Diana
"The Farm Effect" is a name scientists coined to describe the good health of farming families.
Experiment with two identical populations of chicks, a sterile environment kept clean and an identical environment in which the chicks were sprayed with barnyard muck. The muck sprayed group was healthy. The sterile group had asthma, allergies and autoimmune disorders.
"...the Indiana Amish among the least allergic populations ever described in the developed world..." [also one of the least vaccinated developed world populations]
"These days, one in five American children have a respiratory allergy like hay fever, and nearly one in 10 have asthma....Nine people die daily from asthma attacks. -http://www.nytimes.com/2013/11/10/opinion/sunday/a-cure-for-the-allergy-epidemic.html?pagewanted=all&_r=0
Another risk factor for allergy is genetically modified food.
"On May 19th, the American Academy of Environmental Medicine (AAEM) called on "Physicians to educate their patients, the medical community, and the public to avoid GM (genetically modified) foods when possible and provide educational materials concerning GM foods and health risks."[1]"
Summaries of animal experiments here:
http://www.responsibletechnology.org/doctors-warn
Anecdotally, my neighbor is allergic to milk and milk products, however, fresh raw organic grass fed milk doesn't cause her any issues. My cousin is gluten-intolerant, and almost unbelievably, she can eat fresh ground organic wheat with no reaction. I have seen the same with wool allergies (organic wool doesn't cause the individual to itch) So possibly some of what we call "allergies" are reactions to pesticides, GMOs, processing, and how far removed supermarket foods are from what our bodies evolved to process.
Important to differentiate between and "allergy" (a reaction to a substance generally regarded as safe, say, grass or fleas) and a reaction to a toxic substance. It wouldn't make much sense to say "Doctor, each time I eat cyanide, I have this terrible allergic reaction!"
Likewise, if a dog is allergic to fleas or grass (or a child allergic to dogs) that begs the very important question "Why is this reaction happening for this individual and not for others?"