Not all allergens work by inducing B cell IgE production and subsequent release of histamines by mast cells. Poison ivy and poison oak, for example, produce an oil which is absorbed through the skin. Once absorbed, the oil causes a T cell to release chemicals that cause inflammation and other allergic responses. This is an area of open debate and intense research. It is clear that some of the cause is genetic.
People seem to inherit allergies, most often from their mothers.
At least 3 genes are believed to be responsible for allergy, but only one putative gene has been identified. The most effective way is avoidance. Don't go near what you are allergic to if you can help it. If your cat makes you sneeze and you avoid your cat, you will stop sneezing since there is no cat saliva to cause IgE production. If you are allergic to pollen, take refuge in sealed, air conditioned building.