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A dog’s nose is thousands of times more sensitive than a human’s, and new research shows they can smell stress in our breath and sweat. Photo: Shutterstock

Dogs can smell stress in our breath and sweat, enabling them to calm PTSD and anxiety sufferers before debilitating attacks happen, researchers say

  • The canine nose has long been known for detecting physical ailments like cancer, but animal specialists have now found dogs can smell stress in breath and sweat
  • This means they can be trained to preemptively offer comfort to sufferers of psychological illnesses like PTSD, to prevent attacks and improve quality of life

On a walk and when I let her off the lead, my Labrador Jip will pick up a scent and she’s off, on the trail of something that none of my senses can detect, with an urgency I cannot understand.

Deborah Debes, a canine behaviour specialist with a certificate in pet psychology, who runs Hong Kong’s DogManGoWoof dog training service, explains why. Dogs have such a strong sense of smell, she says, that they can tell when we are coming home by smelling us before we have even set foot in the door.

A dog’s nose is thousands of times more sensitive than ours, Debes says, with up to 300 million scent receptors compared to a human’s 5 million to 6 million. The area of the canine brain related to the sense of smell is roughly 40 times bigger than a human’s.

Understanding the extent of a dog’s sense of smell – a superpower that has been harnessed to detect illicit drugs, ivory, weapons, missing people and bodies – drives the work of animal psychologist Dr Clara Wilson at Queen’s University Belfast, in Northern Ireland.

Animal psychologist Dr Clara Wilson with sniffer dog Leon. Photo: Queen’s University Belfast

She recently led a study on dogs’ ability to sniff out human stress and why and how this might be useful.

She works with “bio-detection dogs” that can smell human health conditions such as cancer, Parkinson’s disease or Covid-19.
Soot, one of the dogs Wilson works with. Photo: Queen’s University Belfast
Debes has direct experience with this. One of her clients had breast cancer, but had no idea until she realised her new rescue mongrel was continuously sniffing one of her breasts.

“Her rescue dog, in effect, rescued her too,” Debes says.

“Dogs can also smell when we are hurt and will attempt to lick the area to try to help with the healing process. My previous rescue mongrel did this when I broke my wrist and before I had gone to the hospital for an X-ray.”

The research highlights that dogs do not need visual or audio cues to pick up on human stress.
Dr Clara Wilson, animal psychologist at Queen’s University Belfast

Wilson’s team’s work suggests that dogs can identify psychological conditions as well as physiological ones, and are able to smell when a person is stressed from breath and sweat samples taken before and after a stress-inducing task.

Essentially, a person under acute stress experiences changes in the volatile organic compounds emanating from their breath and/or perspiration that dogs are able to detect.

In every test session, each dog was given one person’s relaxed and stressed samples, taken only four minutes apart. All of the dogs were able to correctly alert the researchers to each person’s stress sample.

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“The findings show that we, as humans, produce different smells through our sweat and breath when we are stressed, and dogs can tell this apart from our smell when relaxed – even if it is someone they do not know,” Wilson says.

“The research highlights that dogs do not need visual or audio cues to pick up on human stress.”

Debes says dogs pick up on the chemical signals from the odours our bodies emit.

Canine behaviour specialist Deborah Debes. Photo: Deborah Debes

It’s not just fear dogs can smell – what you were always told is true: they smell when you are afraid. They can also detect chemical signals when an epileptic person is about to have a seizure and can respond by barking a warning.

This, Debes says, “has the effect of increasing the confidence levels and overall well-being of those with seizures”.

Dogs can also detect when a diabetic’s blood sugar is out of whack. Diabetic alert dogs, says Wilson, “smell when an owner’s blood sugar levels rise or fall, and alert them to this with attention-seeking behaviours”.
Soot performs tasks as part of work with Wilson. Photo: Queen’s University Belfast
The results of Wilson’s study could be useful in training service dogs to detect anxiety and PTSD, or post-traumatic stress disorder.

“Knowing that there is a detectable odour component to stress may raise discussion into the value of scent-based training using samples from individuals in times of stress versus calm,” she says.

This would change things up a bit, Debes says. At the moment, service dogs for PTSD sufferers are trained to look for indicators that their owner is anxious, such as crying or self-harming. The dog responds by nestling up to the person, or even using their paws to block the individual from hitting themselves.

PTSD support dogs provide therapy, interacting with their owner before, during and after difficult incidents. Photo: Shutterstock

Understanding that dogs can smell stress, she says, means that current training for PTSD service dogs can potentially be improved on.

“For example, on scenting stress they can be taught to immediately nestle up to the human in a comforting way or even fetch the person’s medication in a bite-proof container rather than waiting for outward indications of stress.”

PTSD sufferers with service dogs, says Debes, experience an improvement in their mental well-being as they benefit from support during anxiety attacks, as well as a reduction in attacks on account of the constant and reassuring presence of a support dog.

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She explains the animal behaviour behind this.

“Dogs are protective towards their pack and non-judgmental when their human is struggling to cope with a situation.” Not all humans are like this, and it is this totally non-judgmental response from their support dog that helps sufferers gain confidence, and so “feel more social and open with others”.

A dog’s protective nature can benefit a PTSD sufferer when they are out and about as sometimes their PTSD may be triggered by not knowing what is around the next corner, Debes says. A dog can confirm there is no danger round that corner and prevent a panic attack.

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They can also help with nightmares, she says – something many PTSD sufferers are plagued with – as dogs can be trained to be alert to night-terror indicators, making their presence in the bedroom a reassuring comfort to help PTSD sufferers get to sleep.

As well as detecting PTSD attacks, seizures and illness, “our four-legged companions provide therapy by interacting with their humans before, during and after these incidents, improving the well-being of their owner”, she says.

Dogs really are man’s best friend.

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