I had this pretty good as a kid - but my younger brother had it much worse.
Ours (as in most people) is triggered most easily by allergens.
Pets and molds are the most common triggers, but you should have him tested and you should also know that allergies can shift and change over time.
My brother says that having one of those O3 (ozone) machines really helped him the last couple years he lived at home. Ozone is controversial as it can both help and harm - but definately go the extra mile and maintain good airfilters in your A/C system and consider some type of HEPA filter or ionizer to keep the particulates down.
Another thing that may be radical (but as a father, I know nothing is too radical if it makes my baby not be sick) Consider where you live in the country and consider moving. Areas with bad smog are MUCH harder on people with asthma than the rest of the population (and it aint good for them either).
Also - some areas just have more pollen and junk than other areas.
They say now that regular exposure to dogs and cats in the first year cuts the risk of developing asthma in half.
The other thing I would say is - be sensitive to his condition and you may need to break a few (teachers) arms when he goes to school. Brother and I have both had teachers who "did not believe in asthma" or who said in P.E. "just run it off" (the worst thing you can do).
Keep the medicine handy and also make sure he stays in shape - my asthma was almost non existent when I was in excellent condition - so encourage him to stay active (I played football and stuff) but also do not let coached push him to keep going if he gets symptomatic - that can lead to a hospital stay.
If you understand the disease and stay on top of it, you will get through it - some people do die from it, but in my opinion, they are probably not managing the disease properly.
Godspeed.
