The reason why Mid-Autumn moon cakes can't be eaten after three months is that they have expired or deteriorated. Expired moon cakes will lose their flavor, harden, dry or produce bad taste, and even cause food poisoning. In order to ensure food safety and quality, it is recommended to eat moon cakes within the shelf life and follow the manufacturer's storage suggestions. If the moon cake has exceeded the shelf life, it is not recommended for health reasons.