a long track record of leading to delayed diagnosis of genuinely treatable illness. Knowing what teething does and doesn't do is one of the more practically useful things a parent of a six-month-old can learn. For a wider view, see our complete guide to child health.

Why the Belief Exists

The teething window — broadly 4 to 24 months, with peak activity 6–18 months — overlaps almost perfectly with the period when:

• Maternal antibody protection wanes from around 6 months, leaving babies meeting their first wave of viruses without inherited cover
• Viral gastroenteritis (rotavirus before vaccination, norovirus, adenovirus) is at its most common
• Acute otitis media (ear infections) peaks
• Babies put everything in their mouths as part of normal sensorimotor exploration, sharply increasing exposure to pathogens
• Roseola, hand-foot-and-mouth, and the first respiratory viruses all start showing up

So fever and diarrhoea genuinely do happen during the teething period — just not because of teething. The correlation is real; the causation is not. It's a textbook case of two common things sharing a timeline.

What the Evidence Actually Shows

Multiple controlled prospective studies have followed babies through the teething period, recording symptoms day by day and correlating them with confirmed tooth eruptions. The consistent findings:

• Mild temperature elevations (below 38°C) sometimes occur in the immediate 24–48 hours around tooth eruption — this is a real but small effect, probably from local inflammation
• Fever of 38°C or above is not caused by teething in any study with adequate controls
• Diarrhoea is not associated with teething when other causes are systematically considered
• Runny nose, cough, and rash are not associated with teething
• Reduced appetite and irritability are loosely associated with eruption days

The American Academy of Pediatrics, NICE, and major international paediatric organisations all state clearly that fever and diarrhoea coinciding with teething warrant assessment for another cause. This isn't a scientific minority view — it's the consensus.

What to Do About Fever in a Teething Baby

Treat the fever as a fever, not as a teething symptom.

Take the temperature accurately:

• Axillary (under the arm) digital thermometer — first-line for babies under 4 weeks and recommended in NICE guidance for children under 5
• Tympanic (ear) thermometer — fine in babies over 4 weeks, but not in the under-4-weeks
• Avoid forehead strips — they're inaccurate enough to mislead

Then act on the threshold:

• Under 3 months, any temperature ≥38°C — same-day medical assessment. Always. Even if the baby looks otherwise well. Even if you can see a tooth coming through.
• 3–6 months, ≥39°C — same-day assessment. 38–39°C in this age group needs assessment if there are any other concerning signs or if it persists more than 24 hours.
• Over 6 months, fever managed at home with paracetamol or ibuprofen for comfort, plus prompt assessment if any of: rash (especially non-blanching), persistent vomiting, refusing fluids, breathing changes, unusual drowsiness, fever lasting more than 48 hours without improvement, or just a sense the child is significantly unwell.

If a teething baby has a fever, the most likely actual diagnosis is a coincidental viral illness — usually self-limiting, but some need treatment, and a proportion turn out to be UTIs, ear infections, or other bacterial issues that benefit from being caught.

What to Do About Diarrhoea in a Teething Baby

Diarrhoea in a teething baby is almost always gastroenteritis or another GI cause.

Practical management:

• Maintain hydration. Continue normal feeds — breastfeeds, formula, or milk. There is no evidence that withholding milk improves recovery; the WHO and NICE both recommend continued feeding through diarrhoea.
• Oral rehydration solution (ORS) — Dioralyte or similar — for babies who are losing significant fluid. Small frequent sips beat large boluses.
• No anti-diarrhoeal drugs in young children — they prolong the illness by trapping pathogens in the gut.
• No antibiotics for typical viral gastroenteritis. Most paediatric diarrhoea is viral.

Get medical advice if:

• Diarrhoea is severe or prolonged (more than 5–7 days)
• It contains blood or mucus
• There's vomiting frequent enough that fluids aren't staying down
• Signs of dehydration: fewer than 4 wet nappies in 24 hours, sunken fontanelle in a baby, dry mouth, no tears with crying, marked lethargy or irritability
• The child is significantly unwell beyond the diarrhoea

The Real Danger

The hazard of attributing every symptom to teething isn't that the baby gets a few extra days of paracetamol — it's that genuine illness gets missed. Cases of meningitis, sepsis, UTI, and acute otitis media being initially passed off as teething are a recurring theme in paediatric case reports.

Teething can sit in the picture; it just can't be the explanation for fever, diarrhoea, vomiting, rash, or significant illness. When in doubt, have the baby seen — and don't let "she's been teething" be the reason you delay.

Teething does not cause fever above 38°C, diarrhoea, or any significant illness. The misconception is fuelled by timing — between 6 and 12 months babies are teething and also losing maternal antibodies, exploring with their mouths, and meeting their first viruses, ear infections, and gastroenteritis. A mild temperature elevation under 38°C around an eruption is occasionally seen; anything higher needs a separate diagnosis. In a baby under three months, any fever is same-day. In babies 3–6 months, fever above 38°C needs same-day review. The real risk is the opposite of what most parents fear: serious infections being attributed to teething and missed.