The Science Behind the 'Old Person Smell'
Research has identified a natural, biological reason for a distinctive scent associated with aging, sometimes called 'nonenal' or 'old person smell.'. This is a normal part of the aging process and is not an indicator of poor hygiene.
The Role of 2-Nonenal
As people get older, starting around age 40, the body's natural antioxidant defenses on the skin begin to decline. This leads to an increase in the production of omega-7 unsaturated fatty acids on the skin's surface. When these fatty acids are oxidized, they produce a compound called 2-nonenal.
- What it is: A chemical compound that has a distinctive grassy, greasy, or musty smell.
- How it differs: Unlike other body odors that are water-soluble and can be washed away with normal soap, 2-nonenal is not and can cling to clothes and bedding even after washing.
- How it relates to the mothball smell: While different chemicals, the musty and stale characteristics of 2-nonenal can be easily conflated with the smell of mothballs, especially to a younger person with a keen sense of smell.
The Environmental Factor: Actual Mothballs
Beyond the biological reality of 'old person smell,' the literal presence of mothballs plays a significant role in creating this familiar scent profile.
Historical Use of Mothballs
For decades, mothballs were the go-to solution for protecting natural fibers like wool and silk from pests. Older generations grew up with this practice, and many still rely on it for storing clothes or household items.
- Sublimation: Mothballs are made from a solid pesticide, typically naphthalene or paradichlorobenzene, that turns into a gas (sublimates) over time to kill moths.
- Lingering odor: The fumes from these chemicals are designed to be persistent. They can be absorbed by porous materials like fabric, wood, and carpets, where they can linger for months or even years.
- Enclosed spaces: Because mothballs are most effective in sealed containers or closets, the concentration of the chemical vapor is highest in these enclosed spaces. The scent then permeates everything stored within and can spread to other areas of the home.
Why the Smell is so Persistent
The chemical vapors of naphthalene have a very low odor threshold, meaning humans can detect them even at very low concentrations. This is why the smell seems to permeate everything, even if only a few mothballs were used. The persistent smell is often a mix of the gaseous pesticide, absorbed chemicals in fabrics, and the biological nonenal.
Comparison of Causes: Nonenal vs. Mothballs
| Feature | 2-Nonenal (Biological) | Mothballs (Chemical) |
|---|---|---|
| Origin | Caused by the oxidation of fatty acids on the skin as a normal part of aging. | A solid pesticide (naphthalene or paradichlorobenzene) used to repel moths. |
| Scent Profile | Described as musty, greasy, or grassy. Can be confused with mothballs. | Strong, pungent, and distinctive chemical odor. |
| Persistence | Clings to skin and fabrics because it is not water-soluble. | Vapors are absorbed by porous materials, and the smell can linger for months or years. |
| Prevalence | Occurs naturally in many people over the age of 40. | Dependent on historical and continued usage of the product by older generations. |
The Interplay of Factors and Health Considerations
It's the combination of these elements that creates the specific scent memory many associate with their grandmother's house. While nonenal is a natural byproduct of aging, the widespread use of mothballs in previous decades means the two scents often coexist and merge in memory. It's a blend of biology and history.
Health Concerns with Naphthalene
It is important to note that the active ingredients in mothballs, especially naphthalene, can be harmful. The Centers for Disease Control and Prevention (CDC) warns that inhaling the fumes can cause a variety of symptoms, including headaches, nausea, confusion, and more serious conditions like anemia, especially in sensitive individuals. This is why modern pest control methods are often preferred and why proper ventilation is critical when mothballs have been used. Many countries, including the UK and EU, have banned naphthalene mothballs due to these concerns.
Conclusion: More Than Just One Smell
The iconic "Why do grandmas smell like mothballs?" question is answered by understanding that it is a multi-faceted phenomenon. It's partly a normal biological process tied to aging, the production of the compound 2-nonenal. But just as significantly, it is the lingering residue from decades of using actual mothballs to protect cherished belongings. The combination of these two scents, one physiological and one environmental, is what has etched this particular aroma into our collective memory. The smell is a sentimental reminder of a specific time and generation, a blend of their biology, their habits, and the physical spaces they inhabited.
