Formula-fed baby poo versus breastfed baby poo: what’s the difference?

Your baby’s poo can look very different depending on how they’re fed. Babies who are breastfed tend to produce different consistencies and frequencies of poo, compared to formula-fed babies or babies fed a combination of both.

Your baby’s first poo will often be sticky and greenish black in colour, regardless of whether they’re breastfed or formula-fed. After a few days, the appearance of their poo should change to a yellow or mustard colour. The colour, shape and frequency of their poos will likely change regularly throughout the following couple of months.

Research continues to support the choice to breastfeed infants wherever possible, as breast milk provides the most optimal source of nutrition for babies. However, breastfeeding is not always available for parents, with factors such as comfort, lifestyle and medical conditions impacting this decision.

Breast milk provides an easily digested source of nutrition for infants, supplying lactose, protein and fat, as well as many of the vitamins and minderals a newborn needs. This means that breastfed babies have fewer digestive complications than formula-fed infants on average, also resulting in fewer instances of diarrhoea and constipation.

Breastfed babies usually produce softer, runnier poo which generally smells less offensive than formula-fed babies’ - in some cases it may even smell sweet.

There can be a lot of variety in what is classified as a “normal”-looking poo in breastfed infants. A mother’s diet and any medications she’s using can affect the appearance of her baby’s poo.

A "normal” poo can range in colour, from yellow to greeny-gold or brown. Most of the time breastfed baby poo is fairly runny, with a similar consistency from pumpkin soup to toothpaste. Remember, while your baby’s poo may appear quite runny, diarrhoea is rare in breastfed infants and may turn their poo green, with mucus present and  a foul smell.  Similarly, breastfed babies don't often experience constipation, and their poos should remain soft.

If your breastfed baby's poo becomes hard, pebbly or well-formed, this may be a signal that they need more breastmilk or are dehydrated. Try to feed them more frequently and check in with a healthcare professional.

Breastfed babies tend to poo more frequently than formula-fed infants during their first two months of life, with their stools being a more liquid consistency throughout the first three months. More than a quarter of breastfed infants experience infrequent poos, with this often being no cause for concern.

If your baby is formula-fed, their poo will likely be firmer, darker brown in colour, and smellier than a breastfed baby’s. Some formulas can also make your baby’s poo appear dark green in colour, which is normally nothing to be immediately concerned about.

If you make the transition from breastfeeding to formula, you’ll notice your baby’s poo becomes darker and more paste-like in texture, but it should still resemble anything from the consistency of pumpkin soup, through to toothpaste.

The frequency of formula-fed baby poos can range from several times per day, to once every few days. In their first few days of life, your baby will likely poo once or twice daily, increasing to many times per day after the first week. Some newborns poo after each feed for the first month of their life, but this often reduces after about 6 weeks. Around this time, your baby may produce several poos daily or they might go days between poos. Most commonly, they’ll have one to three  poos daily with an occasional day or so between. Each baby’s pooing habits are individual, so getting to know what’s “normal” for your baby can help you identify any abnormalities or changes in their poos.

While breastfed baby poo ranges in colour , formula-fed baby poo is generally a shade of brown, including yellow-brown, tan and green-brown. The consistency of your formula-fed baby’s poo should resemble that of peanut butter and is likely to smell more strongly than a breastfed baby’s. Formula-fed infants may also experience more gas and digestive discomfort, including constipation, compared to breastfed babies.

If you’re concerned your baby may be constipated, learn more about the symptoms here.

Babies can produce various shades of green-coloured poos for a few reasons.

If your breastfed baby produces bright, frothy green poo, this may be an indication lactose overload, making your baby gassy, hard to settle, or upset. You may notice your baby producing much more poo and wee than they normally do in a day. If you're concerned, speak to a lactation consultant or midwife.

If you notice dark green poo from your formula-fed baby, this is often due to the transit time of the formula in their gut and is usually not a cause for concern if temporary. However, if you're at all concerned, or your baby's poo continues to be green, speak to your doctor right away.

Unsure whether your baby’s poos are healthy – regardless of whether they’re breastfed or formula-fed? Our new Poo Tracker Tool can help you learn more about their pooing habits. Using our intelligent, AI-driven system which draws from an extensive library of poo examples. Our App matches a photo of your baby’s nappy taken in real-time with the most closely resembling sample in our database, helping you understand more about your baby’s poo so you can consult with a healthcare professional for guidance.