Some people's perfumes set my nose off into sneezing fits which then makes my nose run. It's pretty bad if someone nearby has bathed in that kind of perfume (excessive perfume wearing is inconsiderate and also very un-stylish but that's beside the point here ) even though I take antihistamines. If I'm on long haul and it happens and I can't move seat I take something else to settle it down but it takes it a while for it to settle down. Some airborne stuff sometimes makes me cough as well, without having a cold. I feel really bad about doing that because it might worry people around me that I may be contagious and they may worry that they catch it. But there really isn't much I can do - I keep it as discreet and non-disgusting as I possibly can and dispose of tissues etc neatly and properly.

It's not too bad as long as people are trying to be considerate towards others when they cough/sneeze etc by doing their best not to spread whatever germs they may have. However I do hate it when someone nearby is hacking every 10 seconds or sniffling loudly every 10 seconds - I wish they blew their nose instead of sniffling up whatever... that is definitely not nice (although I do know it's preferred to blowing one's nose in some cultures).