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Wear Deodorant? You Have More Armpit Bacteria Than Antiperspirant Users

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In our quest to look and smell good, we apply all kinds of chemicals to our bodies every day without giving it a second thought. Some of those products, like antiperspirant and deodorant, are specifically designed to kill bacteria. But what kind of effect do they have on your bacterial ecosystem as a whole? It depends on the product, scientists say in a new paper published in PeerJ.

By now, you probably know that our bodies are full of—and covered with—bacteria and other microorganisms. The sum total of all of these microbes is known as the microbiome. The microbiome is really hot right now; it seems like every week we’re learning more about what’s in there, what it’s doing, and how it can change. Recent studies have shown that health of your microbiome is related to all kinds of surprising things, from socializing to obesity. But there’s still a lot we don’t know. 

To find out how hygiene habits can affect the armpit microbiome, a team of researchers recruited 17 participants and divided them into three groups: people who use deodorant, people who use antiperspirant (not the same thing), and people who used neither. The volunteers were then given an eight-day schedule. On the first day, participants would use whatever product they usually used. From days two through six, they wouldn’t use anything at all. On days seven and eight, everybody used antiperspirant. And twice a day, the researchers swabbed the subjects’ armpits to collect bacteria.

The scientists were right to divide the antiperspirant and deodorant users into two camps. Analysis of the study participants’ underarm swabs revealed some pretty big differences in the products’ microbial consequences. 

"We found that, on the first day, people using antiperspirant had fewer microbes in their samples than people who didn't use product at all—but there was a lot of variability, making it hard to draw firm conclusions," author Julie Horvath said in a press statement. "In addition, people who used deodorant actually often had more microbes—on average—than those who didn't use product."

The effects of antiperspirant and deodorant use or non-use were surprisingly speedy. By the third day of the study, day two without product, the armpit ecosystems of regular antiperspirant users had already begun to rebound. By the fifth day without deodorant or antiperspirant, the participants’ “armpit communities” (as the researchers called them) were all equally lively.

But things took another quick turn when all the study participants wore antiperspirant: “… we found very few microbes on any of the participants,” Horvath said in the press statement, “verifying that these products dramatically reduce microbial growth." 

This doesn't necessarily mean that you should chuck your deodorant or stock up on antiperspirant. Having more bacteria is not intrinsically good or bad. It depends on what those bacteria are, and their role in the overall ecosystem. 

The makeup of the study subjects’ microbiomes varied depending on their choice of armpit products. The researchers found not only different amounts of bacteria on the skin of each group, but also different species. 

"Using antiperspirant and deodorant completely rearranges the microbial ecosystem of your skin—what's living on us and in what amounts," Horvath continued in the press release. "And we have no idea what effect, if any, that has on our skin and on our health. Is it beneficial? Is it detrimental? We really don't know at this point. Those are questions that we're potentially interested in exploring."

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How Does Catnip Work?
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If you have a cat, you probably keep a supply of catnip at home. Many cats are irresistibly drawn to the herb, and respond excitedly to its scent, rubbing against it, rolling around on the floor, and otherwise going nuts. There are few things that can get felines quite as riled up as a whiff of catnip—not even the most delicious treats. But why does catnip, as opposed to any other plant, have such a profound effect on our feline friends?

Catnip, or Nepeta cataria, is a member of the mint family. It contains a compound called nepetalactone, which is what causes the characteristic catnip reaction. Contrary to what you might expect, the reaction isn’t pheromone related—even though pheromones are the smelly chemicals we usually associate with a change in behavior. While pheromones bind to a set of specialized receptors in what’s known as a vomeronasal organ, located in the roof of a cat's mouth (which is why they sometimes open their mouths to detect pheromones), nepetalactone binds to olfactory receptors at the olfactory epithelium, or the tissue that lines the mucus membranes inside a cat’s nose and is linked to smell.

Scientists know the basics of the chemical structure of nepetalactone, but how it causes excitement in cats is less clear. “We don’t know the full mechanisms of how the binding of these compounds to the receptors in the nose ultimately changes their behavior,” as Bruce Kornreich, associate director of the Cornell Feline Health Center, tells Mental Floss. Sadly, sticking a bunch of cats in an MRI machine with catnip and analyzing their brain activity isn’t really feasible, either from a practical or a financial standpoint, so it’s hard to determine which parts of a cat’s brain are reacting to the chemical as they frolic and play.

Though it may look like they’re getting high, catnip doesn’t appear to be harmful or addictive to cats. The euphoric period only lasts for a short time before cats become temporarily immune to its charms, meaning that it’s hard for them to overdo it.

“Cats do seem to limit themselves," Michael Topper, president of the American Veterinary Medical Association, tells Mental Floss. "Their stimulation lasts for about 10 minutes, then it sort of goes away.” While you may not want to turn your house into a greenhouse for catnip and let your feline friend run loose, it’s a useful way to keep indoor cats—whose environment isn’t always the most thrilling—stimulated and happy. (If you need proof of just how much cats love this herb, we suggest checking out Cats on Catnip, a new book of photography from professional cat photographer Andrew Martilla featuring dozens of images of cats playing around with catnip.)

That said, not all cats respond to catnip. According to Topper, an estimated 70 percent of cats react to catnip, and it appears to have a genetic basis. Topper compares it to the genetic variation that causes some individuals to smell asparagus pee while others don’t. Even if a cat will eventually love the smell of catnip, it doesn’t come out of the womb yearning for a sniff. Young kittens don’t show any behavioral response to it, and may not develop one until several months after birth [PDF].

But some researchers contend that more cats may respond to catnip than we actually realize. In one 2017 study, a group of researchers in Mexico examined how cats might subtly respond to catnip in ways that aren’t always as obvious as rolling around on the floor with their tongue hanging out. It found that 80 percent of cats responded to catnip in a passive way, showing decreased motor activity and sitting in the “sphinx” position, an indicator of a relaxed state.

There are also other plants that have similar effects on cats, some of which may appeal to a wider variety of felines than regular old catnip. In a 2017 study in the journal BMC Veterinary Research, researchers tested feline responses to not just catnip, but several other plants containing compounds similar in structure to nepetalactone, like valerian root, Tatarian honeysuckle, and silver vine. They found that 94 percent of cats responded to at least one of the plants, if not more than one. The majority of the cats that didn’t respond to catnip itself did respond to silver vine, suggesting that plant might be a potential alternative for cats that seem immune to catnip’s charms.

Despite the name, domestic cats aren’t the only species that love catnip. Many other feline species enjoy it, too, including lions and jaguars, though tigers are largely indifferent to it. The scent of the plant also attracts butterflies. (However, no matter what you’ve heard, humans can’t get high off it. When made into a tea, though, it reportedly has mild sedative effects.)

The reason Nepeta cataria releases nepetalactone doesn’t necessarily have to do with giving your cat a buzz. The fact that it gives cats that little charge of euphoria may be purely coincidental. The chemical is an insect repellant that the plant emits as a defense mechanism against pests like aphids. According to the American Chemical Society, nepetalactone attracts wasps and other insect predators that eat aphids, calling in protective reinforcements when the plant is in aphid-related distress. That it brings all the cats to the yard is just a side effect.

Because of this, catnip may have even more uses in the future beyond sending cats into a delighted frenzy. Rutgers University has spent more than a decade breeding a more potent version of catnip, called CR9, which produces more nepetalactone. It’s not just a matter of selling better cat toys; since catnip releases the compound to ward off insects, it’s also a great mosquito repellant, one that scientists hope can one day be adapted for human use. In that case, you might be as excited about catnip as your cat is.

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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A Baby's Cries Might Hint at What the Child Will Sound Like as an Adult
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Babies may be incapable of talking, but at just a few months old, they've already developed many of the characteristics that will one day make their speaking voice distinct. That's the takeaway from a new study, reported by The New York Times, in which a team of bioacoustic researchers found that you can tell what infants will sound like at age 5 by analyzing their cries.

For their study, published in the journal Biology Letters [PDF], the researchers recorded the voices of 15 French children 4 to 5 years old. They then compared the clips to the children's "mild discomfort cries" recorded when they were 2 to 5 months old. The results showed that a baby's voice can be used to predict 41 percent of the variances they will have in their vocal pitch at age 5.

Other studies have suggested that what our voices sound like when we're young is a strong indicator of what they will sound like later on—even after puberty changes our vocal cords. A boy's voice pitch at age 7 can predict up to 64 percent of the distinguishing features his voice will have as an adult.

The study authors write that many of these variances may develop before childhood, and potentially in utero: "These observations suggest that inter-individual differences in [voice pitch] arise early in life and are largely unaffected by puberty, and raise the possibility that [pitch] may even be determined before birth."

The most important markers that determine pitch are the length, size, and tension of our vocal folds. But those aren't the only determinants: Environmental factors like smoking, pollution, and climate can affect how our voices sound as well, though these changes are usually temporary.

[h/t The New York Times]

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