Breastfed vs Formula Baby Poo: Colour & Smell | Parenting Hub
Breastfed and formula-fed babies have very different poos. Here's what each should look like — and what changes when you mix or switch.
Breastfed and formula-fed poos look, smell and behave differently. Neither is better — but knowing what's normal for your baby's feed helps you spot real problems.
Breastfed poo
- Mustard yellow, occasionally green
- Runny, seedy, almost like grainy yoghurt
- Mild, slightly sweet smell
- Many per day in first weeks, then can become infrequent (once every 5–10 days) and still be normal if soft
Formula-fed poo
- Tan, light brown or yellow-brown
- Thicker — peanut butter or paste consistency
- Stronger smell (closer to adult poo)
- Usually at least once a day; less frequent than this can mean constipation
Mixing breast and formula
Adding any formula usually makes poo thicker, browner and stronger smelling. This is normal — not a sign anything is wrong.
Switching formulas
Expect 5–7 days of unsettled poo (sometimes greener or looser) while baby adjusts. Persistent diarrhoea, blood or mucus warrant a GP review.
When to seek help
- Hard, dry pellets in a formula-fed baby (constipation)
- Watery, frequent diarrhoea lasting >24 hours
- Blood or persistent mucus
- Poor weight gain alongside any poo change
Common questions
Why does formula poo smell stronger?
Formula proteins are digested differently, so the by-products are more like adult-style stool. It's not a sign of a problem.
Is one type of poo healthier?
No. Both are normal. We assess feeding by weight gain, wet nappies and a settled baby — not by poo type.