GI Health, Health/Wellness, Patient Blog | Mar 22 2022

The difference between lactose intolerance versus milk protein allergy 

Little boy with dairy allergy in kitchen

Difficulty digesting dairy can be attributed to two common culprits: lactose intolerance and milk protein allergy. But is there a difference?… Yes! Individuals suffering from lactose intolerance do not manufacture an enzyme called lactase, whereas a milk protein allergy is an abnormal immune system response to cow’s milk. The differences in dietary guidance for each of these groups comes down to safety. Let’s dig a little deeper.

Lactose intolerance 

Lactose intolerance effects quite a large portion of the global population, prevalent in 70 to 100% of east Asian populations, as well as those of West African, Jewish, Greek, and Italian descent.1 However it effects some more than others, as lactose intolerance only effects ~5% of people from Northern European descent.1

What does this mean? It means that in the diverse world in which we live, it’s likely you know someone that cannot process lactose, it may even be yourself. 

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Unlike milk protein allergy, in which the allergen is the protein component, lactose is a sugar (or the carbohydrate component) found in milk and other dairy products. When our bodies do not manufacture an enzyme called lactase, we cannot digest lactose and this causes symptoms such as abdominal pain, bloating, gas, nausea, and diarrhea.1 Think of lactase as a key that unlocks lactose, so we can break it down and use it for energy. This is how typical digestion should work, but for individuals suffering from lactose intolerance, this enzyme is missing.

There are varying degrees of lactose intolerance, and some people can tolerate small amounts of lactose in their diet. There is naturally less lactose in yogurt and cheese due to fermentation and processing, so these foods can potentially fit into a diet notwithstanding lactose intolerance (however this can be individualized), and management can be achieved by diet alterations or over-the-counter lactase supplementation.2

On the label, if a product has dry milk solids, lactose, or lactose monohydrate as an ingredient, it may cause trouble.3 Products labeled as lactose-free are generally safe.3 However, milk proteins may still be left behind. 

Milk protein allergy 

A milk protein allergy is an abnormal immune system response to cow’s milk. While affecting 2-6% of children4, unlike lactose intolerance which differs by ethnicity, milk protein allergy is less common in adults. The main proteins in cow’s milk are called casein and whey, and symptoms can include blood-streaked stool, wheezing, coughing, and vomiting to name a few.4,5 It is imperative with this diagnosis to avoid milk proteins to prevent immediate, sometimes severe illness, and possible long-term effects (such as failure to thrive in infants and kids). Foods that contain milk proteins are6:

  • Milk/buttermilk 
  • Cream 
  • Butter/margarine
  • Whey
  • Casein
  • Cheese
  • Yogurt
  • Sour cream 

Check the ingredients list on your favorite items for these milk protein allergens. 

*Pro-tip: A plant-based or vegan label does not automatically mean it is safe! The ingredients list still must be checked for casein and/or whey as milk proteins can be engineered and added*  

By: Mollie Johnson, RDN 

If you have more questions about the difference between lactose intolerance versus milk allergy, it’s always a great idea to speak with a registered dietitian. Registered dietitians are the only credentialed experts qualified to address your unique health questions.

Medline Plus. Lactose Intolerance. Available at:,%2C%20Greek%2C%20and%20Italian%20descent. 
Stourman N., Moore J. Analysis of lactase in lactose intolerance supplements. Biochem Mol Biol Educ. 2018 Nov;46(6):652-662. doi: 10.1002/bmb.21185. PMID: 30462373. Lactose intolerance: Shopping tips for lactose-intolerant people. Available at: 
Caffarelli, C., Baldi, F., Bendandi, B., Calzone, L., Marani, M., Pasquinelli, P., & EWGPAG (2010). Cow’s milk protein allergy in children: a practical guide. Italian journal of pediatrics, 36, 5. 
Davoodi, S. H., Shahbazi, R., Esmaeili, S., Sohrabvandi, S., Mortazavian, A., Jazayeri, S., & Taslimi, A. (2016). Health-Related Aspects of Milk Proteins. Iranian journal of pharmaceutical research : IJPR, 15(3), 573–591. 
Brill H. (2008). Approach to milk protein allergy in infants. Canadian family physician Medecin de famille canadien, 54(9), 1258–1264. 
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