My Breast Milk Smells Sour (What Can I Do?)

  • By: Jennifer
  • Date: March 14, 2022
  • Time to read: 6 min.

If you’re breastfeeding and your expressed breast milk smells sour which may be caused by storage issues, which is allowing your fresh milk to spoil or it may be caused by excess lipase activity in your milk.

The first thing to do is to determine if you have to reorganise your breast milk storage or if you just have too much lipase in your milk. Whilst most people might immediately say the smell is down to too much lipase, a recent study found that not all sour smelling milk had too much lipase and the cause was not thoroughly cleaned and dried breast pumps, parts and storage containers! So go over storage guidelines and check that your pumps etc are thoroughly clean, dry and sterilized before use!

Lipase is not normally an issue when nursing but in stored milk or frozen milk the fat soluble nutrients can be broken down which can cause the smell. If your baby refuses your stored milk, there are a number of things you can do, which we go through below.

What Is Breastmilk Supposed To Smell Like?

Breast milk is supposed to smell like milk. However, each breast milk has a unique smell. When your child was born, you were able to recognize and be comforted by the unique smell and taste of your breast milk. It naturally changes over time depending on what you have consumed and other factors. It may have a slightly sour smell if you have too much lipase which caused particularly issues when storing human milk. The longer it is stored the more the milk fats can break down into rancid fats.

Breast milk may sometimes become tainted with a slightly undesirable taste due to medication or supplements taken by the breastfeeding mother, as well as strong deodorants, perfumes or nipple creams. Human milk can also pick up smells from other foods like garlic etc in the refrigerator or freezer, so if this is the case use baking soda or other odor neutralizer in your fridge to avoid smell/taste transfer.

Why Does My Breast Milk Smell Sour?

Thawed milk should smell the same as when you froze it, but it if has soured its not necessarily an indication it has spoiled, it can be done to too much lipase activity.

Too much lipase may cause your milk to smell off. Lipase is an enzyme that breaks down fats in your milk. If you have too much lipase, it can cause your milk to smell sour or fishy. A baby might still drink slightly sour smelling milk but might reject sour milk. Depending on how many the smell or taste of your expressed breast milk, it might not matter.

Breast milk stored in safe conditions is still safe to drink and if your baby is refusing it you can either scald milk to reduce the sour taste or smell or donate it to milk banks. The human milk banking association will always take expressed milk. Mother’s milk is liquid gold and many milk banks are crying out for it!

A soapy or sour odor is believed to be caused by the activity of an enzyme called lipase in breast milk. There are two types of lipase in breast milk: lipoprotein lipase and bile salt dependent lipase (or bile salt stimulated lipase). Lipase helps digest fats in a baby’s stomach, and lipolysis works to prevent microorganisms from growing in stored breast milk because of its antimicrobial properties.

What Can I Do To Make My Milk Smell Better?

There are a few things you can do to help make your milk smell better:

-Drink plenty of fluids to stay hydrated.

-Avoid drinking caffeine and alcohol.

-Avoid eating foods that may cause gas, such as broccoli, cabbage, and beans.

-Take probiotics to help increase the number of good bacteria in your gut.

-Express milk after feeding and store it in the fridge. The milk will smell better if it is chilled.

Some studies have indicated that a mother’s diet full of polyunsaturated fats makes lipase worsen. But also fish oil and flaxseed supplements have been suggested to increase lipase so avoid these supplements if you find you are having an issue.

What Should I Do If I Have Excess Lipase?

Firstly, you should check if your milk is high in lipase. You can do this at home with a simple ‘pump and leave’ test. Pump your milk and then let it sit for two days in the refrigerator. Smell it when you first pump, then smell it two days later and see if now smells soapy or sour like, if so, its likely you are producing milk with a high level of lipase.

Everyone produces lipase. This enzyme is normally produced in the pancreas but has also been found as part of a baby’s digestive tract development, which starts at birth and continues through adulthood; it works there to help break down fats for people no matter their age or developmental stage!

If your baby refuses this soapy smell human milk, always remember that a milk bank will accept this milk for premature babies, so never through it away!

Will High Lipase Milk Cause Issues?

High lipase milk is not harmful to a baby. However, it can cause problems with milk storage. The milk may spoil more quickly and it may have a sour smell or taste. What might happen is that your baby rejects it, but the milk itself is fine.

If you do have high lipase milk which your baby is refusing, then consider either scalding it to remove the sour smell, or read our guide to using excess milk and all the things you can do with it!

The other thing you can do is to track when the milk is changing in flavor and taste (it can be as soon as 24 hours or as late as 5 days.). Once you know the timing it will change, then you know to use up your milk before then. You can also mix older milk with fresher milk to mask the smell!

Another anecdotal suggestion is to reduce the speed and pressure of your breast pump. Some moms have reported that a fast and high pressured pump is more likely to produce high lipase milk, however this is no research done in this area.

How Can I Deactivate Lipase By Heating?

If you want to heat your milk to deactivate the lipase, you can do this by heating the milk then cooling it quickly. This is known as scalding milk. You should scald your milk when it is fresh before storing it for best affects.

Stovetop: place your milk in a small pan and heat over low heat until it reaches a temperature of 180 degrees F. Be sure to stir the milk frequently while heating it. Do not allow it to come to a boil, once you see tiny bubbles form remove it from the heat.

Then you cool it quickly over ice to reduce the temperature before refrigeration.

Do not microwave your expressed milk.

Be aware that scalding milk can mean you lose some of the nutrient levels within the milk.

Can I Freeze My Milk If It Has A Sour Smell?

Yes, you can freeze your milk if it has a sour smell. However, the milk may lose some of its flavor. Freezing the milk will not deactivate the lipase and once you thaw the milk you will still have the sour smell issue.

How Can I Prevent Chemical Oxidation In Stored Breast Milk?

You can prevent chemical oxidation in stored breast milk by freezing it as soon as possible after expression. Be sure to avoid exposing the milk to air. You can also store the milk in a container that is made specifically for frozen breast milk.

The Bottom Line On Why Fresh Breast Milk Smells Sour

If your breast milk smells or taste soapy or sour then its either spoiled (read our guide on how to tell if breast milk is bad) or you have excess lipase. First of check your storage and freezing process to check for any bacterial contamination or to check they are thoroughly cleaned and dried.

Lipase is a natural and allows the free fatty acids to be released, however if you are producing too much you can either consider changes to your diet or scald your milk (on a rolling boil) to remove the soapy taste if your baby refuses it. If you are having further issues consider talking to your lactation consultant for help, but remember never waste human milk even it is soapy tasting as your milk bank will always accept it, or you can do plenty with excess breast milk including making a diaper rash or a milk bath!