What makes breastmilk frothy? Causes, fixes, and safety

December 21, 2025 •

5 min read

Research from Cimilre Breast Pumps indicates that pumping can naturally introduce air into milk, creating bubbles that make it appear frothy. This is a common and usually harmless occurrence, often related to the mechanics of milk expression and storage rather than an issue with the milk's quality.

Quick Summary

Frothy breastmilk can result from air incorporation during pumping, high lipase activity, a forceful letdown, or improper storage techniques. While generally safe, minimizing air intake can prevent potential baby discomfort, with solutions ranging from pump adjustments to proper handling.

Key Points

Pumping Mechanics: Incorrect pump settings, ill-fitting flanges, or loose pump parts can easily introduce air and cause breastmilk to appear frothy.
High Lipase: A natural enzyme variation can cause milk to become foamy and develop a soapy or metallic taste after storage, though it remains safe and nutritious.
Forceful Letdown: A strong flow of milk can create significant turbulence as it is expressed, resulting in noticeable froth.
Not Foremilk-Hindmilk Imbalance: While a true foremilk-hindmilk imbalance can cause green, frothy stools in a baby, it does not typically cause the milk in the bottle to appear frothy.
Handling and Storage: Vigorous shaking to mix separated milk layers or the presence of soap residue on un-rinsed pump parts can create foam.
Gas and Fussiness: Excess air consumed from frothy milk can contribute to increased gas and discomfort in some babies, making it beneficial to minimize bubbles.

Causes of Frothy Breastmilk

Experiencing frothy breastmilk can be unsettling for a new parent, but understanding the underlying reasons can provide clarity and peace of mind. While the milk's foamy appearance is almost always benign, it's helpful to know the factors at play.

Air Incorporation During Pumping

This is one of the most common reasons for frothiness, and it’s a simple mechanical issue. As a breast pump's suction and release mechanism works, it can draw air into the collection container, creating bubbles. Several factors can increase the amount of air introduced:

Ill-fitting flanges: If the flange is too large or too small, it can allow air to leak into the system, mixing with the milk.
High suction settings: A stronger suction level or a faster pumping speed can create more agitation and turbulence, leading to more foam.
Loose connections: Any loose parts within the breast pump, such as a worn-out membrane or improperly assembled components, can compromise the vacuum and pull in air.

High Lipase Activity

Breastmilk naturally contains the enzyme lipase, which helps break down fats for easier digestion. For some, this enzyme is more active than average, a condition known as high lipase. While this is not harmful to the baby, it can cause the milk to become foamy, and alter its taste and smell, giving it a soapy or metallic flavor after storage. The frothiness from high lipase typically becomes more noticeable after the milk has been refrigerated or frozen for some time, as the enzyme continues its work.

Forceful Letdown

A forceful or overactive letdown can also contribute to foamy milk. A letdown is the reflex that pushes milk from the breast. When this happens with excessive force, the milk enters the bottle quickly, creating turbulence and bubbles. This is particularly common in mothers with an oversupply of milk.

Improper Handling and Storage

Vigorous shaking: When mixing milk that has separated into fat and watery layers, shaking it too hard can create significant foam, much like shaking a bottle of regular milk.
Transferring milk: Pouring milk between containers multiple times can also introduce air and cause bubbles.
Soap residue: While rare, residual soap or detergent on improperly rinsed pump parts or bottles can react with the milk and create foam.

Potential Issues and How to Address Them

While the frothiness itself is not a safety concern, the trapped air can sometimes lead to issues for the baby. Consuming excess air can cause gas, tummy pain, and fussiness.

Foremilk-Hindmilk Imbalance

This is often mistakenly linked to frothy milk in the bottle. Foremilk (the thinner milk at the start of a feed) has a higher lactose content, and if a baby primarily receives this without enough of the fattier hindmilk, it can cause a temporary lactose overload. This leads to digestive upset, with symptoms including frothy, green, explosive stools, gas, and general discomfort, rather than simply foamy milk in the container. Block feeding or allowing the baby to empty one breast fully before switching can help correct this imbalance.

How to Minimize Frothiness

Optimize your pumping technique: Use lower, gentler suction settings on your pump to reduce turbulence. Ensure all pump parts are correctly and securely assembled to prevent air leaks.
Check flange fit: A properly sized flange is crucial for an effective and air-free pumping session. Consult a lactation professional if you are unsure of your size.
Manage forceful letdown: If you have an overactive letdown, try hand-expressing or pumping for a few moments before a feed to let the initial flow subside. You can also try laid-back or side-lying feeding positions to slow the flow.
Mix gently: When recombining the fat and watery layers of stored milk, gently swirl the container instead of shaking it to prevent creating new bubbles.
Let the milk settle: After pumping, allow the bottle to sit for a few minutes. The foam will naturally dissipate on its own.
Address high lipase: If you know you have high lipase and your baby rejects the stored milk, you can scald the milk by heating it to just below boiling and then rapidly cooling it before storing. This deactivates the enzyme. For a great resource on this process, visit Exclusive Pumping's guide to scalding milk (note: link for illustration, actual URL not provided).
Add gas drops: If frothy milk is causing your baby discomfort, adding a few safe gas drops (containing simethicone) can help break down the bubbles.

Common Causes of Frothy Breastmilk: A Comparison


Cause	Appearance in Milk	Associated Symptoms in Baby	Solutions
Pumping Mechanics	Foamy, bubbly milk, especially right after pumping.	Possible increased gas or fussiness from consuming air.	Adjust pump settings, ensure proper flange fit, check for loose connections.
High Lipase Activity	Foamy or bubbly milk after storage, accompanied by a soapy or metallic taste and smell.	May reject stored milk due to taste change. No direct harm from the lipase.	Scald milk before storing, mix gently, or add gas drops.
Forceful Letdown	Frothy milk in the bottle, baby may gulp, choke, or sputter during feeding.	Can cause gas, fussiness, and foremilk-hindmilk imbalance.	Hand express before feeding, use laid-back positioning.
Handling/Storage	Bubbly milk after vigorous shaking or transferring. Potential off smell if contaminated with soap.	Increased gas or fussiness.	Gently swirl to mix, rinse pump parts and bottles thoroughly.
Foremilk-Hindmilk Imbalance	Milk may not appear frothy in the bottle, but baby may have green, frothy stools.	Intense gas, fussiness, explosive stools, and sometimes poor weight gain.	Block feeding, allow baby to finish one breast completely.

Conclusion

Witnessing frothy breastmilk can be surprising, but it's a very normal part of the breastfeeding and pumping experience. In most cases, it's caused by simple, harmless factors like air being introduced during the pumping process or natural variations in milk composition due to lipase. The best course of action is to observe your baby's behavior and adjust your technique based on the likely cause. If the frothiness is consistently linked to digestive issues like excessive gas, a simple adjustment like letting the milk settle or adding gas drops may help. If you have persistent concerns, especially regarding foremilk-hindmilk imbalance or milk refusal, consulting a lactation consultant can provide tailored guidance and support. Remember, frothy breastmilk is not a sign that your milk is bad or less nutritious; it's simply a phenomenon that can be managed with a little knowledge and patience.

Frequently Asked Questions

Yes, in almost all cases, frothy breastmilk is perfectly safe for your baby to consume and does not indicate that the milk is spoiled. The froth is typically just air that has been incorporated into the milk.

Yes, an oversupply can lead to a forceful letdown, where milk is expressed quickly and creates turbulence and bubbles as it enters the bottle or during breastfeeding.

High lipase activity often causes milk to develop a soapy, metallic, or fishy taste and smell after being refrigerated or frozen, in addition to sometimes appearing frothy.

The extra air in frothy milk can potentially contribute to gas or fussiness in some babies. You can help reduce this by letting the milk settle after pumping or mixing it gently before feeding.

Instead of shaking vigorously, gently swirl the container to mix the separated fat layers back into the milk. This minimizes the introduction of air and agitation.

Yes, if pump parts or bottles are not rinsed thoroughly after washing, lingering soap residue can cause foaming when it comes into contact with the milk. Always ensure equipment is well-rinsed.

Frothy stools, when accompanied by fussiness and gas, can indicate a foremilk-hindmilk imbalance, also known as lactose overload. In this case, the issue is not with the milk's appearance but with the baby receiving too much of the higher-lactose foremilk.

Yes, you can let the milk sit for a few minutes to allow the bubbles to settle. Some parents also find that adding a small, safe dose of simethicone gas drops can help break down bubbles quickly.