Although allergic reactions can occur to virtually any food, cow's milk is one of the foods most commonly associated with allergic reactions, particularly in children. Sometimes people allergic to cow's milk can tolerate goat's milk or soy milk (which is not a dairy product).
In addition to food allergy, many people lack the enzyme lactase, which is needed to digest lactose. Another adverse reaction associated with consumption of cow's milk is constipation. Consumption of cow's milk was determined to be the cause of constipation in roughly two thirds of children with constipation.
Finally, milk intake does not appear to change the risk of fracture due to osteoporosis. Because of this, milk should not be the only source of calcium in the diet. To avoid cows treated with recombinant bovine growth hormone (rBGH), buy organic dairy products.