The Only Acceptable Reason For Cereal to be Moist is If it has been Milk-Soaked.
When stored in the refrigerator, cereal will spoil in the same way that bread will. Because of the low temperature and high humidity, the sugar flakes will turn into crystals, and the cereal will become mushy. The worst thing that could ever happen to you is for your cereal to become milk-soaked and soggy.
Cereal can be stored at room temperature for a period of six to eight months without having to be opened. It only needs one week in the refrigerator to maintain its freshness. According to Emily Broad Leib, director of the Harvard Food Law & Policy Clinic, cereal does not go stale even if it is left out at room temperature overnight. Simply put, it becomes less tasty and more stale over time.