By Ariane Sohrabi-Shiraz Over time our duvets and pillow cases can become grim and horrible from the sweating we do overnight – and it can be a pain to clean. It’s normal for white duvets to yellow over time, as they absorb whatever liquid comes into contact with them – from sweat to lotions and cream. You might think you have to splash out on expensive cleaning products to get the unsightly yellow, orange or brown stains off, but that isn’t the case. A cleaning expert has come up with an incredible cleaning tip which can help banish these stains from your duvet – and clean your washing machin…