The National Institute of Child Health and Human Development wrote in their Jan. 2006 publication "Lactose Intolerance: Information for Health Care Providers":
"Individuals with lactose intolerance are unable to digest significant amounts of lactose due to an inadequate amount of the enzyme lactase.
Clinical symptoms of lactose intolerance can include abdominal pain, diarrhea, flatulence, and bloating. The severity of symptoms differs, often depending on the amount of lactase remaining in the body and how much lactose has been consumed.
Some patients with lactose intolerance may believe they are allergic to milk or milk products. A milk allergy, however, is related to the proteins in milk rather than the lactose."
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."
The National Institute of Diabetes and Digestive and Kidney Diseases wrote in their Mar. 2006 publication "Lactose Intolerance":
"Lactose intolerance is the inability to digest significant amounts of lactose, the major sugar found in milk. Lactose intolerance is caused by a shortage of the enzyme lactase, which is produced by the cells that line the small intestine. Lactase breaks down milk sugar into two simpler forms of sugar called glucose and galactose, which are then absorbed into the bloodstream. Not all people deficient in lactase have the symptoms commonly associated with lactose intolerance, but those who do are said to have lactose intolerance.
People sometimes confuse lactose intolerance with cow's milk intolerance because the symptoms are often the same. However, lactose intolerance and cow's milk intolerance are not related. Being intolerant to cow's milk is an allergic reaction triggered by the immune system. Lactose intolerance is a problem caused by the digestive system."
Amy Inman-Felton, RD, a researcher for the American Dietetic Association, wrote in her Apr. 1999 article "Overview of Lactose Maldigestion (Lactase Nonpersistence)":
"[L]actose maldigestion does not mean one is allergic to milk, dairy foods or dairy products. A milk allergy is an allergy related to the proteins in milk, not lactose. Lactose maldigestion does not require a lactose-free or severely restricted diet. Dairy products that provide key nutrients such as calcium, vitamins A and D, riboflavin and phosphorus need not be eliminated."