I’ve only toured three times in my career.
Every time I got sick at some point.
You’re constantly around people. You’re constantly shaking hands with people. You’re constantly in new places, with different pollens, with different environments.
Your body isn’t going to be used to this, unless you tour 10 months out of the year and chances are you don’t.
Before you leave and hit the road make sure you have allergy medicine. Get antibiotics if you think it will be necessary. Make sure all of your medical needs are taken care of. Make sure your tour manager is aware of any medical needs you might have. If you don’t have a tour manager (I’m for hire ;) ) make sure you tell at least one other band member about the medical needs you have.
Touring is a lot of fun but take it from my experience, nothing is fun while you are so sick you can’t breathe, or stop coughing, or stop sneezing.