Coffee has both caffeine and sugar which are patm triggers to set off your condition. As to why you start sneezing shortly after drinking coffee I have an opinion which comes from my own experience. I believe that the heat from the coffee opens up our pores in our skin and that ammonia like smell is released more than it usually is. You know the smell I'm talking about, the one that makes people itch their nose and cough. I could be wrong, but like I said earlier, this is only my opinion.