Maddison Tischler, a consultant at the Denver airport, greets Nelson, a therapy dog. (Cyrus McCrimmon/Denver Post)

Steve Cearley and his dog Shanti made their way down the airport concourse in matching blue plaid vests, prompting travelers to glance up from their computers and cellphones. After two airport employees stopped to fuss over Shanti, an 88-pound Great Pyrenees with long, white fur, Cearley, a full service dog handler, passed around a lint brush.

When “you’re petting a dog, you’re not thinking about other stresses,” Cearley said with a smile. “Like whether your plane is late.’’

With the holiday travel season in full swing, bitter complaints about the state of air travel in America fill the air like Christmas carols. On blogs and social media, passengers rant about canceled flights, long security lines, crowded terminals and appalling food.

So a growing number of airports are looking to lighten the psychological load, offering a comforting cadre of volunteers with wet noses, limpid eyes and wagging tails.

Last month, Denver International became the 31st airport in America to launch a “therapy dog” program, featuring a wide variety of hounds specially trained to interact with people. Operating on the theory that animals can help calm people in stressful situations, the pooches roam the concourses in their custom-made vests emblazoned with the words “Pet me.’’

Therapy dog "Ripey" walks the runway at the introduction. 17 of the 28 dogs were on hand to meet and greet travelers and employees offering a little stress relief. (Cyrus McCrimmon/DP)

“We’re always trying to improve the customer experience,’’ said Heidi Huebner, director of volunteers at Los Angeles International Airport, who keeps track of therapy dog programs at airports across the nation. “Travelers are not in a great place, and holding or petting a dog makes a difference in their day.’’

In Denver, the program is known as the Canine Airport Therapy Squad, or CATS. Since November, 28 registered therapy dogs have been roaming the airport with their owners, who are volunteers.

On a recent weekday, Michael Boyer sat cross-legged on the floor in the middle of a busy concourse and smiled as he petted a coffee-colored dog named Radar.

“I love dogs and I hate airports,’’ said Boyer, 29, who was waiting to catch a flight to Chicago.

Radar’s owner — who also wore a blue plaid vest — handed Boyer a trading card with a picture of the Belgian Malinois and interesting facts, such as his weight (68 pounds), favorite treat (pistachio nuts) and pet peeve (squirrels).

Nearby, an elderly couple petted Shanti. Her trading card listed her favorite treat as cheese and her pet peeve as “not being petted.’’

Airport therapy dog programs have become so popular that the American Humane Association recently released a guide for airports interested in implementing a program, said Amy McCullough, national director of humane research and therapy at the association. The guide cites studies done in hospitals, nursing homes and schools that show that petting a therapy dog can lower people’s blood pressure and reduce their stress and anxiety.

“A lot of the studies to date are somewhat anecdotal, but the field is growing in terms of research,’’ McCullough said.

The American Humane Association’s involvement in animal-assisted therapy dates to 1945, when therapy dogs aided soldiers recuperating in military hospitals. The concept arrived in airports after the 9/11 terrorist attacks when an interfaith chaplain volunteer brought her therapy dog to Mineta San José International Airport, hoping it would ease travelers’ anxieties.

Using the San José program as a model, Huebner started a therapy dog program in the Los Angeles airport in 2013 called Pets Unstressing Passengers, or PUP. Last year, Huebner spoke about the PUP program at a national airport conference, piquing the interest of people in Denver.

At the Denver airport, there were “many meetings and many hurdles to clear’’ before the CATS program could be launched, said Mark Inzana, manager of customer services initiatives at the airport.

“We have very high standards,’’ he said, noting that all of the dogs in the CATS program have at least one year of experience working as therapy animals at hospitals, schools, libraries or hospices.

The CATS team is made up of 14 breeds, including German shepherds, golden retrievers and a St. Bernard. The largest dog is a 160-pound Newfoundland; the smallest is an 11-pound Jack Russell terrier.

All of the dogs are registered and insured by the Alliance of Therapy Dogs, which requires each dog to be in control and have good manners — “no aggression or excessive licking, jumping or pawing,” said Billie Smith, executive director of the organization, which is based in Cheyenne, Wyo.

“Everything is so unpredictable at an airport. There are a lot of fast-moving things, chaos. That’s why we want dogs who are a little more seasoned,’’ Smith said.

Inzana said each therapy dog’s owner has to clear the airport’s many security checks, including fingerprinting. The owners are also trained as airport ambassadors so they can answer any other questions that might arise.

Inzana said he has been so pleased with the program that he hopes to expand it next year.

“I knew kids would like this, but I’ve really been surprised by how many adults and airline employees have benefited.’’ The dogs, he said, are “like furry magnets.’’

Finholm is a freelance writer.

American Dispatches is an occasional feature exploring people, trends and issues making news around the nation.