Exercise induced allergies?

So I've inspired my dad to start running and I am SO proud of him! He's running his first half in just over a week while I run my first marathon :) Anyway, I never run with him so I don't know what his reaction to solo training is, but we've done 3 races together and after each one he gets terrible sneezing fits that last all day! Next day they are gone and he is fine. He's fine before and during the race. 20 minutes later it's like the man has a bomb inside of him that is exploding through is nose lol. Have any of you ever experienced this or know what causes it and/or how to stop it?

This might help.  http://www.medhelp.org/posts/Asthma/Sneezing- after-running/show/272276