Mostly, yes. My only concern would be is if horses are the only thing you are allergic to in the barn? I have allergies as well, and have my own horses, so can relate to the struggles! Some barns are fine, but others can make a mess out of me! In particular, I've found certain hays and also dust to be a trigger. I try to pick barns with good ventilation to board at and this is also beneficial for the horses for many other reasons.
However, unfortunately I can't always avoid allergy triggers, so I do carry allergy pills with me. Both long-acting, such as Reactin and shorter acting <24 hours as well. I also carry clean up wipes for after. If the barn has a wash room, I always wash my hands before leaving, but If not, I have little portable hand wipes to use after. I find if I do not clean my hands and face, then It gets worse. The other tip I have is to groom/ handle the horses with gloves and wear long sleeved sun shirts!