Milk allergies and lactose intolerance are not the same thing. A milk allergy is caused by a malfunctioning immune system. The immune system identifies milk proteins as harmful "invaders" and releases antibodies called immunoglobulin E (IgE) antibodies into your bloodstream. These antibodies then release histamine, which causes milk allergy symptoms [source: Mayo Clinic]. Lactose intolerance, on the other hand, is caused by your stomach's inability to properly digest lactose, which is sugar found in milk. Your small intestine doesn't produce enough of the enzyme lactase. This enzyme is essential for the proper digestion of milk and the absorption of milk nutrients. This difficulty with digestion results in lactose intolerance symptoms [source: PubMed Health].
The symptoms of milk allergies and lactose intolerance are somewhat similar. The symptoms of a milk allergy include a variety of systems including skin irritation and hives, wheezing, vomiting, diarrhea, stomach ache, runny nose, and watery eyes [source: Mayo Clinic]. Symptoms of lactose intolerance are primarily gastrointestinal-related, including bloating, stomach aches, diarrhea, gas and nausea [source: PubMed Health].
People with a milk allergy need to eliminate milk and milk products entirely from their diets. Some people, however, who only have an allergy to one milk protein called whey, may be able to eat hard cheeses [source: Mayo Clinic]. People with lactose intolerance, on the other hand, may be able to tolerate milk and milk products to some extent. Most people with lactose intolerance can drink about half a glass of milk a day without suffering from a reaction. Moreover, people with lactose intolerance can typically eat a variety of milk products, including buttermilk, cheeses, fermented milk products (such as yogurt), ice cream, and lactose-free milk. People with lactose intolerance can also take lactase enzyme pills prior to consuming milk to avoid symptoms [source: PubMed Health].