Pillows are prime growing ground for mold and dust mites. Mold enjoys damp conditions and pillows are porous and absorbent. The moisture from sweat, saliva and breath gets into the pillows and mold starts to form. Dust mites consume dead skin cells in pillows and other bedding. Pillows are often left behind when the rest of the bedding is washed and they aren't replaced frequently, so mold and dust mites continue to thrive. The good news is mold and mites can be killed with a hot water wash, and both synthetic and feather pillows can be washed in the washing machine.
Add your usual laundry soap to the washing machine and fill the washer with hot water. Use the hottest water setting your washer has. In order to kill dust mites, the water needs to be 130 degrees Fahrenheit. If your water isn't this hot, you can turn the temperature up on your hot water heater.
Add the pillows to the washing machine. Wash two pillows at a time to keep the load even.
Add 1 cup of bleach to the wash. Use your bleach dispenser if your machine has one. Otherwise, add it to the water.
Run the washing machine through a gentle cycle.
Remove the pillows from the washer and put them in the dryer. Dry them on high heat until they are thoroughly dry. Every 20 minutes or so, remove the pillows and fluff them to keep them from bunching.