Is soaking your cup in peroxide occasionally bad for your cup?

daisy

This is the peachlife raspberry cup (medium firmness) and it is my goldilocks cup...but it stains. It looks like this after about 3-4 cycles. I soak it in half peroxide and half water overnight when it gets bad and that takes care of it. Since this is only a cosmetic issue and the cup is in fact clean even if its stained I don't want to keep doing it if its damaging the cup.