Green is the colour that sends more parents to the internet at two in the morning than any other, and it's almost always nothing.
Understand why it happens, though, because one particular explanation for it has been repeated so widely and so confidently that it has changed how people feed their babies, and it's largely wrong.
Why does stool turn green?
Bile. Bile is green when it leaves the liver and it turns yellow-brown as it passes through the gut and is broken down by bacteria. So green stool means it moved through faster than usual and the bile didn't have time to change colour.
That's the entire mechanism, and everything that causes green stool causes it by speeding transit up.
- Iron-fortified formula, which very commonly produces dark green stool and is entirely harmless.
- A cold or a mild tummy bug, which speeds things along.
- Teething, which does the same via the extra saliva being swallowed.
- The transitional days in the first week, when green-brown is the expected stage.
- Something the breastfeeding mother ate, particularly a lot of green vegetables.
- Starting solids, when almost any colour turns up for a while.
- Occasionally a reaction to something, in which case there's more going on than colour.
| Cause | What you would also see | Action |
|---|---|---|
| Transitional stool, days 3-4 | Turning yellow within a day or two | None |
| Iron in formula | Consistent, dark green, otherwise well baby | None |
| Fast let-down or oversupply | Frothy green, gulping at the breast, plenty of wind | Feed one side per feed; consider laid-back positions |
| Feeding on both sides too quickly | Green frothy stool, unsettled baby, good weight gain | Let her finish the first side first |
| A cold or a virus | Snuffles, off feeds, resolves in days | Watch hydration |
| Green vegetables or spinach, after solids | Obvious in timing | None |
| Teething | Drooling, dribble rash, more frequent stools | None |
The frothy green one, explained properly
This is the foremilk-hindmilk imbalance, and it's the piece of advice I'd most like to correct. The story goes that the watery milk at the start of a feed is low in fat, the creamier milk later is high in fat, and a baby who gets too much of the first will produce frothy green stool and be unsettled. The recommended fix is to feed from one breast only for several feeds in a row. The mechanism is real up to a point. Fat content does rise through a feed. What isn't right is the idea that it's a common problem requiring intervention, because fat content varies with how full the breast was and with the time since the last feed, and across a day a baby who feeds responsively gets what she needs regardless of how any single feed went. Block feeding to fix it can reduce supply, and it's prescribed far more often than it's warranted.
Frothy green stool with an unsettled baby is much more often oversupply, or a fast let-down, or simply a normal week. If it's happening persistently, have somebody watch a feed before you restructure your feeding on the basis of a diaper.
If feeding is behind it
When green is a problem
Colour alone is almost never the signal. It's colour plus something else.
- Green with blood or mucus, persistently, which wants checking.
- Green and watery and much more frequent than usual, which is diarrhoea and dehydrates a small baby quickly.
- Green alongside poor weight gain or fewer wet diapers.
- Green with a baby who's distressed at feeds, arching, or has eczema and reflux, which raises the question of cow's milk protein allergy.
- Green that has persisted for weeks with a baby who isn't thriving.
- Green with a fever, and urgently in a baby under three months.
A green diaper in a cheerful, feeding, growing baby is a green diaper. Note it and carry on.
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Bamboo Swaddles (2 pc)S$49.00Shop nowShould you switch formula?
Almost certainly not, and this is where a great deal of money gets spent for nothing.
Green stool on iron-fortified formula is expected and isn't a sign it disagrees with her. Switching formulas repeatedly is one of the more common things anxious parents do, it unsettles a baby's gut each time, and it very rarely resolves anything.
Change formula when a doctor tells you to, and specifically when there's a diagnosed reason, an allergy, a reflux plan, a medical need. If you suspect cow's milk protein allergy because the crying comes with eczema, blood or mucus in the stool, reflux or poor weight gain, that's a doctor. Don't cut dairy out of your own diet unsupervised while breastfeeding, which is a long, restrictive road that usually ends without an answer. I know three people who've done it. I'm not sure any of them found anything.
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This guide is general information, written to help you understand a topic and ask better questions. It is not medical advice and does not replace your own doctor, midwife or paediatrician. Anything that worries you about your baby belongs with them.