Until I became an adult and realised that the white pillows I once bought became yellow overtime.
Which isn't surprising of course. Let's be honest with each other.
Pillows get the worst treatment ever. They get drooled on, sweated on... beaten.. you name it.
Thanks goodness that theres a pillow case to save it for the worst...
However, it was till when I moved to my own place that I heard that pillow cases are not enough.
And that you should wash the pillows at least every half a year. Mind you, not every pillow is washable. Check the labels attached to your pillow.
To answer my own question, since my pillows are washable and I have a washing machine, I washed them a month ago. And I regularly repeat this every 3 months.
I will replace my pillows when the zipper that keeps everything intact breaks or when it starts shedding...
...Or when it's getting a tad bit too soft. I like my pillows hard!