Dust mites can be found wherever there is dust. They thrive most, however, in places where the humidity is high and where human dead skin flakes can be found, such as bed linens, carpet and upholstered furniture. Another reason dust can be such a powerful asthma trigger is that it often harbors other allergens, such as pollen and animal dander.
If you are allergic to dust mites, then your asthma symptoms are likely to be active year round. The reason for this is that dust is always around, so it's difficult to escape contact with it completely. There are some, however, actions you can take to avoid dust mites.