I am a chronic asthmatic, or at least i was growing up, my medical file is thicker than a phone book and i was in and out of hospital a dozen times a year. Its much better nowadays but i of course still have it, you never really lose it but it can be managed.
When i moved out of home it got a lot better, i managed and controlled my environment to be very clean, and of course back at parent place they had animals i was allergic to, cats, dogs, rabbits and guinea pigs which didnt really help.
Ideally a hyper clean environment with no animals, no flowers or any bullshit, lots of fresh air and not living in the city would mean i have minimal symptoms. Medication like seritide help control it, and ventolin when you wheeze. Also fitness helps a lot.
I would say its partly genetic as my dad has it, and my uncle on my mums side died from it, but also environmental as its worse during spring with all the pollen, or during winter if i let my chest get cold. The worst thing is dust, keep it away and keep a clean room, sleep with the window open etc.