Wash them! I wash my pillows all the time. Do 2 at a time to keep the tub balanced. Use half the recommended (low suds) detergent, a couple heaping tablespoons of baking soda and NO FABRIC SOFTENER. Use vinegar in the rinse cup instead. I lay in the sun between old sheets or beach towels to dry. Then on "fluff" - no heat to puff them back up. I even wash the down pillows my mom made in 1957.
Hi Mary, the best way I have found is to use VERY hot water to which you've added the usual amount of laundry detergent 1/2 cup of borax, 1/2 cup of Oxi-Clean, and 1 cup of automatic dishwasher soap. Be sure those ingredients are mixed well and then submerge your pillows in the hot, hot water. Close the lid and let soak for a while. You can also add some boiling water into the mixture and swish the pillows around as they soak some more. Then let your washer agitate and run as usual. After finishing the spin cycle place your pillows outside in a sunny location to dry. Most all of the yellowing areas will be removed. Do it again soon if it is not completely yellow free. The pillows are clean, but maybe a lsight staining may remain. Good Luck!