If you’re pumping and storing milk, you might notice that sometimes your milk smells a little… off. It can be confusing and even a little upsetting, especially when you’re doing everything “right” and still getting a soapy or metallic smell after refrigerating or freezing your expressed milk.

This is more common than many people realize, and it does not mean your milk is bad or that your body is doing something wrong. What you’re noticing is usually a natural variation in something called lipase. This guide will help you understand the effects of lipase, why it happens, and—most importantly—what you can do to feel confident moving forward.

What is Lipase?

Lipase is a natural enzyme that helps break down fat in breast milk so your baby can digest it easily. Think of it like a tiny helper that keeps the fat mixed into the milk, so your baby gets all those essential nutrients. So yes—lipase is a good thing. It’s one of the numerous reasons breast milk is so special.

For some moms, lipase activity is higher, and the milk can start to change in smell or taste once it’s stored. High lipase breast milk is still safe, still nutritious, and still “liquid gold.” High levels of lipase do not reduce the nutritional content of the breast milk your are providing for your baby or take away its protective benefits.

What Causes High Lipase in Breast Milk?

There isn’t a single clear cause of breast milk developing high lipase activity. This is usually an individual case, based on natural differences in how each person’s body produces milk. Some moms simply have milk with higher lipase activity. This means the fat in the milk begins breaking down sooner, especially once the milk is expressed and stored.

It’s important to remember:

  • This is normal

  • It’s not related to diet or hygiene

  • It’s not something you caused

It’s just part of the natural variation in milk composition and does not alter its nutritional value.

Signs of High Lipase Content

  • Milk develops a soapy, metallic, or sour smell or flavor

  • Milk smells sour or “off” after refrigeration or freezing

  • Milk looks completely normal but smells or tastes different

  • Baby may refuse stored milk, but drinks fresh milk easily

Why Does Stored Milk Smell Different?

When milk is stored, lipase can break down fats and release fatty acids, which may lower the pH of the milk. The odor of your milk likely comes from the oxidation of these fatty acids that can create an “off” or unpleasant smell. This doesn’t mean the milk is spoiled. In fact, the good news is that this process actually provides an antimicrobial effect that helps protect your expressed milk from unhealthy bacteria. That’s one of the remarkable biological qualities of the milk itself.

Even when the smell of the milk is unpleasant, the milk is still safe—it just may not be appealing to every baby.

How to Manage High Lipase Milk

If you suspect high lipase milk, here are some helpful tips you can try. You may find that a different approach works better for you depending on your routine and storage needs.

Milk Collection

After pumping, try putting your milk container in an ice bath right after pumping and freezing your milk as soon as possible. This can help slow lipase activity early on and reduce the chance of the milk developing that soapy smell later. Some parents notice this change in smell even after a short time in the refrigerator or freezer. In other cases, it takes a longer time for the stored milk to develop this smell.

Milk Storage

Make sure that you are storing your milk according to recommended guidelines. Milk stored in different environments (deep freezer vs. fridge freezer) may smell different.

  • Store milk in the coldest part of your freezer

  • Freeze milk as soon as possible after pumping

  • Avoid temperature fluctuations (like putting milk in the freezer door)

While freezing slows but does not stop the lipase from breaking down the fat in the milk, using a colder setting helps slow fat breakdown and may reduce odor changes. The goal here is to keep milk as cold as possible.

What if My Baby Refuses Stored Milk?

While most babies accept stored milk without issue, some—particularly young babies—are more sensitive to subtle changes in flavor or smell. This doesn’t mean something is wrong with your milk or that feedings will continue to be difficult. In many cases, simple adjustments can help your baby accept milk more comfortably:

Using Fresh Milk

If your baby refuses stored milk, the most effective solution is often to use fresh milk whenever possible. Fresh milk, stored at room temperature and fed within 4 hours, typically does not have the altered, unpleasant taste or smell that stored milk can develop.

Mixing Milk

If you need to use stored milk, try mixing it with freshly expressed milk. This can dilute the soapy or metallic taste of the milk and make it more acceptable for your baby. It may take some experimenting to find a ratio that your baby will accept.

Avoid Heating Milk

Some people suggest heating or scalding milk to deactivate lipase, but The Academy of Breastfeeding Medicine does not recommend heating milk above 40°C (104°F). Heating milk can damage important immunological factors and nutritional components in breast milk.

What Else Could it Be?

Sometimes the scent of breast milk is off for reasons that aren’t related to lipase enzyme. Potential culprits include:

  • Pump parts that weren’t cleaned thoroughly

  • Milk stored for too long of a period of time

  • Milk exposed to heat or temperature changes

If your baby is refusing milk, it’s worth checking these possibilities too.

When to Reach Out

If you’re feeling unsure or overwhelmed, it’s totally okay to ask for help. A lactation consultant can:

  • confirm whether it’s high lipase milk

  • talk through storage options that fit your routine

  • help you understand what’s normal for your individual case

  • support you in protecting both milk supply and confidence

The Takeaway

High lipase milk is normal, safe, and still packed with everything your baby needs. A different smell doesn’t change the value of your milk—or the care you’re giving your baby. Many families go through this, and there are plenty of ways to work around it. If you’re feeling stuck, reach out—support can make a big difference. You’re not alone, and you’re doing the best for your baby.

Disclaimer: Our classes and accompanying materials are intended for general education purposes and should not replace medical advice. For personalized recommendations, please consult your healthcare provider and/or lactation consultant.