Difference Between Lactose Intolerance and Milk Allergy 

Key Difference – Lactose Intolerance vs Milk Allergy

Lactose Intolerance and Milk Allergy are two different digestive problems, often confused to be the same as they sound similar though, there is a difference between them. Lactose Intolerance is defined as the failure to digest lactose, a type of sugar found in milk and to a lesser extent in all dairy products, causing abdominal side effects. A milk allergy is a type of food allergy in which, a person develops an allergic reaction against the proteins found in the milk or dairy products. This type of allergic reaction can lead to anaphylaxis or life-threatening circulatory collapse. The key difference between these conditions is that, the Lactose Intolerance is caused by the deficiency of an enzyme called lactase that is found in the mucosal surface of the digestive system while Milk Allergy is caused by immune reaction to one or more of the ingredients of milk.

What is Lactose Intolerance?

Individuals suffering from  Lactose intolerant have very low levels of lactase, which is an enzyme that catalyzes the breakdown of lactose in the digestive system. In most cases, this causes symptoms which may include abdominal bloating or flatulence, nausea, and  vomiting or diarrhea after consuming significant amounts of lactose-containing food. These Symptoms may appear one-and-half to two hours having a meal containing milk. The severity of symptoms correlates with the lactose load of the meal and most people suffering from lactose intolerance can tolerate a minimum level of lactose in their diets without uncomfortable side effects. Patients with inflammatory bowel disease experience gastrointestinal symptoms after lactose ingestion as their intestinal mucosa containing this enzyme is already damaged.

difference between lactose intolerance and milk allergy

Some Lactose-containing Food

What is Milk Allergy?

A person who suffers from milk allergy can be reactive to one of dozens of proteins within milk. The most common one is alpha S1-casein. Alpha S1-caseins protein is structurally different between species; however, most of the commercially farmed animals produce similar protein. This explains why someone with an allergic reaction to cow’s milk suffers similar allergic reaction to sheep’s or goat’s milk too. However, they do not develop allergy to breast milk. The allergy can be caused by specific antibodies against milk proteins or sensitized lymphocytes which can induce an immune attack against milk proteins. It will give rise to the two different forms of milk allergy: Antibody-mediated allergy, and Cell-mediated allergy. The effects of antibody-mediated allergy are very fast and more harmful than a cell-mediated reaction. These allergies always arise within an hour after drinking milk, but can occasionally be delayed longer.

The primary symptoms are abdominal, skin related or respiratory relater. These can include skin rash, hives, vomiting, and gastric distress such as diarrhea, rhinitis, stomach pain, wheeze, or full-blown anaphylactic reactions.

Key Difference - Lactose Intolerance vs Milk Allergy

Capillaritis with acute hemorrhage associated with milk allergy in an infant.

What is the Difference Between Lactose Intolerance and Milk Allergy

Definition of Lactose Intolerance and Milk Allergy

Lactose Intolerance: Lactose Intolerance is the failure to digest lactose, causing abdominal side effects.

Milk Allergy: Milk allergy is a type of food allergy in whch, a person develops an allergic reaction against the proteins found in the milk or dairy products.

Cause and Symptoms of Lactose Intolerance and Milk Allergy 


Lactose Intolerance: Lactose intolerance is almost always caused by the lactase deficiency.

Milk Allergy:  Milk Allergy is caused by allergic reactions to one of the milk proteins.


Lactose Intolerance: In lactose intolerance symptoms are usually limited to the gastrointestinal system.

Milk Allergy: In milk allergy, symptoms can involve any system of the body; Bronchospasm is an example.


Lactose Intolerance: In lactose intolerance, severity of the symptoms depends on the lactose load.

Milk Allergy: In milk allergy, severity of symptoms does not depend on the antigen load or the amount of milk consumed. A Severe allergy can occur even with very small amount of milk.

Risk Factors and Prevention of Lactose Intolerance and Milk Allergy

Risk Factors

Lactose Intolerance: Lactose intolerance is common among patients who are having a disease affecting the intestinal mucosa. Even transient lactose intolerance can occur after a bout of severe gastroenteritis.

Milk Allergy: Milk allergy is common among patient with allergic diseases such as asthma and milk can be the precipitation factor of asthma in such circumstances.


Lactose intolerance: Lactose intolerance can be prevented by consuming lactose-free food.

Milk Allergy: Milk allergy can be presented by avoiding milk containing food.


Image Courtesy:
“Pccmilkjf” by Ramon FVelasquez – Own work. (CC BY-SA 3.0) via Wikimedia Commons 
“Milk Allergy” by pulmonary pathology  (CC BY-SA 2.0) via Wikimedia Commons