A metallic scent in breast milk, often described as coppery or like pennies, can be surprising, especially when the milk appears normal. This odor is a recognized phenomenon that often raises concerns about the quality or safety of stored milk. However, this change is usually due to natural biological processes or minor environmental factors, and the milk remains safe for the infant in most cases. The primary reasons for this change stem from an enzyme imbalance, the presence of trace elements, or external handling methods.
High Lipase Activity
Lipase is an enzyme naturally present in all breast milk. Its function is to break down fats into free fatty acids and glycerol, which helps the baby digest the fat content more easily and supports efficient nutrient absorption. Heightened lipase activity is the most frequent biological explanation for a metallic, soapy, or sometimes rancid smell in expressed milk.
In some mothers, the lipase enzyme is significantly more active than average, leading to a condition often termed “high lipase.” This accelerated breakdown of milk fats occurs even when the milk is stored. The free fatty acids released during this rapid process produce the noticeable change in scent and taste, which is often perceived as metallic or soapy.
This change is purely a matter of flavor and does not indicate that the milk is spoiled or nutritionally deficient. High lipase milk is completely safe and retains all its beneficial properties for the baby. The primary challenge arises when the baby refuses to drink the stored milk due to the altered taste. This issue primarily affects stored milk, as fresh milk is usually consumed before the lipase has time to significantly alter the flavor profile.
Presence of Trace Blood
A metallic odor similar to iron or pennies can be caused by trace amounts of blood in the expressed milk. The metallic scent comes from the iron content in red blood cells. While this discovery can be alarming, a small amount of blood in the milk is rarely dangerous for the baby.
The most common source of this blood is minor trauma to the mother’s nipples or milk ducts. Causes include cracked nipples, especially during the initial weeks of breastfeeding, or improper pump flange sizing or suction settings. “Pink/Rusty Pipe Syndrome” may also occur in the first few days postpartum due to increased blood flow, causing a rust-colored tint that typically resolves within a week.
If the bleeding is persistent or heavy, consult a healthcare provider or lactation consultant to address the source of the trauma. Small, transient amounts of blood-tinged milk are generally harmless, and the baby can safely consume the milk without concern.
External Storage Factors
A metallic smell can also signal environmental or chemical contamination that occurs after the milk has been expressed. This is distinct from internal biological processes. The milk’s fat content is susceptible to chemical oxidation when exposed to external factors, which changes its flavor and aroma.
One factor is the reaction of the milk with certain metals, such as using older metal containers or pump parts not designed for breast milk storage. Improper cleaning can also contribute, as soap residue or chemical sanitizers left on equipment may chemically react with the milk. Improper storage can also allow the milk to absorb strong odors from the surrounding environment, such as food in the refrigerator or freezer.
Oxidation occurs if the milk is exposed to excessive air or light, or if containers are not sealed airtight. This chemical process alters the milk’s structure and produces a metallic or rancid scent. Ensuring all storage containers are approved for breast milk and meticulously cleaned helps prevent these external factors.
Management and Safety Guidelines
Managing High Lipase Milk
If high lipase activity is identified, the most effective management strategy is scalding the milk immediately after expression. Scalding involves heating the freshly expressed milk to about 180°F (82°C)—just until small bubbles form around the edges—and then rapidly cooling it. This heat treatment deactivates the lipase enzyme, stopping the fat breakdown process before the metallic flavor can develop, allowing the milk to be safely frozen.
Addressing Trauma and Storage
For issues related to trace blood, management involves addressing the source of the trauma, such as improving the baby’s latch or adjusting the pump settings and flange size. Applying medical-grade lanolin or expressed milk to cracked nipples can promote healing. When troubleshooting storage issues, switch to BPA-free plastic or glass containers and ensure all pump parts and bottles are thoroughly rinsed of any soap residue after cleaning.
When to Discard Milk
Milk affected by high lipase or trace blood is generally safe for the baby, though refusal due to taste may occur with high lipase milk. Milk should be discarded only if it shows signs of true spoilage, such as a sour, rotten smell, visible mold, or bacterial contamination. Seek professional medical advice if the metallic smell is accompanied by persistent, heavy bleeding or if the baby consistently refuses to feed.