Which factors in raw cow's milk contribute to protection against allergies?

Several epidemiologic studies have shown that growing up in a farming environment is associated with a decreased risk of allergies. A factor that correlates strongly with this effect is the early ingestion of unheated cow's milk. Although, to date, no controlled studies on raw milk consumption have been performed to formally demonstrate this effect, several factors in bovine milk have been described that might explain how raw cow's milk consumption can decrease the risk of allergies. In addition, increasing knowledge on the immunologically active factors in breast milk have also contributed to our understanding of the effects of bovine milk in infants because many of the factors in bovine milk are expected to have functional effects in human subjects as well. Here we review these factors and their mechanisms of action and compare their presence in bovine milk and breast milk. A better understanding of these factors, as well as how to retain them, might ultimately lead to the development of mildly processed milk and infant nutrition products that could become a part of preventive strategies to reduce the incidence of allergic disease. (J Allergy Clin Immunol 2012; 130:853-8.)