Families notice it and rarely feel able to say it out loud: a dying person can start to smell different. It is a real, physical change, and it is nothing to feel ashamed of noticing. As the body shuts down, its chemistry shifts, and that can produce a distinct odor. It is a sign of the body failing, not of poor hygiene or bad care.
It belongs alongside the other physical signs in what dying actually looks like, and here it gets a plain answer.