Baby health basics: what's normal, what's not

Most of what worries new parents in the first year turns out to be normal. Newborns grunt, twitch, change colour, and produce alarming-looking nappies — and the vast majority of the time, this is biology working exactly as it should. The hard part is knowing which signals can wait and which ones need a phone call right now.

This guide covers the most common health questions in the first year, with a deeper article linked for every topic. If you're not sure where to start, the single most useful rule is this: the younger your baby, the lower your threshold should be for calling a doctor. A concern that could wait in a 9-month-old may need same-day attention in a 2-month-old, and emergency action in a newborn.

Trust your instinct — with thresholds alongside it

You know your baby. A change in their normal behaviour, a cry you haven't heard before, unusual limpness or stillness — that instinct is worth acting on. "Worried well" visits to a GP or a call to 111 are not a waste of time; they are the system working correctly. No healthcare professional will judge you for calling when you weren't certain.

At the same time, concrete thresholds matter. Instinct alone can swing in both directions — worrying about normal things while under-responding to genuine signals. The articles in this cluster give you specific temperatures, ages, and symptom combinations that change the urgency tier. Thresholds and instinct work together; neither is sufficient on its own.

Newborn jaundice

Yellow skin and yellow eyes in a newborn are almost always jaundice — a buildup of bilirubin as the baby's liver processes the breakdown of old red blood cells. Around 60% of newborns develop some degree of jaundice.³ In the majority of cases it is physiological: a normal, temporary process that peaks around days 3–5 and resolves within two weeks without treatment.

Jaundice spreads in a predictable direction — face first, then chest, abdomen, and legs. Mild facial jaundice in an otherwise well, feeding baby is usually monitored rather than treated. But jaundice that starts in the first 24 hours, spreads rapidly to the palms and soles, or comes with any sign of illness is a different matter — this can indicate a pathological cause that needs urgent assessment.

The key with jaundice is not to dismiss it because it is common. Severe untreated jaundice can cause kernicterus, a form of brain damage that is entirely preventable with timely phototherapy. Know the red flags, and report any visible yellowing to your midwife rather than waiting.

→ Deep dive: Newborn jaundice: types, thresholds, and red flags

Fever: what the temperature actually means

Fever is defined as a temperature of 38°C (100.4°F) or above, regardless of how it is measured.¹ In babies under 3 months, any fever at this threshold is a medical emergency — not because the fever itself is uniquely dangerous, but because the immature immune system cannot reliably contain infection, and the risk of missing a serious bacterial illness is too high to take chances with.²

For older babies the picture shifts. A 7-month-old with a temperature of 38.5°C who is alert, feeding reasonably, and has no other concerning symptoms is a very different situation from a 6-week-old with any fever at all. After 6 months, how your baby is acting — responsiveness, eye contact, consolability — matters as much as the number.

How you take the temperature also matters. Axillary (armpit) thermometers are the most practical for home use. Tympanic (ear) thermometers are reliable from 6 months. Forehead strips are not reliable enough to base a clinical decision on — if you're deciding whether to call 111, use a digital thermometer.

→ Deep dive: Baby fever: when to worry and when to wait

Colic and the witching hour

Colic is one of the most used — and most misunderstood — words in newborn parenting. Clinically, it means crying for more than 3 hours per day, more than 3 days per week, for more than 3 weeks, in an otherwise healthy, well-feeding, normally growing baby.⁴ Somewhere between 10% and 40% of babies meet these criteria at some point. Peak distress typically arrives around 6 weeks of age. Almost all colic resolves by 3–4 months, regardless of what parents do or don't do.

What causes colic is not fully understood. Gut immaturity, altered microbiome, overstimulation, and temperament have all been proposed; none has conclusive evidence. Practically, this means there is no universal fix — but there are strategies that help many babies, including rhythmic motion, white noise, swaddling, and reducing stimulation.

The witching hour is related but distinct: a pattern of fussiness that occurs predictably in the late afternoon or evening. It is extremely common in the first three months and is often not colic — just a recognisable daily pattern of unsettled behaviour that most families find eases by 3 months.

→ Deep dive: Colic and the witching hour: what helps

Teething

Teething begins when the first tooth erupts through the gum — typically the lower central incisors, around 6–10 months, though anywhere from 4 to 12 months is normal variation. The process continues until roughly age 3, when the last baby molars usually appear.

Real teething symptoms are limited: increased drooling, gum swelling, increased chewing, and mild irritability around the days of tooth eruption. A slight rise in temperature is occasionally reported, but true fever — 38°C or above — is not caused by teething.⁵ If your baby has a fever during teething, the teething is coincidental and the fever needs to be assessed on its own terms.

Several popular "remedies" carry safety warnings. Amber teething necklaces present documented strangulation and choking risks (FDA warning). Benzocaine gels are not safe for infants under 2 years (FDA warning). Homeopathic teething tablets have been recalled. Chilled — not frozen — teething rings and gentle gum massage are the evidence-supported options.

→ Deep dive: Teething: symptoms, safe relief, and what to avoid

When to call the doctor

Knowing when to escalate is one of the most practically important skills in the first year. The answer sits on a scale: from "can wait for a routine appointment" through "call 111 today" all the way to "call 999 right now." Having the tiers in mind before a crisis reduces the cognitive load in the moment.

Emergency signals — blue lips, inability to rouse, persistent breathing difficulty, or a rash that doesn't fade under glass pressure — always mean calling 999 or going to A&E. The non-blanching rash test (press a clear glass firmly against the rash: if it doesn't fade, assume meningitis until proven otherwise) is one every parent should practise knowing before they need it.⁶

Below emergency: fever in any baby under 3 months, signs of dehydration, a fontanelle that is bulging or sunken, projectile or bile-stained vomiting, or any situation where your gut says something is significantly wrong. Call 111, your GP, or your midwife.

→ Deep dive: When to call the doctor: a tier guide for the first year

Stool changes: a quick health signal

Your baby's nappies are surprisingly useful clinical data. Colour, consistency, and frequency all shift predictably with age and feeding type — and a sudden change in pattern can be an early sign of illness, dietary change, or dehydration. Breastfed newborns typically have soft, seedy, mustard-yellow stools multiple times a day, which firm up once solids begin. Formula-fed babies tend toward firmer, tan-coloured stools from the start.

Constipation in babies is defined more by texture than frequency. A breastfed baby who hasn't pooped for several days may be perfectly fine — a baby producing hard, pellet-like stools every day is constipated. The pattern that matters is a change from your baby's usual baseline.

Blood in the stool — whether bright red from an anal fissure, or darker — always warrants a call to your GP. The same goes for stools that are pale, chalky, or clay-coloured (which can indicate liver issues), or very watery stools alongside signs of dehydration.

→ Deep dive: The Bristol stool scale for babies: what's normal, what's not

General red flags at any age

Regardless of which specific symptom you're dealing with, certain signals always override "watch and wait":

The goal of this cluster is not to make you more anxious — the opposite. Concrete thresholds reduce the cognitive load of deciding whether to call. If your baby doesn't meet the threshold, you can monitor with confidence. If they do, the decision is already made.

Sources

1. NHS. "High temperature (fever) in children." NHS, 2024. https://www.nhs.uk/conditions/high-temperature/
2. American Academy of Pediatrics. "Fever and Your Baby." HealthyChildren.org. https://www.healthychildren.org/English/health-issues/conditions/fever/Pages/Fever-and-Your-Baby.aspx
3. NHS. "Newborn jaundice." NHS, 2023. https://www.nhs.uk/conditions/jaundice-newborn/
4. NHS. "Colic." NHS, 2023. https://www.nhs.uk/conditions/colic/
5. NHS. "Teething." NHS, 2023. https://www.nhs.uk/conditions/teething/
6. NHS. "Meningitis." NHS, 2024. https://www.nhs.uk/conditions/meningitis/