You probably have several items that are part of your daily life that are hard to whiten. Although, they used to be white, now they tend to gray or yellow, and it need to change. It is unattractive to serve a coffee or food to your guests in discolored dishes or worse, to invite them to sleep at home in a bed with yellowed pillows and yellowish mattress.
Avoid taking bleach to launder your sheets. Use a ¼ cup of lemon juice added to your laundry.