The three colours that need a call

Start here, because the rest of this page is reassurance and this part is not. The American Academy of Pediatrics names three colours that "always warrant discussion with your baby's doctor":

Red. The AAP: "Seeing red can mean blood, especially in the newborn period when your baby isn't eating or drinking anything red colored." It is often something minor — a small crack at the anus, or swallowed blood from delivery or from your own cracked nipples if you are breastfeeding — but the AAP's rule is that "any amount of bloody poop should be evaluated because it can be a sign of a problem."
Black, after meconium has finished. The AAP: "blood typically turns from red to black over time in the intestinal tract", so black poo later on is worth attention. The exception is explicit: this "does not apply to your baby's first few meconium bowel movements, which you can fully expect to be black and tarry looking".
White, pale, chalky or clay-coloured. The AAP: "White poop is quite rare but needs to be brought to the attention of a doctor as soon as possible. Pale poop that's lacking in color can be caused by an underlying liver problem. The earlier it is assessed, the better."

That last one is the one parents most often let slide, because a pale nappy does not look like an emergency. NICE's jaundice guideline CG98 makes the connection: in babies with jaundice lasting more than 14 days at term, or more than 21 days if born before 37 weeks, clinicians are told to look specifically for pale, chalky stools and dark urine that stains the nappy. Prolonged jaundice plus pale stools is the combination that gets investigated urgently, and both parts of it are things you can see at home.

The HSE's own trigger for contacting your GP or public health nurse is broader and easy to remember: get in touch if you notice a change in your baby's poo — for example if it is very smelly, pale, watery, harder, or contains blood.

The first days: meconium

The HSE describes it: "Your baby's poo will be sticky and green or black for the first few days. This is called meconium. This will then change to a yellow colour." The AAP calls it "this thick black or dark green substance" that filled the intestines before birth, and says that once it is passed, the stools turn yellow-green.

Meconium is nearly odourless, extremely sticky and hard to wipe. A smear of oil-free barrier cream on a clean bottom before the next nappy makes the following change easier, and there is nothing wrong with the stickiness.

The timing rule that matters

NICE's postnatal care guideline NG194 states that if a baby has not passed meconium within 24 hours of birth, this may indicate a serious disorder and requires medical advice. The AAP's threshold is a little later — if your baby does not pass meconium in the first 48 hours, "further evaluation is required to make sure that no problems exist in the lower bowel". Take the earlier number as your prompt to ask, not the later one.

After meconium: the normal range

The AAP's position is generous and worth quoting because it settles most of the anxiety on this page: "once your baby has pooped enough to get rid of the tarry meconium, all the varying shades of yellow, brown, and even green that may follow are considered perfectly acceptable."

Breastfed: the AAP describes "yellow liquid mixed with some particles that remind many parents of little seeds", and the shade of choice as mustardy yellow. The HSE says breastfed babies usually have runny nappies that do not smell.
Formula fed: the AAP says stools are usually tan or yellow, firmer than a breastfed baby's but "no firmer than soft clay". The HSE says formula-fed babies have more solid poo with a stronger smell. The AAP describes the formula-fed shade as yellow-tan with hints of green.
Green: the AAP is explicit that "green stools are not unusual, either, and they should not cause alarm". Digestion slowing down — for example with foods that take more effort to digest later on — can turn stools green.
Dark brown: the AAP notes that iron supplements can turn stools dark brown.
Changing between nappies: the HSE says a baby's poo "will probably vary from day to day or week to week", and to expect a change in texture, colour and smell after a new formula or any medicine.

How often is normal

The HSE's answer is deliberately wide: "Some babies have a dirty nappy after every feed. Other babies may only have a dirty nappy once a day, or every few days." And crucially: "Your baby is not constipated if their poo is soft, even if they have not pooed for 1 or 2 days." After the first few weeks of breastfeeding, some babies go several days.

The first weeks are different, though, because output is how feeding is judged. The NHS's guidance on whether a breastfed baby is getting enough milk uses nappies as a core signal, alongside weight gain and how your baby is behaving. If poos become infrequent or scanty in the first weeks, that is a feeding question rather than a bowel question, and it is worth raising with your midwife or health visitor early.

Wee, while we are here

The AAP's figures: a newborn may urinate "as often as every one to three hours or as infrequently as four to six times a day". A pink or brick-red stain on the nappy in the first week is usually concentrated urine rather than blood, and "as long as the baby is wetting at least four diapers a day, there probably is no cause for concern". Reduced urine output is an intermediate-risk amber sign in NICE's fever guideline NG143, so falling wet nappy counts always deserve a call.

Diarrhoea in a newborn

Because newborn stools are already soft and runny, diarrhoea is hard to spot. The AAP gives the tell: "a sudden increase in frequency (to more than one bowel movement per feeding) and unusually high liquid content in the stool." The concern is dehydration rather than the stool itself. NICE lists diarrhoea associated with dehydration among its red flags for serious illness in young babies.

When to call

Call your local emergency number (999 in the UK and Ireland, 911 in the US and Canada, 000 in Australia, 111 in New Zealand) if your baby:

Has diarrhoea with signs of dehydration, or is vomiting green or yellow-green.
Has a temperature of 38C (100.4F) or above, or below 36C (96.8F).
Looks pale, ashen, mottled or blue, or is unresponsive or unrousable.
Has a weak, abnormally high-pitched or continuous cry.
Is grunting, breathing over 60 breaths a minute, or drawing their chest in.
Has a bulging fontanelle, neck stiffness, a seizure, or a rash that does not fade under a pressed glass.

That list is NICE's own set of red flags for serious illness in young babies, from NG194.

Contact your midwife, health visitor, public health nurse or GP the same day if: there is blood in the nappy; the poo is black after the first few days; the poo is pale, white or chalky, especially with dark urine or yellow skin; your baby has not passed meconium within 24 hours of birth; wet nappies have dropped off; or the poo has become very smelly, watery or much harder.

What to let go of

Colour charts that grade nappies into a dozen shades mostly measure how recently your baby fed and how fast things moved. The AAP's summary covers almost every nappy you will ever open: yellow, brown and green are all fine. Keep your attention for red, black after meconium, and pale — and for your baby, who tells you more than the nappy does.

Newborn Poo Colour