From the journal of allergy and clinical immunology:

Background

Farmers’ children have a reduced prevalence of allergic disorders. The specific protective environmental factors responsible are not yet identified. Objective

We sought to determine whether farmers’ children in the rural county of Shropshire, England, have a reduced risk of atopy and, if so, to identify the factors responsible. Methods

The Study of Asthma and Allergy in Shropshire was a 2-stage cross-sectional study. In stage 1 a questionnaire to elicit allergic status, diet, and farming exposure was completed by the parents of 4767 children. In stage 2 a stratified subsample of 879 children underwent skin prick testing and measurement of domestic endotoxin. Results

Compared with rural nonfarming children, farmers’ children had significantly less current asthma symptoms (adjusted odds ratio (OR), 0.67; 95% CI, 0.49-0.91; P = .01) and current seasonal allergic rhinitis (adjusted OR, 0.50; 95% CI, 0.33-0.77; P = .002) but not current eczema symptoms (adjusted OR, 0.91; 95% CI, 0.68-1.21; P = .53) or atopy (adjusted OR, 0.68; 95% CI, 0.40-1.16; P = .15). In contrast, current unpasteurized milk consumption was associated with significantly less current eczema symptoms (adjusted OR, 0.59; 95% CI, 0.40-0.87; P = .008) and a greater reduction in atopy (adjusted OR, 0.24; 95% CI, 0.10-0.53; P = .001). The effect was seen in all children, independent of farming status. Unpasteurized milk consumption was associated with a 59% reduction in total IgE levels (P < .001) and higher production of whole blood stimulated IFN-γ (P = .02). Conclusion

Unpasteurized milk consumption was the exposure mediating the protective effect on skin prick test positivity. The effect was independent of farming status and present with consumption of infrequent amounts of unpasteurized milk. Clinical implications

Unpasteurized milk might be a modifiable influence on allergic sensitization in children.

Found via this article on Salon. Both are behind paywalls, unfortunately. The abstract is free, at least.

The bottom line is that raw milk (unpasteurized) seems to have significant positive effects on your immune system. Just being a farm kid doesn’t, which is mildly surprising. Personally, we had a lot of raw milk when I was school-aged, and I wonder how that affected me. I was quite healthy and had no allergies at all growing up, though my older sister did have hayfever.

Interesting reading, and thought-provoking. It does seem that you have to be pretty careful if you want to try it, as your suppliers need more care in handling, feed, pastures and so forth.