Intolerance or allergy
Milk allergy and lactose intolerance should not be confused
There is often confusion between lactose intolerance and allergy to milk. Since the two phenomena are completely different, it would seem useful to briefly outline their characteristics :
The term intolerance refers to the total or partial absence of the enzyme (in this case the lactase) which is required to digest or to metabolize the food. The intolerance does not induce any response by the immune system.
The term allergy, on the other hand, refers to a reaction by the immune system induced by an allergen in the food, also known as trophallergen, most frequently a protein (in this case the milk proteins, the most important ones being casein, alpha-lactalbumin, beta-lacto globulin). An allergy to milk is much more serious than intolerance to lactose.