So, you wash your hands when they are dirty, right? You wash your arm pits when they stink, right? There's a long list here, but I will get to the point quickly.
A lot of my cycling homies complain about allergies and how they increase when they ride. They take allergy meds and then feel not so clear.
I solved this problem by putting a bottle of saline nasal wash in the shower. I simple hose the nose whenever I'm in the shower. Since I always shower at some point after a ride, I get my pits clean and my nasal passages.
You see, the saline wash cleans the nose out but also provides extra defense against those pathogens that make it into the nose. Most viruses and bacteria that affect humans are not stable in salt water.
I am an allergy suffer as well, but a gentle wash does the trick there, too. It also is extremely effective right after I mow the yard.
Be sure to buy something that is 100% saline. Watch for the "preservatives" that can act as a drying agent. Ask a pharmacist if you are not sure and definitely ask before using it on a child, preggo, etc. Just ask. My doc said it was cool for me, but my doc is not yours. That's as legal as I am going to get.
Good luck.