"Reverse the problem" is severely overstated. Admittedly it can be useful for people with potentially-fatal allergies, but otherwise it's often the equivalent of building scar tissue.

Living in a tropical country, I found myself with increasingly bad allergy symptoms. I went to a doc and had an allergy panel done that clearly showed I was allergic to a weed that flowers all year around (boo). They gave me a nasal spray steroid that, to my utter astonishment, quickly and permanently cured the allergy, with zero side effects.

I know I was lucky, but the point is that yes, it is sometimes possible to "reverse the problem".