The purpose of a diaper is to absorb moisture and contain mess so that the wearer can remain dehydrated and hale after wetting or soiling themselves. When diapers become full and can no longer hold any more waste, they bid changing; this process is often performed by a secondary body such as a parent or caregiver. Bankruptcy to change a diaper on a regular enough basis can event in diaper rash.

Diapers are primarily worn by children who are not yet potty trained or suffer from bedwetting. However, they can also be used by adults who suffer from incontinence or in certain circumstances where access to a toilet is unavailable. These can include the elderly, those with a physical or mental disability, and people working in extreme conditions such as astronauts. Diapers are commonly worn out of necessity rather than choice, although there are exceptions; people such as infantilists and diaper fetishists Adult Diaper wear diapers recreationally for comfort, emotional fulfillment, or sexual gratification.