Most children happily avoid hospitals, except for maybe one or two days around the time of their birth. For those few who do return, the instigator is often asthma or its loosely related predecessor, bronchiolitis.
Asthma is an immune phenomenon — an over-reaction to what should be a reasonably – tolerated stimulus. Here is an illustration: three kids walk under a tree in springtime. A gust of wind releases a cloud of pollen that envelops the children. One of the kids revels in the beauty of the event. The second one gets tears in his eyes and a stuffy nose. The third child starts to wheeze.