What Is Lipase in Breastmilk? Understanding the Soapy Smell and What to Do About It

By: Courtney Miller, RN, BSN, IBCLC

If you’ve ever opened a bottle of refrigerated or frozen breastmilk and noticed a strange, soapy, or metallic smell, you’re not alone—and you may be dealing with high lipase. In this blog post, we’ll cover what lipase is, how to know if you have high levels of it in your milk, and what to do if your baby refuses stored milk.

What Is Lipase?

Lipase is an enzyme that naturally occurs in human milk. It plays a really important role in helping your baby digest milk by breaking down fat. Sounds great, right?

Well, here’s where it gets a little tricky. The longer milk is stored—whether in the fridge or freezer—the more lipase has time to break down the fat. That breakdown process can lead to changes in the milk’s smell and taste. For some people, this results in milk that smells or tastes “soapy” or even metallic.

Why Do Some People Have High Lipase?

Some breastfeeding parents naturally have higher levels of lipase in their milk. Unfortunately, while science has identified the effects of high lipase, the cause remains unknown. Frustrating, right? Scientists—if you’re reading this—we’re all rooting for an answer soon!

How Do I Know If I Have High Lipase?

Here are a few signs that may point to high lipase in your milk:

• Your refrigerated or frozen milk smells soapy or metallic

• Your baby refuses stored milk but happily drinks freshly pumped milk

• You’ve ruled out milk spoilage or improper storage as the cause

To test for lipase, try doing a simple side-by-side sniff or taste test. Smell or taste a drop of fresh milk and compare it to a drop of stored milk. If you notice a strong difference, especially that telltale soapy scent, lipase could be the culprit.

Remember: this milk is still 100% safe to feed your baby. In fact, I personally believe I had high lipase with my son, and he never minded the taste of stored milk. If your baby does not seem to mind it - carry on!

What If My Baby Refuses Stored Milk?

If your baby is turning away from stored milk, try the following before jumping to conclusions:

1. Offer freshly pumped milk in a bottle. If your baby accepts that, but refuses stored milk, it’s likely a lipase issue—not bottle refusal.

2. Double-check your storage process. Make sure your milk is being stored properly and that pump parts are cleaned between sessions. Spoiled milk and high lipase can sometimes be confused.

3. Use fresh milk when possible. The sooner your baby drinks the milk after it’s pumped, the less time lipase has to change its taste.

   
   

How to Handle High Lipase

If you confirm high lipase and your baby refuses the milk, you still have options:

• Scald fresh milk before storing. Heat your milk to 180°F (just before boiling) right after pumping, then immediately cool it in an ice bath before storing. This inactivates the lipase enzyme.

• Mix fresh milk with stored milk. Sometimes just a splash of fresh milk is enough to “mask” the soapy taste for your baby. Experiment with different ratios to see what works.

• A few drops of non-alcoholic vanilla extract. Some parents have found that adding a few drops to stored milk helps improve the taste. This method is controversial—there’s limited research on its safety, so we recommend using it only as a last resort and only after talking with your baby’s healthcare provider.

• Donate your milk. If your baby truly won’t drink it, consider donating. Milk banks often provide milk to NICU babies who are tube-fed and won't notice the taste.

If you donate informally, just make sure the recipient knows the milk has high lipase levels so they can make an informed decision.

Final Thoughts

High lipase in breastmilk can be one of those unexpected twists in your breastfeeding journey. It’s important to remember:

• Your milk is still safe.

• You didn’t do anything wrong.

• There are workarounds to help your baby tolerate stored milk.

Breastfeeding is full of surprises—some delightful, some a little frustrating. But you’re not alone, and you’re doing an amazing job.