Dogs too could experience negative emotions, if they 'smell' stress in humans, a study, published in the Scientific Reports journal, has found.

It is known that the smell coming from a stressed person "subconsciously affects" the mental state of people around, including their emotions and choices.

The study's researchers, however, wanted to find out if dogs too were affected similarly in response to odours from a stressed human.

"Dog owners know how attuned their pets are to their emotions but here we show that even the odour of a stressed, unfamiliar human affects a dog's emotional state, perception of rewards and ability to learn," Nicola Rooney, a senior lecturer at the University of Bristol, UK, said.

"Working dog handlers often describe stress travelling down the lead, but we've also shown it can also travel through the air," Rooney, lead author of the study, said.

The team tested how a stressed human affected dogs' learning and emotional state, based on the theory that making 'optimistic' or 'pessimistic' choices indicate positive or negative emotions, respectively.

The authors recruited 18 dog-owner partners to participate in a series of trials involving treats, while being exposed to either no odours or those coming from sweat and breath samples of stressed or relaxed people.

For the trials, the dogs were trained such that a food bowl placed in one location contained a treat, whereas that placed in another location was empty.

Having learned the difference, the dogs were seen to become faster when approaching the food bowl with the treat, compared to when going towards the empty one.

Now, the researchers tested how quickly the dogs would approach "new, ambiguous" bowl locations positioned between the original two.

A swift, brisk approach towards the food bowl reflected 'optimism' of finding a treat and thereby, a "positive emotional state," according to the authors.

On the other hand, moving slowly towards the food bowl indicated 'pessimism' regarding finding a treat, thereby betraying the dog's negative emotions, they said.

The authors found that the smell of stress slowed down the dogs in approaching the food bowl placed in the new locations, suggesting they were pessimistic about finding a treat in it.

The dogs exposed to odours of relaxed people did not show this effect, the authors found.

They said that the 'pessimistic' response reflected the dog's negative emotional state and could be the dog's way of conserving energy and avoiding disappointment.

"Understanding how human stress affects dogs' wellbeing is an important consideration for dogs in kennels and when training companion dogs and dogs for working roles such as assistance dogs," Rooney said.

Except for the headline, this story has not been edited by The Telegraph Online staff and has been published from a syndicated feed.