Cheese can be left out for no longer than two hours at temperatures above 40 degrees Fahrenheit, according to EatByDate.com. Once cheese is left out for longer than recommended, it begins to degrade in quality.
Softer cheeses, such as mozzarella and cottage cheese, need to remain refrigerated unless they are being used. Hard cheeses, such as Parmesan and Romano, can stay out for longer periods of time. When storing cheese, it is best to use an airtight container or leave the cheese in its original packaging. When cheese is exposed to air, it dries out and can become moldy, according to the Clemson Cooperative Extension.