Sour Smelling Breast Milk

Your milk is liquid gold for your baby. Every bit of effort you put into keeping it safe and nutritious is totally worth it.

breast milk in a bottle
breast milk bottles
Sour Smelling Breast Milk - Audio

Ever wonder why your pumped breast milk smells a bit funky sometimes? This can happen due to various reasons. But don't fret, there are fixes for these issues too!

Pumping and storing milk is a total game-changer for many new moms. But sometimes, you may notice that your milk smells a bit off. The smell could vary, ranging from soapy or metallic to fishy, sour, or even rancid. Your little one might not care and gulp it down, but other times, they may refuse to drink your milk. And if it's truly spoiled, we definitely don't want them drinking it.

Why Does My Breast Milk Smell Sour?

There are a bunch of reasons why your milk might smell or taste a bit off, and each one has its own solution.


Did you clean your pump parts well enough after pumping? If not, some bacteria might be to blame for that weird smell in your milk. Check out how you're handling and storing your milk, and take a look at the CDC's cleaning instructions to make sure your milk is bacteria-free.

You also need to ensure that you don't leave your breast milk out too long.

Lipase Activity

Lipase is an enzyme in milk that breaks down fats so your baby can digest them. But if you have too much lipase, it can give your stored milk a soapy or fishy smell/taste. Don't worry, your milk is still safe to drink. But if your baby refuses it, try mixing it with some fresh milk. To stop this from happening again, try scalding (heating it until it's just about to boil, then cooling it fast) your milk before storing it.

For scalding milk:

Raise the temperature of the milk to around 180 F (82 C) or until you observe tiny bubbles forming around the pan's perimeter (avoid bringing it to a vigorous, rolling boil). Immediately cool the milk down and store it properly.

scalding breast milk
Scalding Milk

Chemical oxidation

If your breast milk smells sour or rancid, it might be because of chemical reactions from your diet or drinking water.

Things to avoid in your diet to prevent Chemical Oxidation

  • Ditch stuff like fish oil or flaxseed supplements, anchovies, old vegetable oils (you can tell they're off if they smell or taste funky), and certain nuts - watch out, especially for Brazil nuts, as they go rancid pretty quickly.
  • Trade your tap water for bottled water.
  • Eat more antioxidant-rich foods. Think about adding some beta-carotene and vitamin E to your diet.

If milk gets chemically oxidized, it's gone bad, and it has to be thrown out. Heating it will only make it worse. But don't stress, if you follow these diet tips above, you should be able to alleviate the problem entirely.

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Figuring Out the Problem

How can you tell if it's lipase or oxidation that's messing with your milk? First, make sure your pump is squeaky clean. Then, smell and taste your milk right after you pump it. If your breast milk smells sour, you might be dealing with rancid fats and chemical oxidation. Changing your diet can help fix this.

But if your breast milk smells fine and tastes slightly sweet, keep it in the fridge and check it every few hours. If it starts to smell or taste soapy, fishy, or metallic after some time, then lipase is likely your culprit. Follow the steps for scalding your milk to deactivate the lipase and prevent future changes.

Your milk is liquid gold for your baby. Every bit of effort you put into keeping it safe and nutritious is totally worth it.

Don't let the hiccups with breast milk storage throw you off your breastfeeding game. Keep on trucking—you've totally got this!


Milk issues - soapy, metallic, sour, or spoiled milk?