It's not unusual to notice that old people can have a certain odor about them. Sometimes called greasy, sometimes grassy, it can linger in the homes of the elderly. It seems that smell is caused by a particular chemical that is made when skin cells start making more fatty acids, which get broken down into a chemical called nonenal. That process, explained in depth in the video, begins to happen around age 40.
The reasons why we make more of those fatty acids is not known, however. Some scientists are even skeptical that this is the definitive cause for the smell.
That hasn't stopped one cosmetics company, however. The Shiseido Group made a fragrance specifically to target nonenal.