Probably more than you wanted to know. http://www.ncbi.nlm.nih.gov/pubmed/16498856 If your gloves aren't enough, you can always carry a bandanna in a pocket or tied around your handlebars.

It's not necessarily allergic, but if it only happens to you at certain times of the year it likely is. Molds are also very high this time of year, and though I don't know for sure, I would think the damp climate of the PNW would be particularly susceptible to molds.