I do not know why white fabrics turn yellow, but that's why I avoid white as much as I can. I threw a lot of white clothes and thought they were ruined!
And the white pillowcases! They are yellow after a week of use and even with strong cleaning products, I can never have them perfectly white, the white looks dirty ...
Instead of using bleach and a thousand stain remover that never worked, I should have done like this woman who managed to keep her white sheets white, without buying anything!
Her trick is to use baking soda and vinegar in addition to her laundry detergent.
She also adds ¼ cup of baking soda and uses her usual detergent, with the sheets (it also works for white towels and clothes).
Then she replaces the liquid softener with ½ cup of white vinegar.
She washes as usual, without adding anything else.
But when the cycle is over, sheets, towels and white clothes that were stained or yellowed are white!
The before-after photo is impressive!
It's so effective, everyone should do that!