Why is brown sugar hard and how can it be softened for use in baking or cooking?

Brown sugar hardens due to the moisture content evaporating over time, causing the sugar crystals to stick together. To soften it for use in baking or cooking, you can place a damp paper towel or a slice of bread in the container with the brown sugar and seal it tightly. Alternatively, you can microwave the brown sugar in short intervals with a damp paper towel to help rehydrate it.