Lactose intolerance is caused by the bodies inability to properly digest lactose, which is sugar found in milk.
It results from the small intestine being unable to 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.
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.
Symptoms of lactose intolerance are primarily gastrointestinal-related, including bloating, stomach aches, diarrhea, gas and nausea. These symptoms are somewhat similar to a dairy allergy which includes skin irritation and hives, wheezing, vomiting, diarrhea, stomach ache, runny nose, and watery eyes.
People with a milk allergy need to eliminate milk and milk products entirely from their diets.
People with lactose intolerance, on the other hand, may be able to tolerate milk and milk products to some extent. For example, most people with lactose intolerance can drink about half a glass of milk a day without suffering from a reaction. They can also typically eat a variety of milk products, including buttermilk, cheeses, fermented milk products (such as yogurt), ice cream, and lactose-free milk.
Sufferers may take lactase enzyme pills prior to consuming milk to avoid symptoms.