What Causes “Old Person Smell”?

iStock / Koldunov
iStock / Koldunov

Reader Sarah writes in to ask, “What is it that causes that distinctive 'old person' smell? Whatever it is, it seems to be common to all elderly people. Is it inevitable or is there something you can do to avoid it?”

Ever notice that your grandparents and their house had a dull, kind of sweet stink to them? You’re not alone. Old people really do have a chemically-distinct odor.

Like other body odors, this “old person smell” is produced when chemicals from the skin glands get broken down into small odorous molecules that waft away into the air. The specific chemical that gives old folks their unique odor, scientists suspect, is a compound called 2-nonenal. Created by the oxidative breakdown of other chemicals over time, it produces what’s described as an “unpleasant greasy and grassy odor” in people and is also responsible for some of the “cardboard” flavor of stale beer.

In 2000, Japanese researchers found that people’s concentration of 2-nonenal increased with age. They had 22 people, ranging in age from 26 to 75, wear odor-collecting shirts to bed for a few nights and then analyzed the molecules that adhered to the cloth. They found more 2-nonenal in the shirts worn by people over 40 years old than they did in the younger subjects. And in the over-40 crowd, the concentration of 2-nonenal increased significantly with age, with the oldest subject producing almost three times as much as the middle-aged subjects. 

The researchers didn’t see any other odor compound increase with age like that, and think that the “deterioration of body odors” in the elderly, as they politely put it, can be pinned on 2-nonenal. But why does the compound increase as a person ages? The researchers also noted the presence of more omega-7 unsaturated fatty acids in the shirts worn by the older subjects, and think that the 2-nonenal comes from the breakdown of these fatty acid chains. The reason the fatty acids increase with age, meanwhile, is still unclear. The researchers speculate that it might be because of age-related changes to metabolism or changes in the amount of some other chemical in skin secretions.

Another big question still hanging in the air is what purpose, if any, an age-related change in smell serves. Humans and some non-human animals can tell the difference between older and younger individuals by smell, and some animals are known to be more attracted to the odor of older individuals and have more success mating as they age. One possible explanation for this is that older individuals may have some genetic advantage that allowed them to survive longer and makes them more attractive mates, and that distinct age-related odor is an advertisement for their genetic quality. It’s not clear that this is what actually happens, but if it is, it’s hard to imagine smell having much of an effect with humans when we place such high value on the physical attractiveness and other qualities of youth.

The fact that old person smell is usually thought of as unpleasant doesn’t seem to be a stumbling block here, though. Research subjects who didn’t know the source of the smell rated old person odors as less intense and less unpleasant than odors from younger people—suggesting that the smell on its own isn’t bad, but is perceived that way in certain contexts.

What's the Difference Between Cement and Concrete?

Vladimir Kokorin/iStock via Getty Images
Vladimir Kokorin/iStock via Getty Images

Picture yourself walking down a city block. The sidewalk you follow may be obscured by shuffling feet and discarded gum, but it’s clearly made from something hard, smooth, and gray. What may be less clear is the proper name for that material: Is it concrete or cement? Is there even a real difference between the two words?

Though they’re often used interchangeably, concrete and cement describe different yet related elements of the blocks, flooring, and walls that make up many everyday structures. In simple terms, concrete is the name of the gray, gritty building material used in construction, and cement is an ingredient used in concrete.

Cement is a dry powder mixture that looks much different from the wet stuff poured out of so-called cement trucks. It’s made from minerals that have been crushed up and mixed together. Exactly what kind of minerals it’s made from varies: Limestone and clay are commonly used today, but anything from seashells to volcanic ash is suitable. After the ingredients are mixed together the first time, they’re fired in a kiln at 2642°F to form strong new compounds, then cooled, crushed, and combined again.

Cement
Cement
lior2/iStock via Getty Images

This mixture is useless on its own. Before it’s ready to be used in construction projects, the cement must be mixed with water and an aggregate, such as sand, to form a moldable paste. This substance is known as concrete. It fills whatever mold it’s poured into and quickly hardens into a solid, rock-like form, which is partly why it’s become the most widely-used building material on Earth.

So whether you’re etching your initials into a wet sidewalk slab, power-hosing your back patio, or admiring some Brutalist architecture, you’re dealing with concrete. But if you ever happen to be handling a chalky gray powder that hasn’t been mixed with water, cement is the correct label to use.

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Why Do You Stop Feeling Tired As Soon As You Climb Into Bed?

tommaso79/iStock via Getty Images
tommaso79/iStock via Getty Images

There are few situations more frustrating: After a day spent nodding off at your desk, on the train, and on your couch, you suddenly can't sleep the moment you crawl into bed. It's not that you aren't tired or have insomnia, necessarily. Like a curse designed just to torture you, the sleeplessness only seems to occur when you're in your own bed at home, a.k.a. the place where you'd prefer to do your sleeping.

This maddening problem isn't in your head. According to TIME, many people have more trouble falling asleep in their own beds than they do elsewhere thanks to a phenomenon called learned or conditioned arousal. Conditioned arousal develops when you inadvertently train your body to associate your bed with being awake. In many cases, this results from doing stimulating activities in bed. For instance: If you like to slip under the covers and spend 40 minutes watching Netflix before closing your eyes, you're teaching your brain that your bed isn't for sleeping. That means the next time your head hits the pillow, your body will respond by preparing for the next episode of Friends instead of releasing the chemicals that help you fall asleep. The same goes for scrolling through apps, eating, and even reading in bed.

Doing things that aren't sleeping in bed isn't the only way to develop conditioned arousal. If there are other factors keeping you up at night—like thoughts about your day, or that cup of coffee you had at 8 p.m.—they can lead to the same result. Your brain starts to associate being in bed with tossing and turning all night, so even if those mental and physical stimulants go away, the muscle memory of being awake in bed remains.

Conditioned arousal is a vicious cycle that can't be broken in one night. The only way to manage it, according to the American Psychological Association (APA), is to minimize behaviors that contribute to poor sleep habits and to reserve your bed for sleeping (though sex is OK, according to the APA).

If you're a nighttime scroller, browse apps in a different room before getting into bed, or skip checking your phone at the end of the day altogether. When you spend more than 20 minutes struggling to fall asleep in bed, get up and move to a different part of the house until you get sleepy again; this will stop your brain from strengthening the association between your bed and feeling restless. The results won't be instant, but by sticking to a new sleep routine, you should eventually train your body to follow healthier patterns.

Of course, combating conditioned arousal alone isn't always effective. In people with conditions like anxiety and insomnia, intrusive thoughts and genetic factors can prevent them from falling asleep even under ideal circumstances. In such cases, the help of a medical professional may be required to sleep more soundly.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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