Brown sugar does not go bad but it can become hard once opened.
If the brown sugar does go hard then adding moisture to the brown sugar can fix it.
Brown sugar is best used within 2 years of purchasing but remains safe to use and consume after that for many years.
Brown sugar doesn't expire although brown sugar does has a shelf life of roughly two years but can last longer if you store it properly.
If you have kept your brown sugar in the pantry for several years, you can still use it as long as there is no bug contamination, bad smells, or mold growing.
Over time, even in an airtight container, brown sugar can harden and/or start to turn white (as the sugar dries, some of the molasses separates.
Creating a humid environment will allow the brown sugar to rehydrate to become pliable and brown.
To quickly soften brown sugar: place the sugar in a microwave safe bowl and cover it with a damp paper towel for about 20 second, or use a food processor to loosen the brown sugar.
If you aren't pressed for time, use a slice of bread or an apple in an airtight container with the brown sugar for 24 hours.