I posted a couple weeks ago about allergies and parasites. More research on the allergy front indicates a possible mechanism to prevent, at least some, allergies.
There is a lot of research going into probiotics these days. They have been linked with all sorts of health concerns as a possible means of prevention, or at least reduction of symptoms. Turns out they have been connected to allergies as well.
A 2013 study reviewed the current literature and found that combined prenatal and direct postnatal supplementation of the infant with probiotics decreased rates of eczema until the age of 2 with some extended effects showing until the age of 4. These effects found that the strain Lactobacillus rhamnosus showed the most consistent effects. (http://www.medscape.com/viewarticle/804455)
On the other hand, a 2010 review showed that the results are inconsistent and depend heavily on the type of bacterium, dosing regimen, delivery method, and host factors such as the age and diet of the host. In addition, many allergies have different phenotypes (how genes are expressed – blue eyes is a phenotype) which further complicates the issue. (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2883099/pdf/cei0160-0295.pdf)
The World Allergy Organization, with McMaster University reviewed controlled trials of probiotics for the prevention of allergies. They found that the current evidence does not indicate that probiotic supplementation reduces the risk of allergies when given during pregnancy and breast feeding, or to the infants themselves. Eczema was the one exception that they believe there is probably a net benefit of using probiotics for. (http://www.biomedcentral.com/content/pdf/s40413-015-0055-2.pdf)
So, no one said that there is no connection between allergies and probiotics, but it certainly isn’t a clearly beneficial relationship. And as for research on adults, I couldn’t find anything that even evaluated the situation to come up with an inconclusive result.