Peanut allergy commands the most attention in children with severe food allergy because it is very common and can be life threatening. But milk allergy is more common in infants and toddlers because early on, cow's milk is their main source of nutrition. Fortunately many children outgrow milk allergy after 3 years of age. The most common food reaction in adults is milk intolerance. In contrast to milk allergy, milk intolerance is not life threatening (especially in adults) and not associated with an immune reaction.  Allison Tsai gave a wonderful review on the differences between food allergy and food intolerance in an earlier posting on HealthCentral (See Below).

Lactose intolerance (LI) is often associated with abdominal discomfort, bloating, gas, loose stools, and sometimes diarrhea. These symptoms generally begin about 30 minutes to two hours after consuming milk-containing products. The absence of symptoms outside of the gastrointestinal tract further supports the presence of this problem. If the symptoms are eliminated by avoiding lactose, taking lactase pills or eating foods that have lactase enzyme added to them, LI is likely the problem.

It is important to understand that milk allergy and lactose intolerance are completely different in how they cause illness. Lactose intolerance results from the failure of the small intestines to break down the lactose sugar in cow's milk, to glucose and galactose. When the undigested lactose gets to the colon, resident bacteria can't break it down. This disrupts the colonic environment causing excessive gas production and increased fluid (which causes bloating). On the other hand, milk allergy is an immune reaction caused by the development of IgE antibodies to milk proteins.

IgE antibodies are Y shaped proteins and are like antennas, once positioned on the surface of mast cells. Mast cells are located just beneath the inside surface of the intestines, skin, eyes, lungs and some other tissues. When an allergy trigger (for example milk protein) comes along and contacts the IgE, a signal is sent through the membrane of the mast cell to release histamine and other mediators. These substances are responsible for the majority of early allergic symptoms (itching, swelling, hives, abdominal pain, vomiting and diarrhea).

Although LI is not associated with anaphylaxis and accordingly not life threatening, the discomfort associated with it can greatly impact the quality of life of people who have it. Avoiding dairy products can be more challenging for adults compared to children, because of the much broader appeal for various foods. A delicious steak dinner may turn into a horrible experience simply because it was doused with butter. A night out at the movies may have an unhappy ending because the artificial flavoring added to the popcorn contained milk protein.

How is Lactose Intolerance Treated?

 As with any other food allergy or intolerance, once the culprit is identified you avoid it. The problem is dairy products are very widely used in processed foods, sauces, gravies, dressings and many recipes, so avoidance is really not easy.