We animal lovers have long known that, no matter what life may bring — sickness, sadness, or radiant health — pets make us feel better. Numerous studies have documented astonishingly wide-ranging effects. Cat owners enjoy a 30 percent reduction in heart attack risk. Watching swimming fish lowers blood pressure. Stroking a dog boosts the immune system. Now researchers can explain the source of our companion animals’ healing powers: Our pets profoundly change the biochemistry of our brains.

Despairing, I lay down on the blanket that protects our car’s upholstery from our border collie’s dirty paws. As I inhaled Sally’s scent, calm washed over me. Within a half hour, the dizziness eased enough for me to drive.

I once faced a sickening defeat. After a day and a half of an intensive scuba class, diving too deep, too fast produced pressure in my ears, causing dizziness and nausea. I was forced to quit. Next, I realized I was too vertiginous to drive home.

“This is science that supports a truth the heart has always known,” Meg Olmert writes in her book “Made for Each Other,” a synthesis of more than 20 years of work on the biology of the human-animal bond. She singles out one neuropeptide: oxytocin, a brain chemical long known to promote maternal care in mammals.


Oxytocin levels rise in a mother’s brain as she goes into labor, and produces the contractions that deliver the baby. Once her infant is born, just the sight, smell, or thought of the baby is enough to trigger milk letdown (a fact that has caused many a new mother to ruin a blouse.) Humans have known for millennia that this affects animal mothers, too: Ancient Egyptian tomb art shows a kneeling man milking a cow with her calf tethered to her front leg.


But oxytocin’s powers are not, as once thought, limited to mothering or triggered only by labor. Nor is it confined to females, to mammals, or even to vertebrates. Even octopuses — who not only lack breasts, but die when their eggs hatch — have a form of oxytocin called cephalotocin.

Oxytocin causes a cascade of physiological changes. It can slow heart rate and breathing, quiet blood pressure and inhibit the production of stress hormones, creating a profound sense of calm, comfort, and focus. And these conditions are critical to forming close social relationships — whether with an infant, a mate, or unrelated individuals — including, importantly, individuals belonging to different species.

In a study published in Proceedings of the National Academy of Sciences last June, Japanese researchers sprayed either oxytocin or saline solution into the nostrils of dogs, who then reunited with their owners. The owners were told not to interact with their dogs, but those whose pets inhaled oxytocin found them impossible to ignore. Statistical analysis showed the oxytocin inhalers were far more likely to stare, sniff, lick, and paw at their people than those who had saline solution.

Oxytocin is not the only neurotransmitter companion animals call forth from our brains. South African researchers showed that when men and women stroked and spoke with their dogs, as well as doubling the people’s blood levels of oxytocin, the interaction boosted levels of beta endorphins — natural painkillers associated with “runners high” — and dopamine, known widely as the “reward” hormone. These neurochemicals, too, are essential to our sense of well-being. A later and larger study by University of Missouri scientists also documented that petting dogs caused a spike in people’s serotonin, the neurotransmitter that most antidepressants attempt to elevate.


So it’s no wonder that pet-assisted therapies help troubled children, people with autism, and those suffering from Post Traumatic Stress Disorder and drug addiction. Pets help normalize brain chemistry.

“By showing how interacting with pets actually works,” says the Missouri study’s lead author, Dr. Rebecca Johnson, “we can help animal-assisted therapy become a medically accepted intervention” — one that could be prescribed like medicine and reimbursed by insurance.

All animals appear to have cells directly under the skin that activate oxytocin in the brain. So gentle touch — from grooming your horse’s coat to making love with your spouse — is a powerful trigger. But so is simply thinking about someone you love, whether it’s a person or a pet. And in fact, a small study published this fall at Massachusetts General Hospital found that MRI scans of women’s brains lit up in the same areas when shown pictures of their pets as when shown pictures of their children.

But here’s the best part: It’s mutual. We effect the same physiological changes in our pets as they do in us. As I lay on that blanket in our car, soothed by Sally’s scent, I remembered how my best human friend, Liz Thomas — whose column you will read next week — once quelled desperation and fear in another border collie named Tess, Sally’s beloved predecessor. I was away tending to my dying mother when Tess, a rescue with separation anxiety, suffered a stroke-like illness. For the first time in her life, she was confined overnight at the vet’s. Liz knew just how to help. She came to our house, retrieved my barn coat, and took it to Tess’s hospital cage. Tess inhaled my scent and instantly, her ears folded and the terror fell from her face. She let out a sigh and relaxed.


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Sy Montgomery is a naturalist and the author of more than a dozen books including the bestseller “The Good Good Pig.” She can be reached at syandlizletters@gmail.com.