Being around allergens can lead to swollen, inflamed airways. You need to control these triggers to prevent asthma flare-ups.
House-Dust Mites: These are a common trigger for asthma. They live in mattresses, bedding, curtains, carpets, & house dust. Cover your mattress & pillows w/special dust-mite proof cases (that zip not just slide in). Use pull-down shades instead of blinds. If possible, replace carpet w/linoleum, tile, or hardwood floors. Use washable throw rugs.
Animals: Choose one taht doesn't have fur or feathers. Keep pets w/fur or feathers out of your home. If you can't do this, keep them out of the room where you sleep. Wash your hands after handling pets (waterless soap is easy to keep in each room & easy to use).
Mold: While bathing or showering, run an exhaust fan or leave a window open in the bathroom. Don't use vaporizers, humidifiers (EXCEPTION: WHEN SECRETIONS ARE THICK, IT IS RECOMMENDED TO DRINK PLENTY OF WATER & RUN HUMIDIFIER WHILE SLEEPING UNTIL SECRETIONS THIN -- THICK SECRETIONS CAN LEAD TO INFLAMMATION OF AIRWAYS WHICH INTURN WILL LEAD TO ASTHMA FLARE-UP), or evaporative coolers (swamp) -- these keep mold/mildew down.
Pollen: Use air conditioning instead of opening the windows in your home/car. If you exercise on days when there is a lot of pollen, exercise indoors. Check local reports for pollen levels ("pollen counts").
Have someone else clean damp areas weekly (showers, etc).
Wash bedding in hot water (130 degrees F) each week.