Nonenal (or 2-Nonenal) was first identified in 2001 by the Japanese cosmetics company Shiseido as the main source of aging body odor. Further studies were documented in the March 2010 issue of the Journal of Biological Chemistry: “Lipid peroxidation generates body odor component trans-2-nonenal covalently bound to protein in vivo.”

Nonenal is produced when lipid acids are oxidized (lipid acids are fatty acids produced in the sebaceous gland). Hormonal imbalances often result in higher production of lipids. As the skin matures, its natural antioxidant protection decreases, resulting in greater amounts of oxidized lipids.

Nonenal can be recognized by an unpleasant, grassy or greasy odor. It is often hard to detect on oneself but will linger on fabrics, such as shirt collars and pillow cases, if not removed during baths. Nonenal odor often persists in confined environments, such as nursing homes, and is thus sometimes referred to as the old people smell. Because this odor is oil (fatty acid) based, it is not easily removed by conventional soaps and water.

Nonenal’s effect can be different in men and women. Many women experience changes in body odor during menopause. This new odor can be a combination of both increased sweat-based odor and nonenal-based odor, leading to confusion and frustration when these odorsare not easily eliminated. Hot flashes and night sweats during menopause cause excessive perspiration and increased fatty acids, resulting in higher production of nonenal.

A recent Swedish study showed that middle aged men often have the worst body odor amongst all age groups in males. This could be due to higher testosterone ratios and related nonenal production. Finally, stress can also exacerbate the production of nonenal in both women and men.