The Scent of Emo­tions

Dogs can smell your emo­tional state—and it al­ters their mood


Dogs can smell your emo­tional state—and it al­ters their mood.

Ire­mem­ber once lis­ten­ing to a lec­ture de­liv­ered by a clin­i­cal psy­chol­o­gist about how to cure a per­son’s fear of dogs (tech­ni­cally called cyno­pho­bia). Dur­ing the ques­tion pe­riod that fol­lowed, a per­son from the au­di­ence asked, “Isn’t treat­ing a fear of dogs com­pli­cated by the pho­bic per­son’s re­ac­tion to dogs? It’s my un­der­stand­ing that dogs can ‘smell fear’ on a per­son, and the scent trig­gers an ag­gres­sive re­sponse in the dog. If so, the in­di­vid­ual’s pho­bia would be strength­ened be­cause their fear­ful scent would gen­er­ate a hos­tile re­sponse in any dog they en­coun­tered.”

The psy­chol­o­gist re­sponded by not­ing that she had also often heard of dogs de­tect­ing and re­spond­ing to the emo­tional scent pro­duced by peo­ple, how­ever, she knew of no di­rect data. As far as she could tell, it might just be a pop­u­lar myth.

There is a lot of ev­i­dence which sug­gests that dogs are good at read­ing hu­man emo­tions. For ex­am­ple, dogs can read the fa­cial ex­pres­sions of peo­ple. Re­search has shown that they re­spond dif­fer­ently to happy ver­sus an­gry fa­cial ex­pres­sions, not only from live peo­ple, but also from pho­to­graphs. Dogs do not sim­ply read these fa­cial ex­pres­sions but re­act, chang­ing their re­sponses to in­di­vid­u­als and the things in their en­vi­ron­ment based on these ex­pres­sions. Thus an an­gry glare that their owner di­rects to­ward some­one will cause the dog to avoid that per­son in the fu­ture.

There is also ev­i­dence that dogs can read our tone of voice and ex­tract our emo­tional state from that. If, for in­stance, their owner looks at some­thing and says some­thing like, “Wow! That is re­ally nice!” in a happy tone of voice, the dog is much more likely to ap­proach that thing.

All of these stud­ies, how­ever, fo­cused on the dog rec­og­niz­ing vis­ual and au­di­tory cues for emo­tion trans­mit­ted by peo­ple; the con­tri­bu­tion of a dog’s ex­quis­ite abil­ity to rec­og­nize scent has only barely been in­ves­ti­gated in this re­gard. It makes sense to think that a per­son’s emo­tional state may al­ter how they might smell to a dog. This is be­cause our emo­tions can trig­ger pheromones, which are bi­o­log­i­cal chem­i­cals that al­ter the com­po­si­tion of bod­ily flu­ids—such as our sweat, which then evap­o­rates into the air around us. In essence then, we are mov­ing in a lo­cal­ized cloud of smells which con­tains in­for­ma­tion about the emo­tions that we are cur­rently ex­pe­ri­enc­ing.

There was one, some­what odd, piece of re­search, which sug­gests that dogs do

We are mov­ing in a lo­cal­ized cloud of smells which con­tains in­for­ma­tion about the emo­tions that we are cur­rently ex­pe­ri­enc­ing.

process and rec­og­nize some emo­tional smells. This study was con­ducted by a team of re­searchers headed by Mar­cello Sinis­calchi from the Uni­ver­sity of Bari “Aldo Moro” in Valen­zano, Italy. In that in­ves­ti­ga­tion dogs were pre­sented with a small vial which re­leased minute amounts of a chem­i­cal smell. The vial was small enough so that if the dog wanted to sniff at it he could use only one nos­tril at a time. Some of the smells tested were neu­tral (such as the scent of le­mon), while oth­ers were pos­i­tive (dog kib­ble), how­ever one of the vials con­tained adren­a­line, a stress hor­mone present in pheromones when an in­di­vid­ual is suf­fer­ing from fear or anxiety. What these re­searchers found was that the dogs were much more likely to use their right nos­tril when sniff­ing the adren­a­line. I know that some read­ers are now think­ing, “So what?” but bear with me; this is an im­por­tant find­ing for two rea­sons: First, that the dogs re­spond dif­fer­ently when sniff­ing adren­a­line shows that dogs can rec­og­nize the scent of a stress hor­mone. The sec­ond rea­son that this par­tic­u­lar be­hav­iour makes sense is be­cause the right nos­tril leads di­rectly to the right hemi­sphere of the brain which is be­lieved to be more spe­cial­ized for pro­cess­ing emo­tional stim­uli than the left hemi­sphere of the brain.

The ques­tion about whether dogs can smell pos­i­tive ver­sus neg­a­tive emo­tional states, and, specif­i­cally, how dogs might be­haviourally re­spond to such scents has re­cently been ad­dressed by another Ital­ian re­search team, this one headed by neu­ro­bi­ol­o­gist Bi­a­gio D’Aniello of the Uni­ver­sity of Naples “Fed­erico II.” The re­sults were pub­lished in the jour­nal An­i­mal Cog­ni­tion. The re­searchers say that their study “was de­signed to ex­am­ine a new per­spec­tive, namely the trans­mis­sion of emo­tional states from hu­mans to dogs via hu­man body odours pro­duced dur­ing hap­pi­ness and fear.” They were also very con­cerned about test­ing the pop­u­lar no­tion that if dogs smell fear on a per­son it is likely to trig­ger an ag­gres­sive re­sponse from the dog to­ward the fear­ful in­di­vid­ual.

The first step in a piece of re­search like this in­volves gath­er­ing the scent stim­uli. The “odour donors” came from a lab­o­ra­tory in Lis­bon. A num­ber of peo­ple were shown a 25 minute video de­signed to in­duce the emo­tional states of ei­ther fear or hap­pi­ness. Sweat sam­ples were then col­lected on pads, placed in sealed pack­ets, frozen, and re­turned to the be­havioural lab in Naples.

The test sub­jects were a sam­ple of 40 Labrador and Golden Retriev­ers who had been fit­ted out with mo­bile heart rate mon­i­tors. Each dog was placed in a small room with his owner and a stranger (who was not one of the odour donors). Both the dog’s owner and the stranger sat read­ing mag­a­zines and did not specif­i­cally in­ter­act with the dog. Mean­while an ap­pa­ra­tus was used to dis­perse scents from ei­ther the “happy sweat” or the “fear­ful sweat,” while in a con­trol con­di­tion no odour was re­leased.

The dogs’ be­hav­iours and phys­i­o­log­i­cal re­sponses did change as a re­sult of their ex­po­sure to emo­tion­ally tinged sweat odours. The dogs that had been ex­posed to the fear-related smells showed more be­havioural signs of stress than those ex­posed to the happy or neu­tral smells. These dogs seemed to also seek re­as­sur­ance through con­tact with their own­ers. In ad­di­tion, when the fear smell was in the room the dogs’ heart rates were con­sid­er­ably higher than they were in ei­ther the happy or neu­tral con­di­tions.

How­ever, while the dogs were clearly re­spond­ing emo­tion­ally to the scent of fear, their re­sponse seemed to mir­ror the emo­tion that they were de­tect­ing in that they acted in a fear­ful man­ner them­selves. There was no ev­i­dence of ag­gres­sion to­ward ei­ther the owner, the stranger, or the scent dis­pens­ing ap­pa­ra­tus.

The dogs also seemed to rec­og­nize the odour as­so­ci­ated with a happy emo­tion. Ex­po­sure to that scent did not pro­duce stress signs or an el­e­vated heart rate, but rather the dogs now tended to show more in­ter­est and ap­proach be­hav­iour to­ward the stranger.

In an in­ter­view, D’Aniello sum­ma­rized the re­sults say­ing, “Thus our data, while sup­port­ing the dog’s abil­ity to per­ceive hu­man emo­tional chemo-mes­sages, do not prove that they trig­ger at­tack.” As for the sug­ges­tion that some­one who is afraid of dogs is more likely to be the re­cip­i­ent of hos­tile re­sponses when they meet dogs, he sug­gested, “When peo­ple are afraid of dogs, they also as­sume un­usual pos­tures and look the dog in the eyes. This be­hav­iour can be in­ter­preted by the dog as a threat.”

Bot­tom line? Dogs do seem to be able to smell hu­man’s emo­tional state and look to their own­ers to model their re­sponse. As for those fear­ful of dogs? The scent of your fear alone is un­likely to pro­voke a re­sponse, though your un­usual fear-driven be­hav­iour might well make a dog un­com­fort­able.

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