What’s That Fuzzy Thing in the Fridge? Ever wonder whether that opened jar of tomato sauce or mayonnaise in your fridge is still usable? The expiration dates pertain to the unopened product. Here's a list of common foods and approximately how long they last in the fridge after opening -- Pasta Sauce: Tomato-based sauces are good for only about five days to a week after opening. Even if you don't see mold in the sauce, it could actually be in there. No amount of cooking will kill the toxins in mold, so it's best to discard the sauce. Mayonnaise: With its high fat content, mayo is susceptible to mold and bacteria growth, but it can last about two months in the fridge once it's been opened. Cheese: Depending on the type of cheese, whether it's hard or soft, it can last one to four weeks in the fridge. Softer cheeses, like Brie, have a shorter shelf life than hard cheeses, like Cheddar. To prolong the shelf life of cheese, take it out of the plastic it comes in, wrap in wax paper and then a layer of plastic wrap and keep refrigerated. Eggs: Eggs can last three to five weeks in the fridge. Keep them in the coldest part of the fridge, usually the back. Keeping eggs in the door, where some manufacturers put those "egg shelves" will cause them to spoil more quickly. Leftovers: Most leftovers can last three to four days in the fridge. If you have a large amount of leftover hot food, divide it into smaller portions in separate containers in the fridge to ensure that the middle cools down properly.