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Is Baby Allergic to My Milk?

Is my baby allergic to my milk?!?  This is a common subject during consults. “I was told my baby is intolerant to lactose, so now I give a lactase supplement”.  Here, we dig into the science behind that claim!

What is lactose intolerance?


Lactose intolerance is the inability to properly digest the sugar found in milk, also known as lactose, due to inadequate levels of the digestive enzyme lactase.  Lactose can be found in all mammalian milk and human milk contains even higher amounts than cow’s milk (ever taste your breast milk?  It is sweet!) [1].  Those who suffer from low lactase levels will experience digestive issues after consuming milk products [2].


What is a lactase enzyme supplement?


Products which claim to be lactose free are those made of regular milk which has an extra lactase enzyme added to “digest” the lactose for you.  This enzyme breaks lactose down into its smaller components, glucose and galactose, for absorption [3].  Similarly, over the counter supplements are available which contain the same enzyme to allow those with low levels to still properly digest lactose.  These can be found in various concentrations depending on the target audience. 


Do babies lack this enzyme?


Infant lactose intolerance is INCREDIBLY rare.  All babies are born with lactase in their intestines and as they grow into adolescences and adults the levels may decrease, eventually leading to intolerance.  There are two caveats to this: (1) premature babies may have a short period of developmental lactase deficiency or infants with severe bowel injury (such as a virus) & (2) congenital lactase deficiency at birth which is not only rare but also easy to spot because it causes diarrhea to the point of severe dehydration and weight loss immediately after birth [4].  If your baby does not fit into one of those two categories, they do not need a lactase supplement. 


Double-bind crossover trials show no difference between treatment and placebo in breath hydrogen (a method of testing for the intolerance) and mean duration of crying [5-6].  A handful of studies possibly linking enzyme to reduced colic have been funded by formula and lactase enzyme companies [7-9].  Even with the best of intentions, this is adding an unnecessary increase in a digestive enzyme of which babies have an abundance.  Unfortunately, this can cause adverse effects for some infants, such as diarrhea, and leave parents all the more confused.  


Then what is wrong with my baby?


A milk allergy is caused by a reaction to the protein in cow’s milk and is the most common infant food intolerance [10].  When ingested by a lactating mother, this protein can potentially enter her milk and cause a reaction in her infant [11].  In fact, research shows that after cow's milk ingestion some mothers have well over a dozen different types and portions of cow's milk proteins such as beta-lactaglobulin and casein.  Lactase enzyme will not help to break down these proteins for baby or mom. 




There have literally been only a few babies in the world with a true human milk intolerance.  Adverse reactions are immensely more likely to be due to a protein intolerance or allergy from dietary foods transferred to your milk.  The great news is that is a much easier fix than “allergic to breast milk”!  If you are struggling to determine your little one’s triggers, schedule a one on one consult today.


If you are avoiding dairy, it is vital that you do not use products that are only “Lactose Free” as they still contain the milk protein.  Instead, opt for dairy-free alternatives such as coconut-based products.  Similarly, if you are taking a prescription medication which contains Anhydrous Lactose (found in many birth control pills) it is likely safe to take while nursing a little with cow’s milk protein allergy. 




  1. Fusch, Gerhard, et al. "Quantification of lactose content in human and cow's milk using UPLC–tandem mass spectrometry." Journal of Chromatography B 879.31 (2011): 3759-3762.

  2. Swagerty Jr, Daniel L., Anne Walling, and Robert M. Klein. "Lactose intolerance." American family physician 65.9 (2002): 1845.

  3. Swallow, Dallas M. "Genetics of lactase persistence and lactose intolerance." Annual review of genetics 37.1 (2003): 197-219.

  4. Heyman, Melvin B. "Lactose intolerance in infants, children, and adolescents." Pediatrics 118.3 (2006): 1279-1286.

  5. Lasekan, John B., et al. "Lactose-free milk protein-based infant formula: impact on growth and gastrointestinal tolerance in infants." Clinical pediatrics 50.4 (2011): 330-337.

  6. Miller, John J., et al. "Effect of yeast lactase enzyme on" colic" in infants fed human milk." Journal of Pediatrics 117.2, I (1990): 261-263.

  7. Kanabar, D., M. Randhawa, and P. Clayton. "Improvement of symptoms in infant colic following reduction of lactose load with lactase." Journal of Human Nutrition and Dietetics 14.5 (2001): 359-363.

  8. Ahmed, Mubashir, et al. "Clinical Efficacy Of Lactase Enzyme Supplement In Infant Colic: A Randomised Controlled Trial." J. Pak. Med. Assoc 68 (2018): 1744-1747.

  9. Kearney, P. J., et al. "A trial of lactase in the management of infant colic." Journal of Human Nutrition and Dietetics 11 (1998): 281-286.

  10. Koletzko, S., et al. "Diagnostic approach and management of cow's-milk protein allergy in infants and children: ESPGHAN GI Committee practical guidelines." Journal of pediatric gastroenterology and nutrition 55.2 (2012): 221-229.

  11. Zhu, Jing, et al. "Discovery and quantification of nonhuman proteins in human milk." Journal of proteome research 18.1 (2018): 225-238.

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