DH gets sick from the a/c all the time at work. It's mainly because it dries out the mucous membranes in your resporatory system (inside your nose and throat) and this makes the area easier for germs to grow as mucous is a defence against them. Also if the body is subject to extreme changes in temperature it has to work harder to regulate itself... this also exhausts the bodies natural defences. it's always better to adjust the temp gradually... not step from a hot place into a cold room and visa versa... when you have a/c it makes the change too sudden. So yes, people in a/c spaces often do get sicker but you have to balance that with the potential for dehydration and illness associated with heat fatigue. tricky.