Honey and Hayfever/Asthma

Quite a few of the people who buy honey from me do it because of the theory that eating local honey is a remedy for hayfever/asthma. The idea is that the pollen in local honey in some way immunises you, or perhaps that it makes the body less likely to react to it. Its a plausible thoery, and may even be true, though I never actually use it to advertise because it probably amounts to making unsustainable medical claims.