Keep your baby's room as dust-free as possible. Pull up the carpets. Cover hardwood floors with a scatter rug. Make sure bedding and bumpers are not made from feathers. Clean frequently to keep dust to a minimum, though it's not really the dust itself that's a problem but dust mites.
Dust mites survive and thrive on minute particles of human skin.
To keep the mites at bay, cover the crib mattress in plastic and wash all bedding frequently in hot water. Launder stuffed animals frequently, too. Let your child spend as much time outdoors as possible. As asthma is more common in homes with gas ranges, use the fan when you're cooking with a gas range. Avoid using your fireplace or wood stoves.