Dust mites
These microscopic monsters thrive in mattresses and bedding. When their droppings and remains become airborne, your natural filtration system feels under attack.
Mold
This fungus flourishes in dark, damp areas such as basements and bathrooms. When mold spores get into the air, they can trigger allergy symptoms.
Animals
Little known fact: most people aren't allergic to animal fur, but rather to a protein found in pet dander or saliva.