Breastfeeding and Allergies: an Overview

Food allergies are thought to begin when foreign proteins enter the bloodstream through the walls of the baby's intestines, causing sometimes mild, and sometimes life-threatening reactions.  Breastmilk has several different immunoglobulins that help to protect against allergies.  The most abundant immunoglobulin, IgA, binds to the foreign proteins, preventing them from passing through the intestinal wall into the bloodstream and causing allergic reactions.  By the time the baby is 6 to 9 months old, s/he has begun to produce IgA on her own, but until this time breastmilk is her only source of this wondrous substance. 

In addition, during the entire time the child is breastfed she is being passed antibodies to pathogens in her mother's milk.  These are only a few of the many processes that help protect a breastfed baby from allergies.  Thorough  information can be found in many excellent books on the topic.  In addition, the following references will show the actual benefits of breastmilk in fighting allergies.

References

1)
Breastfeeding, even for short periods was clearly associated with lower incidence of wheezing, prolonged colds, diarrhea, and vomiting.
Merrett, T.G.,
"Infant Feeding & Allergy: 12 Month Prospective Study of 500 Babies Born into Allergic Families".
American Allergies, 1988.

2)
Eczema was less common and milder in babies who were breast fed (22%) and whose Mothers were on a restricted diet (48%). In infants fed casein hydrolysate, soymilk or cows milk, 21%, 63%, and 70% respectively, developed atopic eczema.
Chandra R.K.,
"Influence of Maternal Diet During Lactation and the Use of Formula Feed and Development of Atopic Eczema in the High Risk Infants".
Br Med J. 1989

3)
"We conclude that breastfeeding is prophylactic against atopic disease, the effect extending into early adulthood. Breastfeeding for longer than 1 month without other milk supplements offers significant prophylaxis against food allergy at 3 years of age, and also against respiratory allergy at 17 years of age. Six months of breastfeeding is required to prevent eczema during the first 3 years, and possibly also to prevent substantial atopy in adolescence." The article also states that the differences by infant feeding method were so pronounced that it "suggested an influence of early milk feeding that may exceed the heredity burden."
Saarinen UM, Kajosaari M.
"Breastfeeding as prophylaxis against atopic disease: prospective follow-up study until 17 years old."
Lancet 1995; 346:1065-69. []

4)
Formula given to newborns in the hospital nursery contributed to the development of subsequent cow milk allergy among infants who were exclusively breastfed thereafter.
Host A., et al. "A prospective study of cow's milk allergy in exclusively breastfed infants."
Acta Paediatr Scand 77:663-670, 1988 []

5)
PAC is associated with formula-feeding and supplementation.
Israel D, et al.,
"Protein induced allergic (PAC) colitis in infants."
Pediatr. Res. 25:116A, 1989. [)