It is a chemically distinct odor which common to all elderly people. Body odors evolved when chemicals produced from skin glands get broken down to small odorous molecules that release into the air. The specific chemical compound called 2-nonenal
gives old smell , which created by the oxidative breakdown of another complex compound overtime. According to researchers, this 2-Nonenal compound tends to increase with aging, and form more unpleasant greasy odor.