It used to be that allergies were somewhat rare but if you go to an allergist today, you are almost certain to be declared allergic, or at least sensitive, to something. How much of that is actual biological change versus how much is that the country that purchases 85% of the world's prescription medication loves to get medical diagnoses is unclear.

Now the European Academy of Allergy and Clinical Immunology believes that nearly half of the population of the EU have allergies to something. A survey of Americans in 2020 estimated that approximately 30 percent of Americans of all ages have allergies. Since they are self-reported surveys rather than dianoses, what is unclear is how many of those are people claiming issues like gluten sensitivity.

A new observational paper argues that one reason for more allergies may be the thing that also caused foodborne illness and death to plummet; pasteurization. They made their assertion comparing breast milk from Old Order Mennonites and urban mothers and then correlating that to allergies. Old order Mennonites do not form a consistent group but are generally more modern than the Amish, so won't have something like a television or radio but may use cell phones and computers. They can use cars. Vaccination is not prohibited but many dismiss vaccine-preventable diseases as something like "whooping cough season" rather than a real worry. They live primarily on farms but the participants used modern prenatal care enough that they visited a clinic and 52 mothers agreed to donate breast milk, which was compared to 29 mothers with a modern urban lifestyle in the nearby city of Rochester. 

Questionnaires and follow-up phone calls asked moms about their lifestyle and environment, and whether they or their babies had any symptoms of atopic diseases. They then measured the milk’s concentration and activity of IgA antibodies – linked to protecting the respiratory system and gut against microbes – as well as the concentration of oligosaccharides, cytokines, and metabolites of fatty acids. They used ribosomal RNA gene sequencing to determine which species of bacteria were carried from mother to baby in milk.

Mennonite mothers self-reported a greater exposure to farm animals, dogs, raw (not pasteurized against bacteria) milk, and barns, a higher rate of giving birth at home, more use of bleach and less use of antibiotics and pesticides. They also reported a lower rate of atopic diseases for themselves and their babies.  

Analyses found breast milk from the old order Mennonite mothers contained more IgA1 and IgA2 antibodies against peanut, egg ovalbumin, dust mites, and the bacterium Streptococcus equii, a pathogen of horses. The milk from Mennonite mothers contained milk microbes, such as bacteria from the families Prevotellaceae, Veillonellaceae, and Micrococcaceae, and higher concentrations of certain oligosaccharides and fatty acids.

The authors contend that greater exposure to bacteria may be why those communities report fewer allergies. While that may be true, raw milk causes 700X more food poisoning cases than milk that has been treated to remove harmful bacteria. Kids on farms who got Hepatitis A likely got it when they were young and don't remember it, but it can certainly be far more risky for older adults who grew up in cities.