Once your case is clean, a little care keeps it clear for longer. Wash it every week or two, and avoid leaving the phone in direct sunlight, on a car dashboard or in very hot places. Wash your hands before using the phone, and keep it away from sunscreen, hand creams and perfumes, which can speed up discolouration. Remember that cases made from TPU or silicone tend to yellow faster than polycarbonate ones, so if yours is badly aged, replacing it may be the better option.