What is the primary purpose of a bottom sheet on a bed?

The primary purpose of a bottom sheet on a bed is to protect the mattress. This layer not only acts as a barrier between the sleeper and the mattress, preventing oils, sweat, and other substances from directly contacting the mattress, but it also helps in maintaining hygiene by being easily washable. Keeping the mattress in good condition is essential for its longevity and comfort, making the bottom sheet a key component of bed linens. While warmth, decoration, and comfort are important aspects of bedding, the specific and primary function of the bottom sheet is to act as a protective layer for the mattress itself.