Photo by pmarkham.
Pillows have a limited lifespan. If you can't remember the last time you replaced yours and want to quickly see if it's time for a new one, try this simple test.
Real Simple recommends:
Fold your pillow in half, squeezing out the air. If it doesn't spring back to shape, you're overdue for a new one. Otherwise, so long as they don't smell mildewy, you only need to replace your pillows every three to five years -- any longer, and they begin to lose support.
Pillows are also one of those things that can accumulate nasty stuff like dust mite remains and dead skin, so even if your pillow does bounce back in shape, it's a good idea to replace it every few years. When it's time, make sure you buy the right pillow for your sleep position.
When to Buy a New Pillow [Real Simple]