I darkly suspect 'asthma' to be a generic term for a variety of Weird Things Lungs Do Sometimes. If they give you an inhaler and you say that helps then they put 'asthma' on your notes.

(Before that they give you a flow meter thing to blow into, but if the flow meter thing registers nothing unusual, or in my case, reports a lung capacity that would apparently be adequate to service a small elephant, but you are still complaining and haven't gone away, they give you an inhaler anyway).

The inhaler seems to be kind of like beer for lungs: it just encourages them to relax and loosen up.