American cheese is pasteurized and thus doesn't age like other types of cheese, including the cheeses that it's made from, such as Colby and cheddar. Canned, squeezable and some sealed loaves of processed cheese don't require refrigeration until after they are opened. Processed cheese slices and cheese food, including American cheese, do require refrigeration. Refrigeration between 35 and 40 degrees Fahrenheit keeps your cheese slices, whether individually wrapped or not, fresh and free of mold and bacteria.

American cheese is considered a semi-hard cheese and does eventually expire. If unopened, it lasts up to one month after its printed expiration date; it lasts two weeks if opened. If you notice any change in your American cheese slices' texture, odor or flavor, throw them away. Visible mold is also a sign of spoilage; you need to discard any moldy slices. Freezing your cheese at 0 F can extend its shelf life to around three months, but will change its flavor and texture, making it more appropriate for cooking than use by itself.