Baby poop smells like vinegar

By Hannah Whittaker RD, PGDip | Nov 30, 2022

The Ultimate baby poop guide

So you open that nappy and need answers to your questions and wish you could find them. You google baby poop guide and millions of results come back. You just want to know the answer to baby poop smells like vinegar and if is this normal?

Over the first week of life your baby’s poo changed colour quite a lot. This is pretty normal.

Babies’ poo will generally change in colour and texture over the first few weeks after birth. It’s normal for it to go from a dark colour (almost black), to greenish-brown and then settle on brown, orange, or yellow, all dependent on whether your baby is breast or formula fed.

But what if you’re concerned about your baby’s poop and want to know if it’s normal for your baby poop to smell like vinegar, this is where my baby poo guide comes in to help. I answer all the questions I get asked regularly, such as;

  • Why does my baby have mucous in their poo?
  • My baby’s poop is stringy – is this normal?
  • My breastfed baby has green, frothy poop – why?
  • My baby has blood streaks in their poo should I be worried
  • Why does my baby have green poo?

And of course the most common question is should baby poop smell like vinegar?

Read on to learn about what is normal when it comes to baby poo and what may need further investigation.

The newborn baby poo guide

baby's poop smells like vinegar

Let’s start at that first poo. Meconium.

What is meconium?

Meconium is the first poo that your baby has around 24 hours after they are born and it is thick and dark in colour and very hard to remove from your babies bum!

Meconium is made up of amniotic fluid, skin cells, tiny hairs, and other particles that your baby was swallowing when they were in the womb.

If your baby has not passed meconium and its 48 hours after birth then your health team will likely investigate this further.

What’s after meconium?

After meconium usually comes a lovely rainbow of poo, changing from greenish black to orange to generally yellowy-beige! This tends to happen over the space of a week and the colour can depend on whether your baby is breastfed or formula fed.

Newborn poop frequency and how often should I change my newborns nappy?

Well, firstly this can depend on whether your baby is breast or formula fed.

A great study from 2012 looked at the pooping habits of 600 infants up to 3 months of age and found that overall breastfed babies pooped more often than formula-fed babies. They also found that over the first 3 months of life breastfed babies went from around three poos per day to once per day.

In formula or combination-fed babies, they found no change in how often they pooed.

When it comes to changing the nappy of a newborn this should be done every time they poo which will be frequently (around 10 times per day) in the early days. After this nappy changes will be between 6-8 times per day.

Baby poo guide

What is normal breastfed baby poo? – The smell, colour, texture, and how often.

  • Smell – breastfed babies poop will generally smell sweet.
  • Colour – breastfed babies poop tends to be yellow in colour.
  • Texture – can be a soft and a little runnier, but not like water! Breastfed baby poo also has a seedy texture.
  • How often – In the first few weeks breastfed babies do tend to poop more often than formula fed babies. They may poop after every feed and then miss a few days. At 6 weeks old they are likely to poop once or twice a day. 

What is normal formula fed baby poo? – The smell, colour, texture, and how often

  • Smell – formula fed babies do tend to have smellier poo than breastfed, this is completely normal.
  • Colour – formula-fed babies tend to have brown-beige coloured poop.
  • Texture – these tend to be more of a mousse texture and not as loose as a breastfed baby.
  • How often – Formula-fed babies can poop frequently in the first few days after birth and can then generally move to once per day after around 6 weeks old. 

When should I worry about baby poo? – The baby poop guide.

My baby has loose, explosive poo

If you find that your baby has loose stools, then they may have a tummy bug. Your baby’s poop will also generally be foul smelling. The question I usually get is ‘Why does my baby’s poop smell like vinegar?’. This will generally settle in a few days. If your baby has very loose, explosive stools for more than 1-2 weeks then this can be a sign of a milk allergy. Check my page here for more support if you do feel your baby has a milk allergy

I have found mucous in my babies poo

If you find stringy baby poop that contains mucous this may be worrying, however, a small amount of mucous can be completely normal.

Mucous in poop for more that 1-2 weeks could be a sign of tummy trouble or a milk allergy.

My baby is constipated

Constipation in a newborn who is formula fed is more common than in a breastfed baby. This is due to formula milk being a little thicker and more difficult to digest than breast milk. However, this doesn’t mean that a breastfed baby can’t experience constipation. You can use some techniques to help to relieve constipation such as; cycling your baby’s legs, giving them a warm bath (they always seem to poop in the bath), or doing some light tummy massage.

Constipation is diagnosed as;

  • Fewer than 3 stools per week (this doesn’t apply to exclusively breastfed babies after 6 weeks old)
  • Hard large stool
  • Rabbit dropping stools
  • Distress on stooling
  • Bleeding associated with hard stool
  • Straining
  • Previous constipation
  • Previous or current anal fissure

If your baby has 2 or more of these symptoms you should seek support from a health professional.

My babies poo is black

Black poo in the first few days of life can be normal (meconium) and sometimes poop can look darker in colour if your baby is constipated. In some rare cases, dark coloured stools can be due to a tummy problem – if you are worried then speak with your health practitioner. 

My baby has blood streaks in their poo

If you find that your young baby has blood streaks in their poop then speak with your health practitioner as it will need further investigation. It can be linked with constipation but also blood in stools can be a CMPA symptoms

In older babies who are weaning red colour in their poo may be due to the food that they have eaten.

My baby’s poo is white

White baby poo is generally very rare and if your baby has white stools then do speak with your health practitioner.

My baby is formula fed and has green poo 

A study found that of 236 babies green stools were more common in babies who were given specialised formula. This is something that I also come across regularly. Green poo in a breastfed baby can happen on occasion and generally, this is nothing to worry about, however, if your baby continues to have green poop then speak with a health professional for further advice.

My baby is breastfed and has foam in their poop

Foamy poop in a breastfed baby may be due to your baby taking too much milk too quickly (oversupply). If you think this is the reason for foamy poop in your baby then there are some techniques that you can try to help;

  • Adjusting your positioning to help to reduce a quick letdown
  • Use responsive feeding which is when you only feed when your baby asks
  • Offering more frequent feeds
  • Massaging your breasts

If you are struggling with oversupply or don’t feel that their poop is due to this then speak with a health professional.

And of course

What is that vinegar smell?

Usually a vinegar smelling poo is due to a tummy bug or if it continues longer than 1-2 weeks it may be related to digestion problems such as lactose intolerance or more commonly cows milk protein allergy. Have a look at my blog on symptoms of cows milk protein allergy for more information.

Weaning baby poop.

As you start to wean your baby it is likely their poo will change in colour, smell and texture. This is completely normal as your baby’s digestive system is getting used to processing all these new foods. Orange baby poop can be common when your baby starts weaning.

If you are concerned that your babies poo is very smelly, contains mucous, blood or is a very dark colour then I would always advise to speak to your health practitioner or send me a message.  


I hope this newborn baby poo guide has helped to reassure you and support you when it comes to your baby’s poo.

Remember – Every baby is different and this means that each baby’s poop is different. It’s important to understand what is normal for your baby. Remember babies should poop more frequent in the first few weeks of life and they will then start to get in a rhythm that is normal for them.

Poop should also be easy to pass and typically is a green, brown or yellow colour depending whether your baby is breast or formula fed. 

When they start weaning this can cause temporary constipation as their body is now having to learn to digest more solid foods. This should pass.

My key point to check;

  • Your baby is gaining weight well and following their centile line from birth
  • They are having regular wet nappies
  • They are happy and content.

If you are worried and want more support or suspect your baby has a cows milk protein allergy then get in touch . Remember to check out my Newborn poop log to track your baby’s poo – it will be a life saver. You can get it here

Hannah x

Hannah Whittaker Dietitian Bump2baby Nutrition
Expert Pregnancy & Paediatric Dietitian at | | Website | + posts

Hannah is an Expert Registered Dietitian specialising in Vegan Family Nutrition and Cows Milk Protein Allergy. 

She is a respected figure in the field of nutrition and a captivating speaker and sought after media spokesperson being featured in esteemed publications including the Sunday Times, Independent and Huffington Post.


  • Registered Dietitian
  • First Class Degree in Nutrition


  • Over 15 years experience working in the field of nutrition
  • Respected Media Spokesperson both in the UK & USA; quoted online, TV and in local and international news
  • Writer & Researcher, supporting the BDA and PEN Nutrition



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