What causes an elderly person to wet their pants?

Incontinence: There are several types of incontinence: stress, urge & overflow come to mind. Stress is more common in women while overflow is in men (think big prostate). Infection is common cause as is dementia (they don't know better or can't find toilet). Functional incontinence is someone who can't get to toilet in time. This is not same as urge. Think of someone who just had joint replacement.