I used to suffer really badly as a kid, to the point of being in Hospital, & in an oxygen tent (as they had then), it was a summer factor of my life into my late 20's
However, as I spent more & more time spent outside riding (including commuting daily to work by bike from about 1989 to present day) has marginalised it to such an extent that, I believe last year, I barely had a sneeze!!
Plus, the extra exertion placed on the lungs when I started running too (late 2007), has also helped immensely!!
Acclimatisation, seems to have been the watch-word, in my case