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Did you know that dogs can tell when you're stressed out? But how do they know? Turns out they can smell it! Join Hank for a new episode of SciShow and learn all about it!
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Head to to learn more and for a 14-day free trial of their new Starter Plan. [♪ INTRO] Today, we’re talking about everyone’s favorite topic: stress. Fortunately, we are also going to be talking about dogs.

Because research published this week in the journal PLOS ONE has found that dogs can smell human stress. Which is an important clue to what makes our canine friends such good companions, as well as how they can provide support to people with anxiety- and stress-related conditions. Now, if you’re a dog owner, you might be thinking to yourself, yeah, of course my dog knows when I’m stressed!

That’s why I have a dog! And there is research showing that dogs can mirror our emotions: dogs and their humans have similar long-term levels of cortisol, the main stress hormone. But believe it or not, scientists are not sure how dogs are detecting our stress.

Some studies have asked dogs to smell people in different emotional states, like happy and fearful. But those studies didn’t really provide the “how”. So in order to measure whether the dogs can actually smell stress, these researchers wanted to develop a controlled experiment where the dogs would have to pick between odors, and where the owners weren’t in the room to read cues from.

So, after the human participants gave baseline sweat and saliva samples, they were asked to do some math. They had to count backwards from 9000 by 17s without pen and paper. And just to make sure they were good and stressed out, there were two researchers supervising who said scary things like, “It’s very important that you perform the task as quickly and efficiently as possible.” After the math, participants were asked to give sweat and saliva samples again.

Their samples were only used if they rated their stress at least two points higher on a scale from 1 to 10 than when they had started the test. Then, it was time to see what the dogs could do. There were four canine participants, named Treo, Winnie, Fingal, and Soot.

The names weren’t important to the study, but I thought that you should know. Because they’re good dogs. In the experiment, the dog was always given three options to sniff.

For the first phase, those options were “stressed human” and two blank samples. But, after ten trials learning the smell of stressed human, everything was wiped clean. The dogs got three new options: the stressed participant again, the same person when not stressed, and a blank control.

And in 94% of trials, the dogs got it right. In 720 sniff tests of 36 people’s sweat and saliva, these four dogs could reliably tell the difference between the smell of a person who was sitting around and the stench of a person who had just done a bunch of math. Now, the study was designed to try to avoid potential confounds.

For instance, the people the dogs were sniffing were not in the room to give visible or audible cues. The experiment was also double-blinded, meaning that the researcher working with the dog didn’t know the right answer either: there was another researcher behind a curtain who would signal when the dog got it right and should be rewarded. However, the study doesn’t necessarily mean that the dogs knew it was stress that they were smelling.

The task was already something the dogs had been trained on, so they were just excited to be good dogs and do their jobs and get rewards. They didn’t respond to the stress-stink by becoming stressed themselves. But it does show that dogs can tell stressed people-stink from normal people-stink, which means that it might be how they do it IRL.

The authors say this might help us train service dogs for things like anxiety and PTSD. Now that we know that they are detecting smell, specifically, that could help us teach them what to respond to, and make them better partners. And speaking of stress… if you feel like the pandemic has left you overall grouchier than you used to be, you may not be alone.

Researchers publishing this week in the journal PLOS ONE were looking to see whether the COVID-19 pandemic caused shifts in people’s personalities. And not only did they find evidence of that shift, but it was bigger than they expected. Now, it’s important to say what we mean when we talk about your personality.

This is a whole field of psychology with a long and complicated history, but generally, we’re talking about someone’s major psychological patterns and how they unfold across a lifetime. No test can wrap your personality up in a neat little bow, but the five-factor model of personality used in this paper is well-studied. It looks at: openness to experience, extroversion, and agreeableness, or how likely you are to be trusting and straightforward.

It also considers conscientiousness, which is your likelihood of being responsible, organized, and disciplined, and neuroticism, which is a tendency to experience negative emotions and be vulnerable to stress. Previous studies have shown that while personal stressful events absolutely cause change to someone’s Big Five personality factors, collective events and natural disasters don’t tend to bring about widespread change in who we are. But these researchers thought the COVID-19 pandemic was big enough and global enough that it just might.

Conveniently for the researchers, a longitudinal study of changes in the Big Five had been started in 2014, giving them a large pool of people to analyze – over 7,000! Everyone had been assessed at least once before and at least once during the pandemic. The survey asked about age, gender, education, and ethnicity, but did not fully account for race.

The researchers looked first at 2020, starting in March. For no particular reason. That year, they found that neuroticism decreased, which matches up with other reports that a lot of people felt less anxious and stressed early on.

And for the other four traits, there wasn’t a difference in 2020. But 2021 and 2022 were a different story. The decrease in neuroticism went away, and extroversion, openness, conscientiousness, and agreeableness all declined.

The effect was even /more/ dramatic when the participants were divided into three age groups. Middle-aged and older adults continued to experience less neuroticism in 2021 and 2022, but younger adults under 30 had a significant increase in it compared to before the pandemic. Younger adults also showed a more dramatic decline in agreeableness and conscientiousness during that time.

Now, it’s important to note that these effects were… pretty small. They only added up to one-tenth of a standard deviation’s worth of change. Which is a little hard to picture, but that’s how these things get measured.

The takeaway is: that’s how much change we might normally expect to see in someone’s personality across ten years. So, it’s definitely not nothing. And, look, the authors are clear that it might not just be the pandemic.

Any number of major social events in the last few years could have been significant stressors, and it’s not like that’s a short list. The authors also don’t know if these changes are here to stay, or if we could see reversals again in a couple of years. But if you have felt like the pandemic has changed you in some ways?

You may not be alone in that. There are so many things to be stressed about during the COVID-19 pandemic, but figuring out how to sell products from your business should not be one of them. That’s where Shopify’s Starter Plan can help.

Shopify is an e-commerce platform, which means they make it easy for you to sell cool stuff. I’ve been using Shopify for over ten years at, which is like our main store, and a bunch of other ones including where you can get calendars from SciShow. But what they did not have when I started was a 5 dollar per month starter plan to get you going fast.

With the Shopify Starter Plan, you just need an image and a product description. You’ll be ready to sell whatever you’re selling after just a few clicks. Then you can share your professional-looking online store on pretty much every social media, including TikTok, Instagram, and Snapchat.

For a 14-day free trial of Shopify’s new Starter Plan, you can head to Thank you to Shopify for supporting this SciShow News video and thanks to you for watching! [♪ OUTRO]