I have severe allergies to all furries but i take antihistamines that keep it in check. The one that works for me is Zirtek - which has the active ingredient citirizine hydrochloride (my spellings of these may be a bit off!) its the only one that works for me, whereas my mum take Clarityn which is loratidine i think, so it may take a bit of trial and error in finding the antihisitimine with the right active ingredient in it for your OH.
I have also taken in the past as someone has mentioned, beconase nasal spray to stop the sneezing and streaming nose, as well as eye drops, cant remember what they're called now!
Does your OH have asthma or does the allergy trigger asthma too?
If so a ventolin inhaler which is a reliever would treat any tightness in the chest but a preventative (I have seretide) inhaler is also very effective at lessening a reaction. It may be worth your OH going to the docs and getting advice and also a skin test to maybe find out if it is hay or bunny or both etc.
I am highly allergic to furries, so much so that i was advised by a consultant not to have pets. But I cant imagine life without them, it would be just wrong! So I take antihistimines, prob more long term than is advisable, but it works for me!
SO there is hope for your OH it can be managed in most cases I think, good luck x