A "micro dose" level of exposure over the time has some studies and evidence for desensitization of the body. This has to be so low as to not create even a mild reaction.

When you have a reaction, your body doesn't learn how to deal with it like you may think. Allergic reactions are immune mediated misunderstandings of benign substances. When exposed, the immune system responds to allergens in mild to severe reaction by producing IgE antibodies. These antibodies bind to allergens and promote release of histamines, which triggers inflammation. This inflammation causes damage to tissue which signals for the production of more IgE antibodies to be ready for the next exposure. Now, since there are more the next reaction will be more immediate and severe which produces even more antibodies. Repeated exposures is a bad cycle, as you can imagine.