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True or False:

Allergens are Present

in Breast Milk for Weeks

The standard response I have found from medical professionals to women who are starting elimination diets is that it takes two weeks for allergens to leave their breast milk.  With this advice, the infant is commonly placed on hypoallergenic formula for two weeks while the mother adjusts her diet.  This can be problematic for her supply as well as reduce the likelihood that the infant will return to breastfeeding.  Additionally, this means that once the woman has begun her allergen free diet, she cannot go back.  If it truly takes two weeks for allergens to not be found in breast milk, then there are no “cheat meals” to speak of.  Mothers cannot enjoy even a single regular cookie on the very rare occasion because it may plague their milk for weeks on end.  So, lets dig deeper into this theory by looking into the current research available. 

How is Protein Transferred to Human Milk?

Most human milk proteins are synthesized by mammary epithelial cells, transported through the secretory pathway, packaged in secretory vesicles, and released by exocytotic fusion [1].  Additional proteins are transported to the mammary gland by transcytosis from blood plasma [2].  Many nonhuman proteins transferred through this mechanism have been detected via immunoassays, including those originating from peanuts, wheat, eggs, and cow’s milk.

STUDY 1: Peanuts

In this study, 23 women ingested 50 grams of peanuts and had their breast milk collected every hour.  For the peanut proteins they were studying, the researchers found that only 11 of the 23 had detectable levels of peanut in their breast milk.  Of those 11 women, most showed peak levels in their breast milk after 1-2 hours.  The study shows that peanuts did not enter the breast milk of several women.  For those women who did test positive for peanut proteins, all but one indicated that it was no longer detectable after 8 hours [3].

STUDY 2:  Egg

Scientists gave one group of women a daily muffin containing an egg while providing an egg-free muffin to the other group.  They found that daily consumption did not result in an accumulation of egg protein in breast milk over time [4].  In other words, the egg protein would have been eliminated from the breast milk within 24 hours before the mother ingested another egg.  If the egg protein had stayed in the mother’s breast milk, there would be a concentration accumulation with each passing day.  The same lab also found that breast milk concentration of egg protein was higher after cooked egg consumption compared to raw egg.  The amount of egg consumed directly correlated with breast milk concentration which peaked within 8 hours of consumption [4]. 

STUDY 3:  Milk


Researchers found that nearly half of the lactating women studied had detectable levels of cow’s milk protein after dairy consumption.  Cow’s milk protein concentrations peaked between 4-6 hours after ingestion and then steadily decreased for those who were positive for the protein [5].


STUDY 4:  Wheat


Of 53 lactating women given 20 grams of wheat, 41 of them tested positive for gliadin.  Maximum levels were found 2-4 hours after ingestion [6].  Another study of 49 women with unrestricted diets all expressed breast milk containing gliadin.  Six of these women were put on a 3-day wheat free diet which resulted in undetectable gliadin levels [7], indicating that the 3-day period was sufficient time to clear breast milk of wheat proteins. 


These studies, as well as several others, indicate two important takeaways:


  1. Ingested proteins associated with food sensitivities do not always enter the mothers breast milk

  2. When the protein was detected in breast milk, it was typically cleared in 6-8 hours


*More research is needed to fully understand how allergen proteins both enter and leave breast milk.


  1. Franke, Werner W., et al. "Involvement of vesicle coat material in casein secretion and surface regeneration." The Journal of cell biology 69.1 (1976): 173-195.

  2. Ollivier-Bousquet, Michele. "Transferrin and prolactin transcytosis in the lactating mammary epithelial cell." Journal of mammary gland biology and neoplasia 3.3 (1998): 303-313.

  3. Vadas, Peter, et al. "Detection of peanut allergens in breast milk of lactating women." Jama 285.13 (2001): 1746-1748. 

  4. Palmer, D. J., M. S. Gold, and M. Makrides. "Effect of maternal egg consumption on breast milk ovalbumin concentration." Clinical & Experimental Allergy 38.7 (2008): 1186-1191.

  5. Kilshaw, Peter J., and Andrew J. Cant. "The passage of maternal dietary proteins into human breast milk." International Archives of Allergy and Immunology 75.1 (1984): 8-15.

  6. Troncone, R., et al. "Passage of Gliadin Into Human Breast Milk." Pediatric Research 20.7 (1986): 696.

  7. Chirdo, F. G., et al. "Presence of high levels of non-degraded gliadin in breast milk from healthy mothers." Scandinavian journal of gastroenterology 33.11 (1998): 1186-1192.