Breast milk smell

Why does my breast milk smell?

Breast milk has more than 60 components with odours, and every mother’s milk has a unique composition. That gives breast milk a range of odours that have been described in many ways, including hay-like, metallic, sweet, and fatty. Fresh breast milk has a mild smell, but that can change when it is stored. Newborns are attracted to the smell of their mother’s colostrum, the first form of milk, and at four days old they can tell the difference between their mother’s milk and another mother’s. The smell of their mother’s milk can stimulate a baby's appetite, calm them, and reduce pain when they undergo procedures.

A) Describing breast milk smell

The smell of fresh breast milk is mild and has been described as:

  • Hay-like
  • Metallic
  • Sweet
  • Fatty
  • Fishy
  • Cooked milk
  • Fruity
  • Sour
  • Earthy

Storing breast milk, particularly by freezing it, can intensify or change the smell.

B) The origin of breast milk smell

More than 60 compounds with odours have been found in breast milk, including (Loos 2018):

  • Fats that have been partially broken down
  • Amino acids, the building blocks of protein
  • Carbohydrates (pyranones and furanones)
  • Odors from the mother’s foods, medication, or supplements

C) The baby’s response to the smell of breast milk

Smell is the first sense to develop in babies and is present as early as the 28th week of pregnancy (Eidelman 2020). Smell is closely tied to emotions and memory.  A baby may be able to remember smells for up to two years after being exposed to them while breastfeeding as a newborn. These memories can in turn influence a toddler’s behaviour (Delaunay-El Allam et al. 2010).

Each mother has breast milk with a unique composition, resulting in a variety of flavours and odours. Newborn babies are attracted to the smell of their mother’s colostrum, and four-day-old babies know the difference between their mother’s milk and another mother’s (Macfarlane 1975; Marlier 1997; Marlier 1998). Even infant formula-fed babies appear to prefer the smell of human milk over infant formula (Marlier 2005).

The smell of breast milk (Loos 2018): 

  • Stimulates the baby's appetite.
  • Calms babies.
  • Reduces the pain they feel when undergoing procedures.

The smell and taste of breast milk reflect the mother’s diet and may help babies accept a wider range of solids.

References

Delaunay-El Allam M, Soussignan R, et al. Long-lasting memory for an odor acquired at the mother's breast. Dev Sci. 2010 Nov;13(6):849-63
 
Eidelman AI. The Power of the Scent of Breast Milk. Breastfeed Med. 2020 Sep 24

Loos HM, Reger D, Schaal B. The odour of human milk: Its chemical variability and detection by newborns. Physiol Behav. 2018 Nov 8. pii: S0031-9384(18)30640-1
 
Macfarlane A. Olfaction in the development of social preferences in the human neonate. Ciba Found Symp. 1975;(33):103-17
 
Marlier L, Schaal B. Familiarité et discrimination olfactive chez le nouveau-né: influence différentielle du mode d'alimentation? [Olfactory familiarity and discrimination in newborns: Differential effect of the type of feeding?]. Enfance. 1997;1:47-61
 
Marlier L, Schaal B. Human newborns prefer human milk: conspecific milk odor is attractive without postnatal exposure. Child Dev. 2005 Jan-Feb;76(1):155-68
 
Marlier L, Schaal B, Soussignan R. Neonatal responsiveness to the odor of amniotic and lacteal fluids: a test of perinatal chemosensory continuity. Child Dev. 1998 Jun;69(3):611-23