Move over, kids. Halloween is for grownups

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(CNN) -- It was once dominated by children, but today Halloween is a decidedly adult affair -- replete with raucous parties, naughty get-ups and expensive ornamentation.

An estimated 71.5% of Americans are planning to celebrate Halloween this year, up from 52.5% in 2005, according to the country's National Retail Federation (NRF)

"A large portion of the growth is coming directly from adults who begin celebrating as early as a month prior to Halloween night," says NRF spokeswoman Kathy Grannis. "We are definitely seeing that it is no longer only a children's holiday."

The trend is going global, too. Within the last five years the holiday has grown considerably outside of the U.S., according to Lisa Morton, author of "The Halloween Encyclopedia" and "Trick or Treat?: A History of Halloween."

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In Great Britain, "there's been an almost 700% increase in adult costume sales since 2009," she says. It's also growing in Japan, where costume play has a longstanding tradition.

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All grown up

The shift from children's to adult holiday can be traced to the 1970s, when Halloween street festivals in several gay neighborhoods in the U.S. began to transform into adult parties featuring lavish and over-the-top costumes.

In the mid-1980s, Halloween gained even more traction among adults, helped by the Coors Brewing Company, who ran an ad campaign featuring TV horror host Elvira. According to Morton, the marketing ploy helped make the ghoulish night a "beer holiday" in the mold of Superbowl Sunday and St. Patrick's Day.

Retailers capitalized on the party mood and responded to the demand for theatrical dress up. Pin-up pirate, naughty nurse, even sexy Big Bird -- you name it, and there's a sultry version of the costume available today.

Skimpy Halloween get-ups have been available for as long as costumes have been sold commercially, but in the last decade the prevalence of sexy costumes has really exploded, according to Lesley Bannatyne, author of "Halloween Nation: Behind the Scenes of America's Fright Night."

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Why the desire to flaunt so much skin during this particular celebration, which falls at a time of year when temperatures in the northern hemisphere take a downward turn?

"Whatever box you're in, Halloween is when you get out of it, and for some, sexiness or outrageousness is their expression of getting out of it," Bannatyne says.

Halloween also benefits from being seen as a secular celebration, open to all and flexible enough to adapt to the prevailing cultural current, she adds.

Scaring up big business

What folklorists say began as ancient pagan festival celebrating the Celtic New Year, has today evolved into a multibillion-dollar commercial opportunity.

The NRF estimates Halloween spending in the U.S. alone will hit a record $8 billion this year, with the average U.S. consumer expected to shell out $80 on costumes, candy and decorations.

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In the UK, Planet Retail forecasts Halloween sales will reach nearly $549 million, up 12% from 2011. Adults are helping drive that rise.

"In the last few years, there have been more adult parties going on at the weekend and it has become more of a big event," says Nicole Parker-Hodds, an associate analyst at Planet Retail.

Halloween is a holiday that morphs with the times, says Morton: "It goes through cycles and changes its identity about every 40 years."

Its reincarnation as a commercial fun fest for adults may be fleeting, but for now, business keeps booming.