This is one scientific study that passes the sniff test.

A dog’s nose knows, almost always, when its humans are experiencing stress, according to UK researchers.

A recent study from Queen’s University Belfast suggests dogs can smell the difference in breath and sweat from people who are suffering the negative emotion with an accuracy of 93.75 per cent.

“This study demonstrates that dogs can discriminate* between the breath and sweat taken from humans before and after a stress-inducing* task,” said School of Psychology* PhD candidate and study author Clara Wilson.

“This finding tells us that an acute*, negative, psychological stress response alters the odour profile of our breath (and) sweat, and that dogs are able to detect this change in odour,” Ms Wilson said.

To test the theory, researchers collected samples of breath and sweat from people both before and after a fast-paced, complex maths problem.

They collected heart rate, blood pressure, and self-reported stress level measurements in the study, published in the peer-reviewed journal PLOS ONE.

Within three hours of collection, breath and sweat samples from 36 participants who reported stress were presented to four trained dogs of different and mixed breeds.

The animals detected stress in 675 of 720 trials, or 93.75 per cent of the time on average. Individual dogs ranged in performance from 90 per cent to 96.88 per cent accuracy.

The four dogs were aged between 11 to 36 months and included a male cocker spaniel, a female cockapoo, and two undetermined mixed breed rescue dogs similar to a lurcher and a terrier.

Ms Wilson and her colleagues believe the dogs, with their remarkable sense of smell and coevolution* with humans, can detect odours that show a change in “volatile organic compounds*” produced in response to stress.

The results suggest how hounds are able to support human psychological conditions such as anxiety*, panic attacks and post-traumatic stress disorder* (PTSD).

“Dogs were able to discriminate, with a high degree of accuracy, between human breath and sweat samples taken at baseline* and when experiencing psychological stress,” the study states.

“Establishing that dogs can detect an odour associated with stress sheds light on the human-dog relationship and adds to our understanding of how dogs may interpret, and interact with, human psychological states.”


  • discriminate: recognising difference, being able to distinguish between one thing and another
  • stress-inducing: conditions that bring about, prompt or give rise to stress
  • psychology: scientific study of the mind and behaviour
  • acute: very serious, extreme or severe
  • coevolution: evolutionary changes in two species that occur in a reciprocal way
  • volatile organic compounds: organic chemicals that are released into the air
  • anxiety: the body’s physical reaction to threat or perceived threat, including worried thoughts and pounding heart, tummy butterflies and rapid breathing
  • post-traumatic stress disorder: a set of reactions that can develop when someone has been through a terrible event
  • baseline: reasonable and defined starting point for comparison purposes, like a resting position


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  1. Dogs could smell the difference in people after stressful tasks using what two measures?
  2. The dogs detected stress in how many of a total of 720 trials?
  3. How many people and dogs were involved in the study?
  4. What dog breeds were used in the study?
  5. What was the range of accuracy for the performance of individual dogs?


1. Shorter, simpler
Rewrite this story in under 50 words. To do this, you may need to leave out precise facts and figures from the study and make more generalised statements about the results instead. Don’t forget to include a headline!

Time: allow 20 minutes to complete this activity
Curriculum Links: English

2. Extension
Write a persuasive paragraph to either support or refute the following statement:

“Dogs’ ability to detect stress in humans makes them an ideal classroom pet.”

Time: allow 15 minutes to complete this activity
Curriculum Links: English

Stretch your sentence
Find a “who” in the cartoon – a person or an animal. Write it down.

Add three adjectives to describe them better.

Now add a verb to your list. What are they doing?

Add an adverb about how they are doing the action.

Using all the words listed, create one descriptive sentence.

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