Dust mites can be killed easily by using hot water while washing the pillows. The water should at least be 130°F. If your pillow cannot be washed with water, you can put them inside the dryer at a temperature of 130°F for 15 minutes.  It will kill all the microorganisms and your pillow would be fresh as ever. Before, you take these steps; it would be good to check the instructions on the care label of the pillow.