Moo Blues: Is It Lactose Intolerance Or Is It A Milk Allergy?

By: Stephanie Masiello, Cornell University PhD Candidate & IFIC FDN Sylvia Rowe Intern  Date: 7/15/13

As a student in Food Science with a focus on dairy, people love discussing their food perks and quirks with me. Often, I hear people wonder whether they are lactose intolerant due to GI issues experienced when eating dairy products, but they are not sure. Ever the scientist, I usually respond to their question with a question: "Are you lactose intolerant or are you allergic to milk?" There's really a significant distinction between them, so read on to better understand lactose intolerance and milk allergy. It's important to know the difference, to understand a bit of the science, and to know the health resources available.  

Lactose Intolerance

If someone is lactose intolerant, this means that they have a lessened ability or are incapable of digesting lactose due to a lactase deficiency. Lactose, a sugar found in milk, is not in an absorbable form for our bodies and therefore must be broken down by a specific enzyme called lactase (a little confusing, but "-ose" ending = sugar and the "-ase" ending = enzyme). Lactase is produced by cells on your intestinal villi inside your gut. The lactase released from these cells cleaves (or separates) the lactose into two simple sugars that are able to be absorbed and used by your body: glucose and galactose.

If you don't have the enzyme to breakdown the lactose into simple sugars, then the lactose ends up being fermented by the bacteria that live in your gut and colon. This fermentation results in the production of gases and leads to the all too familiar symptoms of gastrointestinal distress (bloating, cramps, and diarrhea) felt by those who are lactose intolerant.  

Milk Allergy

A milk allergy is not caused by a deficiency like lactose intolerance, but instead is a result of an overreaction from your immune system where your body is specifically responding to the presence of milk protein (casein or whey). Basically, your immune system targets the food protein, mistaking it for a threat to your body.  

If someone has a milk allergy, the IgE immunoglobulin antibodies, made by the immune system to specifically recognize the allergen (in this case, the milk protein), identify the presence of milk protein and then attach to immune cells that reside in your nose, throat, lungs, skin, GI tract, blood, and even tissues. The binding (or joining) of the IgE and the immune cell tells the immune system to release large amounts of chemicals from your body (i.e. histamine) to combat the presence of the allergen. These chemicals cause the mild to severe symptoms allergy sufferers feel, including itchiness, GI distress, skin reactions, and trouble breathing.  


If someone thinks that they are either lactose intolerant or allergic to milk, it is important to visit a physician and/or allergist for an official diagnosis and to develop a management or treatment plan.  

There are 3 tests commonly used to help diagnose lactose intolerance (after the ingestion of a high-lactose solution during a visit to a health professional):

  1. Blood test - blood is measured for glucose levels. Since glucose is one of the products from cleaving lactose, a noticeable lack of increased glucose levels may indicate lactose intolerance.
  2. Hydrogen breath test - there are normally low levels of hydrogen in the human breath. However, if your body does not digest lactose, the fermentation in the gut produces increased amounts of gas. Therefore, abnormal hydrogen levels excreted through breath may indicate lactose intolerance.
  3. Stool acidity test - the fermenting of undigested lactose actually causes an increase in lactic acid and other acids in your GI tract. An increased level of acidity may be detected in a stool sample and could indicate lactose intolerance.  

There are 2 tests commonly used by health professionals to help diagnose a milk allergy:

  1. Skin test - skin (usually on the forearm) is pricked with a small amount of milk protein. After a set amount of time, a health professional will look at the pricked area to check for the presence of a rash or hives and the degree of reaction severity.
  2. Blood test - blood is measured for IgE antibody levels post milk protein exposure. An increase in this antibody would indicate a possible milk allergy.  

Consumer Options

While there are over-the-counter medicine options (such as Lactaid)  for those who are lactose intolerant and still want to enjoy some dairy products, there are also some lower-lactose dairy foods such as certain cultured dairy products (i.e. kefir, yogurt) and hard cheeses.  

For those with a milk allergy, elimination of dairy is the commonly recommended treatment by doctors. However, the level of allergy severity will dictate whether all products containing dairy (including in baked goods) or a certain group of dairy products should be avoided. Per the US Food Allergen Labeling and Consumer Protection Act of 2004, food products containing milk, whey, or casein as ingredients should be labeled on the package. 

However, everyone's body is different and it is extremely important to work with a health professional to discuss your diet. While a general physician or allergist can give great guidance, a registered dietitian (RD) or registered dietitian nutritionist (RDN) can make sure that your daily diet is still balanced so that you don't miss out on necessary nutrients due to food restrictions.  

For more information, talk to a health professional about any lactose intolerance or milk allergy concerns and check out some of these helpful links from the National Institute of Health (NIH):