Because of dairy foods’ natural combination of essential nutrients (1), these foods are a key component of dietary guidance issued by the U.S. government and supported by several health organizations (2-6). Unfortunately, some individuals may experience adverse symptoms following intake of cow’s milk and other dairy products (7-10).

There are two general causes of reactions to cow’s milk: cow’s milk allergy and lactose intolerance. Cow’s milk allergy is an immunologically mediated response to one or several of cow’s milk proteins (7,8). Lactose intolerance, a non-immunological reaction, is the occurrence of symptoms after persons with clinically diagnosed lactose maldigestion (i.e., low levels of the intestinal enzyme, lactase) consume lactose (milk sugar) in amounts exceeding lactase’s ability to hydrolyze it into glucose and galactose (7,9,10).

Misperceptions and confusion surround cow’s milk protein allergy and lactose intolerance (7-10). Also, many people overestimate the prevalence of these reactions to cow’s milk (11,12). A population-based study among 827 young adults in Finland found that although the majority of subjects who reported gastrointestinal symptoms blamed milk and milk products and reduced their intake of these foods, cow’s milk was rarely responsible (11). Researchers in Australia reported that the self-diagnosed incidence of cow’s milk allergy in a population was ten-fold higher than the clinically diagnosed prevalence (12). Failure to understand reactions to dairy products can lead to unnecessary dietary restrictions and adverse nutritional and health effects (4,8-10).

Misperceptions related to adverse reactions to cow’s milk can lead to the unnecessary restriction of dairy products and potentially compromise nutritional status and health.

This Digest reviews the cause, prevalence, prognosis, clinical symptoms, diagnosis, and management of cow’s milk allergy and lactose intolerance. Because of cow’s milk’s nutrient density and health benefits, it is important to accurately diagnose the cause(s) of any symptoms following intake of dairy foods and manage the condition without compromising nutritional status. Fortunately, reactions to milk and other dairy foods affect only a relatively small proportion of the total population and generally are prevented by dietary strategies.

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