Milk allergy is most common among infants and is usually outgrown in adulthood. When adults react adversely to milk - from cramps, gas, and diarrhea - symptoms are often mistaken for an allergic reaction. This is actually a condition known as lactose intolerance - inherited trait caused by the body's lack of an enzyme, lactase, needed to break down lactose, the sugar in milk or milk products.
Like food allergies, intolerances are adverse reactions to food, but unlike food allergies, they don't involve the immune system. (In cases of lactose intolerance, adults may use supplemental lactace - e.g., Lactaid - or consume dairy products from which lactose has been removed. Consultations with a nutritionist may help in identifying which supplements and which products are safe to use).