High lipase breast milk: why stored milk smells soapy

Stored breast milk can smell or taste soapy or metallic because lipase, an enzyme in milk, starts breaking down fat after pumping. It is not harmful, and many babies don't mind. Milk that smells distinctly sour or rancid is different: don't use it.

What is high lipase milk?

Lipase is an enzyme naturally present in breast milk that breaks down fat. Lactation consultant Kelly Bonyata (KellyMom) describes parents who find that their refrigerated or frozen milk starts to smell or taste soapy, even when they followed every storage guideline. The suspected cause is an excess of lipase, which keeps breaking down milk fat after the milk is pumped. That is why people call it “high lipase milk”.

The Academy of Breastfeeding Medicine (ABM) explains that refrigerated and frozen milk often smells different from fresh milk for the same reason: lipase breaks down fat and releases fatty acids, and the smell likely comes from their oxidation.

Is high lipase milk safe?

Yes. According to KellyMom, the milk is not harmful, and if it doesn’t smell distinctly sour or rancid, it should be safe to give to your baby. ABM adds that this fat breakdown has antimicrobial effects, which help prevent microorganisms from growing in thawed, refrigerated milk.

Milk that smells sour or rancid is not a lipase question. Don’t feed it to your baby.

Will my baby drink it?

Often, yes. KellyMom notes that most babies don’t mind a mild change in taste, but the stronger the taste, the more likely a baby is to refuse it. ABM found no evidence that babies often reject stored milk because of its smell. ABM also compares it to foods like eggs, cheese and fish, which can smell unpleasant without tasting bad.

How to tell if your milk has high lipase

There is no home test with a fixed schedule in these sources. What parents notice is that fresh milk smells and tastes normal, but the same milk smells soapy or metallic after time in the fridge or freezer. If that happens and your baby refuses the stored milk, talk to a lactation consultant before changing how you store it.

What about scalding?

The two sources disagree here, so here is what each says.

KellyMom describes scalding freshly pumped milk to stop lipase before storing it:

Heat the milk to about 180°F (82°C), until you see little bubbles around the edge of the pan. Don’t bring it to a full rolling boil.
Cool it quickly and store it.
Do it as soon after pumping as you can.

KellyMom adds that scalding destroys some of the anti-infective properties of the milk and may lower some nutrients. They don’t consider that likely to matter unless all of a baby’s milk is heat-treated.

ABM advises against it: heating milk above 40°C to deactivate lipase “is not advised because this may destroy many of the immunologically active factors in human milk.”

Because the experts disagree, and scalding changes your milk, talk to a lactation consultant (IBCLC) before you start. Never use a microwave to heat breast milk (CDC).

Storing milk while you figure it out

Normal storage times still apply: up to 4 days in the fridge and about 6 months in the freezer (up to 12 is acceptable), per the CDC. See how long breast milk lasts and how to thaw breast milk.

Keep track of which bags are which

In Milkly, every bag in your stash has its own date and location, and you can add a short note to a bag, such as "scalded", so you always know which milk is which.

Tracking by bag is part of Pro, and your first week is on Pro.

See everything Milkly does

Sources

Last reviewed: 2026-10-04

This page summarizes published lactation guidance. It is not medical advice. If your baby refuses stored milk, or you're thinking about scalding, talk to a lactation consultant (IBCLC) or your pediatrician first.