The conditions lactose intolerance and milk allergy, which together affect around 30 to 50 million Americans, are often confused. However, the conditions have very different causes and symptoms.

Lactose intolerance or milk intolerance

Lactose intolerance describes a digestive condition that prevents a person being able to digest lactose, a type of sugar present in milk and dairy products.

Normally, lactose is broken down by an enzyme called lactase. Lactase breaks down the lactose into two simple sugars, glucose and galactose, which are readily absorbed into the blood stream to be utilized in bodily functions.

People with lactose intolerance have a deficiency of the lactase enzyme meaning that much of the lactose remains in the gut without being absorbed. It is then fermented by bacteria within the gut which causes a build up of gas and leads to bloating and flatulence. The fermented lactose irritates the inner walls of the gut causing nausea, vomiting and diarrhea.

Milk allergy

In the case of milk allergy, a person is allergic to the proteins present in milk rather than to the lactose in milk. Individuals with milk allergy can therefore ingest lactose if it is separated from milk proteins, which is the case with some processed milk products. Milk allergy describes an actual allergy as opposed to an intolerance.

Difference in age of onset

Lactose intolerance may develop in either children or adults but rarely before the age of two. Lactose intolerance is a lifelong condition and is more common in certain ethnic groups, specifically American Indians, African Americans and Asians.

Milk allergy on the other hand, is more commonly seen in babies before 1 year of age with symptoms usually subsiding once the child grows older and rarely persisting into adulthood. Onset is rare after the age of two. Unlike lactose intolerance, there are no special racial or ethnic groups that show a higher prevalence of milk allergy.

Difference in symptoms

People with lactose intolerance usually develop symptoms such as diarrhea, nausea, vomiting, bloating and increased flatulence when they ingest milk or milk products such as cheese, yoghurt or butter.

In contrast, milk allergy gives rise to typical symptoms of allergy when milk is ingested such as hives, swelling of the face, lips and tongue, and skin reactions such as atopic dermatitis. In babies, the symptoms are often severe colic, vomiting and eczema around the mouth or diaper area. The baby may also cough, wheeze and in cases of severe reaction where there may be a swollen throat and larynx, the baby can have difficulty breathing and start to turn a bluish colour. This is called anaphylaxis.

Difference in treatment

One similarity in the management of both milk allergy and lactose intolerance is avoidance of milk and milk products. For lactose intolerance, lactase enzyme tablets and drops are available that can substitute for the lack of the enzyme. Milk allergy however, is treated using anti-allergy medications such as antihistaminics and adrenaline injection in the case of severe allergic reactions.