The National Dairy Council stated in their May/June 2006 article "Cow's Milk Allergy Versus Lactose Intolerance":

“Milk protein allergy and lactose intolerance underlie most adverse reactions to cow’s milk and milk products. Many differences exist between these conditions, including their cause, prevalence, prognosis, clinical symptoms, diagnosis, and management.

Cow’s milk allergy is an immunologically mediated response to one or more of cow’s milk proteins. Lactose intolerance, a non-immunological reaction, is the occurrence of symptoms after persons with low levels of the enzyme lactase (lactose maldigesters) consume lactose (milk sugar) in amounts exceeding lactase’s ability to digest it.”

May/June 2006