Breast milk with a strong smell

Why does my breast milk smell funny after thawing?

Breast milk may develop a strong smell after refrigeration or thawing. The smell has been described as metallic, fishy, rancid, or sweaty. One possible cause is an enzyme in breast milk called lipase. The enzyme causes changes in milk fat. The smelly milk is still good, but some babies refuse to drink it. To prevent the smell, mothers can scald the milk. This is done by heating the milk in a water bath to 62°C (145°F) for one minute or for 80°C (180°F) for 15 seconds. It is then cooled quickly and place in appropriate storage containers. 

A) Changes in the smell of stored breast milk

Freshly expressed breast milk has a very mild smell (Loos 2019).

Storing breast milk in the refrigerator can give it a more intense smell that has been described as sweaty or rancid.  

After freezing and thawing, it can smell even stronger. The smell has been described as metallic, fishy, rancid, or sweaty (Spitzer 2010a). In general, the longer milk is frozen, the stronger the smell can be (Hung 2018).

It may be that the difference in smell results from changes in breast milk fat caused by enzymes (lipase) in breast milk (Spitzer 2010b). Other possible causes of the stronger smell include (Pitino 2019):

  • The number and types of bacteria present
  • Changes in milk fat caused by storage
  • Increasing levels of acid
  • The mother’s diet or her use of supplements

B) Problems caused by breast milk with a strong smell

Breast milk that has been expressed and properly stored  but has a strong smell is perfectly good to use (Pitino 2019). However, some babies won’t drink it, which becomes a problem.  

In one small study, one-quarter of the mothers surveyed noticed an “off” smell in their expressed and stored milk and nearly all of their babies refused the milk (Francis 2018).

C) Preventing the smell

Breast milk can be heated without boiling (scalded) to prevent the smell from developing. This is best done as soon as possible after expressing to keep the milk from acquiring the smell. Once present, it cannot be removed.

To scald breast milk:

  1. Express and collect the milk in a glass jar.
  2. Place the jar in a cooking pot.
  3. Pour water into the pot to surround the jar (a water bath) but keep the level of the water slightly below the level of the milk to prevent the jar from tipping.
  4. Heat the pot on a stove until:
    1. Small bubbles form at the edge of the pot and; 
    2. The milk is at 62°C (145°F) for one minute, or the milk is at 80°C (180°F) for 15 seconds.
  5. Cool the milk quickly by placing the jar in an ice bath (a bowl of water and ice).
  6. Place the breast milk in appropriate storage containers.

Milk temperatures can be measured using a candy thermometer.

Milk will quickly run over if it is boiled. This can be messy and may result in burns to mothers or others in the household. It is best to remain close by any milk on the stove.


Frances J, Dickton D. Feeding and refusal of expressed and stored human (FRESH) milk study - a short communication. J Nutr Health Food Eng. 2018;8(6):391‒393
Hung HY, Hsu YY, Su PF, et al. Variations in the rancid-flavor compounds of human breastmilk under general frozen-storage conditions. BMC Pediatr. 2018 Mar 2;18(1):94
Loos M, Reger H, Schaal D. The odour of human milk: Its chemical variability and detection by newborns. Physiology & Behavior. 2019;199:88-99
Pitino MA, Stone D, O'Connor DL, et al. Is Frozen Human Milk That Is Refused by Mother's Own Infant Suitable for Human Milk Bank Donation? Breastfeed Med. 2019 Feb 21
Spitzer J, Buettner A. (Spitzer 2010a). Characterization of aroma changes in human milk during storage at −19 °C. Food Chemistry. 2010;120(1):240-46
Spitzer J, Doucet S, Buettner A. (Spitzer 2010b). The influence of storage conditions on flavour changes in human milk. Food Quality and Preference. 2010;21(8):998-1007