The science behind ‘old person smell’
Q: I am a 74-year-old man with a somewhat embarrassing question. My grandson recently asked me why I smell dusty. I've heard about “old person smell,” but always thought I would know if I had it. What causes it? I have good hygiene. Why doesn't that prevent it?
A: Whether it's bad breath, perspiration or any other scents our bodies produce, the standards of modern hygiene demand that they be eliminated. The when and why of this has its roots in the late 19th century, when advances in plumbing and the science of hygiene (boosted by aggressive advertising by soap manufacturers) introduced the idea of the daily bath.
Today, we have moved far beyond simply staying clean. People of all ages are expected to erase any trace of bodily odor. Unfortunately, as the interaction with your grandson shows, even a slight shift from that olfactory net zero can cause embarrassment.
The scent you are asking about is believed to be triggered by a compound known as 2-nonenol. It has been variously described as smelling musty, grassy, greasy or dusty. Its presence on the body is not related to poor hygiene. Rather, 2-nonenol is a byproduct of chemical changes that occur in certain fats present in the skin. To understand how this happens, we need to dip into biochemistry.
The creation of 2-nonenol begins with chemical compounds called omega-7 unsaturated fatty acids. Human skin produces several types of these, the most abundant of which is palmitoleic acid. It is central to the skin's ability to act as a protective barrier and plays a role in wound healing.
A process known as oxidation can cause a breakdown in certain chemical bonds in palmitoleic acid. When this occurs, one of the byproducts is 2-nonenol.
Due to age-related changes that occur in the skin, older adults can often begin to produce larger amounts of 2-nonenol. The chemical structure of this compound causes it to evaporate readily at room temperature. That means 2-nonenol emits its characteristic scent not only when present on the skin, but also in the air around the person whose skin is producing it.
And because 2-nonenol is a fatty acid, it is not water-soluble. This means that unlike sweat, which is water-based, it is not easily washed away with soap and water. Even for people who practice diligent hygiene, the dusty or musty scent of 2-nonenol can persist. Because 2-nonenol can become embedded in fabrics, it can be helpful to wash clothing and bedding with detergents that are specially formulated to remove grease. Keeping rooms well-ventilated can help diminish the scent of the compounds that have become aerosolized.
Some claims have been made that the tannins present in persimmon-based soaps can successfully remove 2-nonenol from the skin. However, the evidence in that regard is strictly anecdotal.
As for being unaware of this change in your personal scent, it is due something known as sensory adaptation. It occurs because, in order to remain alert for important new information, our brains begin filter out the familiar. It happens to all of us, and is not a cause for alarm.
• Dr. Eve Glazier is an internist and associate professor of medicine at UCLA Health. Dr. Elizabeth Ko is an internist and assistant professor of medicine at UCLA Health. Send your questions to askthedoctors@mednet.ucla.edu.
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