Breast Milk Smells Like Vinegar – Is This Normal? 

breast milk smells like vinegar

If you’re a nursing mom, you’re dealing with breast milk every day. Whether this is your first time, or you are an experienced breast feeder, changes in the smell of your breast milk may come as a big surprise. Undoubtedly, most moms are rather concerned if they find their breast milk smells like vinegar.

The first time you’ve smelled that your breast milk is sour after pumping it out, you may have assumed that it has somehow gone off or spoiled. This can be an unpleasant surprise, especially if you didn’t actually leave your milk in the bottle for too long. 

So, if your breast milk smells like vinegar, should you be worried? Here’s everything you need to know!

What You Need to Know about Breast Milk

Breast milk is the fluid produced by women’s mammary glands and stored in breasts. During breastfeeding, it flows through the nipples. In fact, the primary role of female breasts is for the purpose of breastfeeding.

Women go through many changes in pregnancy due to hormonal alterations. One such change is the initiation of breast milk production. This is done thanks to the hormone oxytocin that the body produces during pregnancy.

Another important hormone is prolactin. Prolactin causes your breast milk to flow. It often needs to be stimulated, and this is done when your baby sucks on your nipple. This will trigger the flow of the breast milk. So you’ll be wondering now why your breast milk smells like vinegar?

Breast Milk Smells Like Vinegar – Causes of Sour Smell

The smell of breast milk is caused by the enzyme Lipase. Enzymes are biological catalysts that speed up metabolic reactions in your body. All enzymes are specific, meaning that they’ll react with only certain substances. 

Lipase is the enzyme that speeds up digestion. It helps your body breakdown fats into their component molecules – fatty acids and glycerol molecules. Lipase is found naturally in breast milk as it helps break down breast milk fats. This makes it easier for your baby to digest the milk. 

However, sometimes you may produce more lipase than normal. 

If your breast milk smells like vinegar, this is caused by excessive lipase production that gives it a sour smell. 

If this happens to you, don’t panic! Lipase is safe for your child. They can still consume your milk without any problems as it won’t harm their health. So, if you’ve previously tasted your milk and already know the answer to ‘what does breast milk taste like ?’ and you’ve all of a sudden noticed it tasting more sour than usual, this is likely caused by increases in lipase levels. The same goes for the soapy feel of milk. 

Still, some babies are picky eaters. They are sensitive to smell and taste, and this can make them reject the more sour smelling milk. Most babies, however, don’t really mind. As long as your little one is comfortable drinking it, they will be fine. Don’t worry.

Can You Prevent Excessive Lipase Production?

There are many reasons why you may produce more lipase than normal. As mentioned before, this shouldn’t concern you as long as your child is willing to consume your milk. However, if your little one refuses to eat, then it’s time to take some measures to lower your lipase levels. 

Here are a few things you can do:

Test It before Freezing

Some women, especially if they produce a lot, prefer to pump and then freeze their breast milk. In this case, try tasting it beforehand to see if there are any changes in the taste. If it tastes sour, it’s likely to have a higher lipase content, and this will be rather more noticeable in just a few hours. Make sure to observe its color and smell, as well.

If it tastes normal, you can safely freeze your milk. However, if it seems more sour than usual, even just a little bit, then the chances are it’ll smell much worse once you take it out of the freezer. 

It’s also a good idea to start freezing your milk in small quantities initially. Defrosting the smaller amounts at different time periods of being frozen, will allow you to work out how long you can freeze it without before it gains the sour taste. Then you can start freeing in larger volumes. Remember, once you thaw frozen milk, you can not refreeze it!

Scald Fresh Milk

So if you’re noticing the milk is changing taste after freezing, then it’s likely your lipase levels are high. Whilst there is no way of changing the milk that has already been frozen, you can better prepare your freshly produced milk ready for freezing. One option is to scald your fresh milk.

Here’s how to scald your fresh milk before putting it in the freezer:

  • Put your breast milk in the pot. 
  • Apply heat (approximately 180 degrees F) and wait until you see tiny bubbles forming on the edges of the pan.
  • Don’t allow your milk to boil!
  • Once your milk has been scalded, allow it to cool down before you put it in a freezer.

Scalding is an effective method to prevent your milk from turning sour. This is because it prevents the lipase from breaking down the milk. 

Keep in mind that scalding will take away many benefits breastfeeding has for the baby. As such, it should be done as seldom as possible. 

Can Other Things Cause Your Breast Milk to Smell Bad?

If your breast milk smells like vinegar, then high levels of lipase are the likely cause. However, this isn’t the only unusual breast milk smell moms complain about. Changes in smell can be caused by a variety of factors. Some are much more worrisome than a simple fluctuation of enzyme level. 

Here are some factors that can cause your milk to change how it smells: 


There are some foods that make breast milk taste bad. Research has proven that a mother’s diet can have a huge influence on the taste of milk. 

For example, strongly flavored foods, such as chili, soy sauce and garlic, can change the taste of the breast milk. You know how they say that you can smell someone who has eaten garlic even a few days later? The same may apply to the taste of your breast milk if you’ve eaten foods like these. 

While most of these things won’t make your milk harmful, these changes in taste can be off putting for your baby. As such, if you’re planning on changing your diet and adding something new in, it’s best to start it slowly. 

Keep in mind there’s probably a good chance your baby is already used to the food you regularly eat, or at least what you used to eat during pregnancy. This is one of the reasons why you should be careful about what you eat during pregnancy, and not just during breastfeeding.


Certain medications can also change the taste of your breast milk. If you’ve started taking some medicine and you notice your little one will no longer take breast milk, then it may well be that the new drugs have changed its taste. 

Most medicines will come with a list of common side effects. Some of these are important to note if you are breastfeeding. So, it’s essential to talk to your doctor before starting any type of therapy. When consulting with your doctor, ask them if your breast milk will be affected. Some medicines taken by mom can actually work their way into their breast milk, so great care has to be taken. You don’t want your baby to ingest medicines they don’t need and are not designed for them.


There are many reasons why you shouldn’t smoke while breastfeeding. When you smoke, dangerous chemicals will be transmitted to your nursing baby. This causes significant harm to your little one even if they aren’t in the same room, or close to you while you smoke. 

Smoking can also reduce the volume of breast milk, greatly affecting your child’s important supply of natural nourishment. Some moms who smoke may even stop producing milk altogether. Smoking reduces the release of oxytocin and prolactin which are important hormones in breast milk production, as mentioned above. 

Not just that, but smoking will likely change the taste of your milk. Even if you didn’t smoke during pregnancy but restarted your bad habit after giving birth, your child will eventually start noticing the changes in taste. Most of the time, this will make them refuse to want to breastfeed anymore. 

Storage Techniques

It is recommended you give breast milk to the baby as fresh as possible. Of course, this isn’t always possible.

How you store your pumped breastmilk is very important. If you do it incorrectly, it will affect not just the smell, but also the taste and appearance of the milk. 

If you’ve ever left a bottle of milk at room temperature for a few hours, you’ve likely noticed your milk separating into layers. You’ll notice a creamy, white layer floating on top, whilst the bottom will look more watery. 

The same can happen if you store your bottle in a refrigerator, especially if it is held here for longer than recommended.

You can try to swirl the bottle around a bit and try to mix both layers together. However, your milk will likely still taste sour. Your best option is to store the milk at the correct temperature for no longer than the recommended time frame. This will ensure it stays tasty for as long as possible. 


While freezing is a great way to store your breast milk, a lot of moms report that it can have a negative impact on the smell. This can occur even if you don’t have excess lipase. The whole freezing and thawing process can give your milk an unpleasant smell. This will also affect the taste. 


Finally, research has shown that stress and anxiety can affect not just the production of the breast milk, but also its taste. This is because stress results in an increase of adrenaline, which can not only hinder the milk ejection reflex, but also influence the production of enzymes such as lipase. 

This is quite common in first-time moms, who may be more overwhelmed and prone to stress after giving birth.  

What Does Breast Milk Smell Like when Spoiled?

Now you know that when your breast milk smells like vinegar, it doesn’t necessarily mean that the milk is spoiled. However, how will you know your milk is no longer good? 

Breast milk, just like cow’s milk, will spoil in time if you leave it at room temperature, or even in the refrigerator. This is one of the reasons many mothers switch to formula. Overall, breast milk should be stored in a refrigerator for no longer than four days. Of course, if you put it in a freezer, it can last much longer – even up to a year in certain circumstances. Once you thaw it, though, you have to use it as quickly as possible – normally within 24 hours.

But how can you tell that your breast milk smells bad because it’s spoiled, and not due to something you ate or lipase? There are a few tell-tale signs are: 

  • It will smell really foul – and we’re not talking just vinegar-like smell. It will have a smell that will strongly resemble the smell of a rotten cow’s milk. Beware, though, that sometimes milk can smell foul while still being fresh. And that some people have a lot more of a sensitive nose than others.
  • The layers don’t milk when swirled. Many new moms mistake breast milk separation for souring. Look for chunks in the milk that won’t swirl. If they exist, the milk has gone off. The same goes for when your milk won’t mix at all. 
  • It was in the fridge for longer than four days. Don’t even bother trying it and throw it out. It’s better to be safe than sorry.
  • You didn’t store it properly. A breast milk pouch that hasn’t been properly sealed or if you’ve kept it outside of the fridge will spoil rather quickly. If you notice any of the signs we mentioned, this is a clear indication that the milk is spoiled. 


If your breast milk smells like vinegar even though you know you’ve stored it properly, don’t panic. This doesn’t necessarily mean that the milk is spoiled or that it’ll harm your baby. This is likely just the sign of excessive lipase production that’s causing the smell and taste of the milk to change. 

If your child doesn’t mind drinking milk that tastes sour, then there is no reason why you shouldn’t give it to them. However, if they are put off feeding on the milk due to the taste of the food they consume, don’t force them. Try some of the steps we’ve mentioned. You always have formula milk as a safety net to fall back on.

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