Like any other food item, marshmallows also go bad. They hardly last 6 to 8 months after their Best By date. You might have noticed that they get slightly stickier when you leave them open. That's how you know you don't have long until they go completely bad.

How do you know if marshmallows are bad?

How to tell if Marshmallows are bad, rotten or spoiled? It is the texture and color that will change when this product has been around too long. Marshmallows will become sticky and change from a pure white color into a light yellow color when they are going bad.

Why do marshmallows not spoil?

Bacteria actually eat sugar and thrive on it, so it is definitely not the sugar in the marshmallows that kept them from going bad. Your hypothesis is more likely to be true; preservatives do just that--prevent the food from spoiling.