Perrie Susman devotes plenty of time to picking the perfect Halloween costume. In previous years, she’s opted for skeleton, frog and cow outfits. This Halloween, she’s going with a Headless Horseman theme, she says.

But Susman, a rehabilitation aide in West Palm Beach, Fla., is not talking about the outfit she herself will wear on Oct. 31. Instead, she’s referring to the costume she’s purchased for Domino, her five-year-old Lab-pit bull mix.

“I do it because I like to dress up and I like to have somebody to dress up with,” says Susman.

Yes, Halloween has gone to the dogs. And the cats, too. Sales of pet costumes have soared in recent years, growing by 68% — from $220 million in 2010 to $370 in 2012, according to the National Retail Federation. And individual retailers say they see demand only increasing in the years ahead. PetSmart points to the fact that it now carries 111 styles of pet costumes and accessories; it’s even starting to offer items for “small animals.”

“If you don’t have a cat or dog, you can still dress up your guinea pig,” says Dara Foster, resident pet-fashion stylist for PetSmart.

The trend has gotten so big that a number of communities are hosting pets-in-costume parades or gatherings. Already for several years now, in New York’s Tompkins Square Park, hundreds of pet lovers have gathered for a dog parade, replete with “Best in Show” costume honors.

What’s behind the boom? In many ways, it speaks to America’s growing fascination with Halloween, which has gone from being a kid-centric event to almost a mini-Christmas, with all the attendant decorating, dressing up and partying. Per-person spending on Halloween has increased 55% since 2005 — from $49 to $75 — according to the National Retail Federation. And pop-up Halloween stores have become a common sight in many malls and shopping thoroughfares.

The fascination with Halloween dovetails with our passion for pets. “Your pet is now seen as an extension of your family. And you’re going to spend on that pet like you spend on your son and daughter,” says National Retail Federation spokesperson Kathy Grannis. Indeed, pet products and services now constitute a $53 billion industry, up by 5% in the past year alone, according to the American Pet Products Association, a trade organization.

There may be another factor at play in the popularity of pet costumes: They’re a lot cheaper than the human variety. Packaged ones can generally be found for under $20 — and in some cases, under $10. By contrast, adult costumes can easily run in the three or four figures — or even higher.

PetSmart

In other words, it’s a cheap but effective gag. “Let’s face it: Pets in costumes are funny,” says Sara Gaugl, director of marketing with Savers Thrift Stores, which also carries a large selection of costumes for the animal set. Gaugl adds that the company has already sold about 40% of its stock of pet costumes and it hasn’t hit its busiest shopping time for Halloween.

Still, before you buy Fido that Headless Horseman costume, experts say it’s worth keeping a few safety and other considerations in mind. For starters, not all animals are going to be receptive to the idea — and it makes little sense to force the issue. “It’s probably no good dressing up a dog that’s jumping around,” says Dr. Jules Benson, vice president of veterinary services for Petplan Pet Insurance. But even if the pet is willing, it’s important to make sure the costume is loose enough to avoid the risk of choking or chafing, Benson adds.

And don’t forget that other important consideration, “protecting your pet’s dignity,” says Benson with a laugh. But a lot of people say their pets take pleasure in getting dressed up — or at least in getting the attention that results from donning a costume. Certainly, that’s what Perrie Susman has noted when it comes to Domino. As soon as the dog is out the door come Halloween night, “his little tail starts wagging,” Susman says.