You open the nappy, and there it is. A patch of green. Enough to make any parent pause mid-change. Here is the reassuring bit: green baby poo is very common, and most of the time it is nothing to worry about. Baby poo spans a wide range of normal shades, and mustard yellow, orange, brown and green all sit inside it. This guide covers what green poo can mean for breastfed and formula-fed babies, the causes parents ask about most, and the signs worth a GP visit.
Important Notice
Breastfeeding is best for babies. Breastmilk provides the ideal balanced diet and protection against illness for your baby. We fully support the World Health Organisation’s recommendation of exclusive breastfeeding for the first six months of life.
What is green baby poo?
Green baby poo is just what it sounds like: poo with a green tint, anywhere from pale olive to deep forest.
The colour usually comes down to bile, a greenish-yellow fluid made in your baby's liver that helps break down fat. As milk moves along the gut, bile shifts from green to yellow to brown. When things move through quickly, there is less time for that shift, so the poo arrives still green.
Green often just means milk travelled through faster than usual. That is a normal part of how small digestive systems work.
What does normal baby poo look like?
Normal covers a lot of ground. Your baby's poo changes over the first few weeks, then keeps shifting as they grow and start solids.
The first few days
Your baby's first poo is meconium. The NHS describes it as sticky and greenish-black, and most babies pass it within the first 48 hours.
Over the next few days it lightens, moving from black to green, then brown, before settling into a paler yellow. Green in the first week is expected.
Breastfed babies
The NHS says breastfed babies' poo is usually runny, yellow or mustard, and does not smell much. In the early weeks your baby may poo at every feed. After around six weeks, some go days without one. Both are normal.
Formula-fed babies
Formula-fed poo tends to be firmer, darker brown and smellier, says the NHS. Some babies poo up to five times a day at first, easing to about once a day after a few months. A mustard or greenish tinge is common.
Causes of green baby poo
Green poo has a long list of possible causes. Here are the ones we hear about most:
Mum's diet
If you are breastfeeding, what you eat can turn up in the nappy. Green leafy vegetables such as spinach, kale and broccoli are the usual suspects, along with foods containing green colouring. The effect is temporary and harmless, and usually passes within a day or two. This is not a reason to cut out vegetables: spinach on your plate is a good thing.
Baby's diet
Once weaning starts, the nappy becomes something of a menu. Peas, spinach, courgette and broccoli can all turn poo green within a day. Early on you may even spot food coming out looking much as it went in.
Iron plays a part too. Iron-rich foods and iron drops can darken poo to a deep green, or close to black. Our guide to iron-rich foods for babies has more, and our guide to weaning your baby covers the first few weeks.
A change of milk
Switching formula often changes poo colour, texture and frequency for a while. Green or darker poo during a changeover is common, partly because formula is fortified with iron. A gradual switch across 7 to 14 days tends to be gentler on tiny tummies, and our guide to introducing a new follow-on formula explains how to pace it. Moving from breast to formula shifts things too. The NHS notes poo becomes darker and more paste-like.
Fast milk flow in breastfed babies
Bright green, frothy poo in a breastfed baby is often about speed. This is usually when milk moves through their gut more quickly than usual, often because there's a strong milk flow or oversupply.
You may have read the colour of baby’s poo is linked to a foremilk and hindmilk imbalance. That framing is out of date. The fat content of breast milk rises gradually through a feed, with no switch that flips partway. What can happen is that a baby with a plentiful supply takes in a lot of milk quickly, speeding up gut transit.
If your baby is settled and gaining weight, there is usually nothing to fix. If feeds feel uncomfortable, a breastfeeding counsellor can help, and our post on overcoming breastfeeding challenges is a good start.
When to see a doctor
Green poo on its own, in a baby who is feeding well, comfortable and gaining weight, is rarely a reason to worry. What matters is the company it keeps.
Speak to your GP or health visitor if you notice:
- Green, frothy poo alongside a lot of crying after feeds, wind, reflux or a rash, especially if the pattern keeps repeating
- Very pale or chalky poo. NHS guidance is to seek medical advice, as it can be a sign of a liver problem
- Black poo once the meconium days have passed
- Blood in the nappy, beyond the first few days of life
- Mucus in the poo that is persistent or unexplained
- Poo that is very watery, much more frequent than usual, or unusually smelly
- Your baby is not gaining weight, refusing feeds, or simply seems unwell
Trust your instincts. NHS advice is not to delay when you are worried, and you will never be wasting a health visitor's time.
The takeaway
Green baby poo looks alarming and usually is not. Normal poo can range from mustard yellow to green, and things like bile, faster digestion, a change in milk or even eating spinach can temporarily change its colour.
What matters more than the shade is your baby. Feeding well, settled and growing? You are almost certainly fine. Green poo plus crying, blood, mucus or weight worries? That is a call worth making.
Understanding your baby’s poo is just one of those things you get used to surprisingly fast as a parent. At Kendamil, we hear from plenty of parents squinting into nappies at 3am. You are in good company.
Green baby poo FAQs
Why is my baby's poo green?
Most green baby poo is caused by bile moving through the gut quickly, before it has time to turn brown. Green vegetables, iron in formula or supplements, a change of milk and routine jabs are other common causes. It is usually temporary.
Is green baby poo normal?
Yes, and it is very common. The healthy range runs from mustard yellow through orange and brown to green. It becomes worth investigating when it arrives with other symptoms, such as blood, persistent mucus or a lot of crying after feeds.
What does dark green baby poo mean?
Dark green baby poo is most often down to iron, from fortified formula, iron drops or iron-rich first foods. In the first 48 hours, very dark greenish-black poo is meconium, which is expected. Black poo after that stage should be checked by a GP.
Does green poo mean my baby has CMPA?
Rarely on its own. CMPA usually shows as a cluster of symptoms, which can include reflux, diarrhoea, constipation, eczema, mucus or blood in the poo, and frequent unexplained crying. Only a GP or health visitor can assess whether it is behind your baby's symptoms.
How long does green baby poo last?
Green poo caused by diet, a change of milk, immunisations or a mild bug usually settles within a few days. If it carries on for more than a week or two, or comes with other symptoms, mention it to your health visitor or GP.
Medical Disclaimer
The information contained in this article is for educational and informational purposes only and does not constitute medical advice. Always consult your GP, health visitor, or a qualified healthcare professional if you have any concerns about your baby's health or feeding routine.
