Allergy bedding is usually the first thing an allergist recommends after being diagnosed with allergies. The best covers are effective against dust mites, bed bugs, pollen, pet dander and other allergens.
The mattress and pillow covers are made to keep dust mite allergens out of your bed or keep the ones already in it from messing with your allergies.
Additional information: Allergy Bedding | Step #1 in Fighting Dust Mite Allergies