The first 24 hours of a fever
Most childhood fevers follow a recognisable shape. The first day is the messy one — temperature climbing, behaviour changing, and a lot of unanswered questions. Day two is usually calmer because by then you know what you're dealing with.
Here's an hour-by-hour playbook for that first 24 hours: what to do, what to watch for, and when to stop watching and start calling.
The quick answer
- Hour 0: take temperature, note time, offer fluids, decide whether a dose is needed for comfort.
- Hours 1–6: medicine starts working ~30 minutes in. Re-check at the 1-hour mark and again at the 4–6 hour mark.
- Hours 6–12: the picture is forming. Are they drinking? Wet nappies? Other symptoms?
- Hours 12–24: peaks often happen overnight. Don't routinely wake a sleeping child.
- If any red flag appears at any hour — non-blanching rash, breathing trouble, drowsiness, blue lips, a fit — stop reading and call 999 or 111.
Hour 0: the first reading
Your child feels hot, or is grumpy, or refused dinner. You reach for the thermometer.
- Take the temperature with a reliable device — electronic underarm or tympanic (ear). Forehead strips and oral thermometers are not recommended for young children.
- Note the time and the reading. 38.4°C at 19:10 is the foundation of everything that follows.
- Don't strip them off; don't over-bundle them. Normal indoor clothes, normal duvet. A feverish child still needs to be comfortable, not extreme in either direction.
- Offer a drink — small sips, often. Milk, water, diluted squash, breastmilk. Whatever they'll take.
- Decide on medicine based on how they look, not just the number. See "Hour 0 decision" below.
Hour 0 decision: medicine or not?
The NHS-supported principle: medicine treats discomfort, not the thermometer reading. A useful split:
| Looks like… | Medicine? |
|---|---|
| Warm, slightly grumpy, still playing, drinking | Probably not yet — wait, fluids, monitor |
| Hot, miserable, won't be put down, refusing drink | Yes — paracetamol or ibuprofen |
| Sleeping peacefully | No — sleep is doing more for them than Calpol |
| Limp, floppy, hard to rouse | Take temp + call 111 / 999 depending on age |
If giving medicine, log it: name, ml, time. Day-one over-dosing usually happens not from one big mistake but from two parents quietly giving the same dose 90 minutes apart.
Hours 1–6: the first wave
Once a dose is on board:
- Paracetamol takes effect in about 30 minutes, peaks at 60–90 minutes, lasts 4–6 hours
- Ibuprofen is a touch slower — 30–60 minutes to start working, peaks around 1–2 hours, lasts 6–8 hours
What to do during this window:
- Re-check temperature at the 1-hour mark. A drop of ~1°C is normal and welcome; less than that doesn't mean the medicine failed — comfort matters more than the number.
- Keep offering small drinks every 15–20 minutes when awake
- Make them comfortable — somewhere cool but not cold, dimmed light, favourite blanket or toy
- Don't sponge with cold water or use cooling fans — NICE explicitly advises against. It causes shivering, which raises core temperature.
- Watch for the medicine wearing off at the 4-hour mark. Don't pre-dose just because the clock allows it — wait until discomfort returns.
Hours 6–12: the picture forms
By this point you're roughly half a day in and the shape of the illness should be becoming visible. Ask yourself:
- Are they drinking? Wet nappies in the last 6 hours? Wee colour pale?
- What other symptoms? Cough, runny nose, sore throat, rash, vomiting, ear pulling? The accompanying symptoms tell you more about the cause than the temperature does.
- How responsive are they? Making eye contact, recognising you, smiling occasionally is reassuring. Glazed, unresponsive, not consolable is not.
- Is the temperature trending up or down between doses? A typical viral fever spikes higher in the early evening and settles overnight.
If at any point you tick boxes from the red flag list — non-blanching rash, fast breathing, drowsiness, mottled skin, dehydration signs — stop monitoring and start calling.
Hours 12–24: the first night
Fevers often peak in the late evening — this is normal cortisol rhythm. Don't be alarmed if 8pm gives you the highest reading of the day.
Going into the night:
- Give a dose before bedtime if they're still uncomfortable. Ibuprofen lasts longer (6–8 hours) than paracetamol (4–6) so is often a sensible bedtime choice — though give it after food.
- Don't routinely wake a sleeping child just because the next dose window opens. See should you wake a sleeping child to give Calpol?
- Keep the thermometer to hand — if they wake distressed, take a reading first before deciding on action.
- If you'll need to be up checking, set a soft phone reminder — even just once at the 4-hour mark — so you actually wake up and don't just listen anxiously from your own pillow.
The 24-hour mark: what to make of it
By the end of day one, you should have:
- A rough picture of the temperature range (e.g. "37.8–39.2, spiking in the evening")
- A count of how many doses you've given and when
- A sense of whether they're managing fluids
- A sense of other symptoms — is this clearly a cold, or something less obvious?
Most viral fevers improve from day 3 onwards. If your child is improving by 24 hours, brilliant. If they're stable, that's also reasonable. If they're getting worse — climbing temperatures, less responsive, refusing fluids, new symptoms — that's a call-the-GP day.
What you don't need to do
A few things often added to the first-day playbook that the evidence doesn't really support:
- Tepid sponging or cool baths. NICE advises against — causes shivering, which raises body temperature.
- Stripping a child down to a nappy "to bring the temperature down". Just makes them shiver.
- Vitamin C and "immune boosters". No good evidence they shorten viral illness in children.
- "Sweating it out" under extra blankets. Unhelpful and can be dangerous.
- Routinely waking for medicine. Sleep > medicine for viral fever, unless distressed.
Frequently asked questions
What do I do in the first hour of my child's fever?
Take a temperature with a reliable thermometer. Offer fluids. Decide whether a dose is appropriate for comfort, not for the number. Note the time and any dose. Watch them.
Should I give Calpol straight away?
Only if your child is uncomfortable. Medicine treats discomfort, not the reading. A cheerful child with 38.5°C doesn't necessarily need a dose.
How often should I check temperature?
Every 2–4 hours during the day. After a dose, check at the 1-hour mark. Less often if they're sleeping comfortably.
Should I be more worried at night?
Fevers often peak in the evening — this is normal. The "fever's worse at night" feeling is partly that you have less to distract you from it.
When does day 1 turn into a doctor visit?
If your child is under 3 months with any fever, call 111 immediately. Otherwise, if temperature is climbing despite doses, if they're getting more drowsy, if fluids are minimal, or if any red flag appears — call.
Can I send my child to school or nursery the next day?
If they've still had a fever in the last 24 hours, no. The general guidance is 24 hours fever-free without medicine before returning.
How Dosey helps
Dosey is designed for exactly this 24-hour window. Log a temperature in two taps, log a dose in two taps, and the home screen shows: last temperature, next-dose-time, and a clear timeline of what's been given. Two parents on the same picture, no doubling up at 3am.
This isn't medical advice. If you're unsure at any point in the first 24 hours, call NHS 111. It's free and available all night.
Related posts
- When should I see a doctor for a child's fever?
- Should you wake a sleeping child to give Calpol?
- Tracking a cold or fever with a young child