Exposure to allergens such as dust mites, cockroaches, mold, pollens, or animal dander can trigger or worsen symptoms in some children with asthma. This is referred to as allergic asthma. Seasonal allergies to outdoor pollens (also called hay fever) won't usually be a problem until your child is 4 or 5, because it can take that long for him to be exposed to enough pollens to develop a sensitivity to them. Allergies to dust mites, mold, or animal dander may develop earlier in life, though.
About 75 to 80 percent of children with asthma also have significant allergies. If your child has asthma and you suspect that he has allergies, you may want to take him to an allergist for further evaluation and treatment that may help prevent asthma attacks.