One of my kids used to have seasonal allergies. I think allergies make the nasal passages and sinuses swell. Then whenever he got a cold, things couldn't drain properly because of the swelling, so he'd get a really yucky infection. I remember the doctor explaining that his head was like a swamp (we called him "ol' swamp-head")--a breeding ground for bacteria. We used to give him zyrtec for a few days whenever he got a cold so that his allergies wouldn't prevent drainage. Does that make some sort of sense? I know it's a little vague...

Abby