Outside, horns blare as traffic chokes the streets. Pedestrians push past each other on the crowded sidewalks, and the sound of a jackhammer pierces the air.

Inside, the bustle sounds like a distant hum. People lounge in soft robes and slippers, nibble walnut bread, sip lemon-flavored water, and leaf through coffee-table picture books.

They're waiting to be led to a lavender-scented room to get an exotic treatment: a ginger rub, perhaps. Maybe an herbal hot-oil wrap. Or a hot salt scrub.

They've entered the world of the day spa in this case, Bliss in Manhattan's Soho.

In this turbulent era, it's no wonder the spa business is booming.

"People are going to day spas to find relief from stress and anxiety," said Hannelore Leavy, executive director of the Day Spa Association (DSA). "Day spas are the quick fix. You want to go in and come out feeling good and beautiful. And you do."

About 91 million people visited spas annually in the year 2000, with 64 percent of them going to day spas, according to a study commissioned by the International SPA Association (ISPAA).

"You can disappear for a few hours without going away," said Rachel Lederman, an advertising producer who goes to a day spa about once a week. "There's no phone, no worry. You just enjoy being pampered."

When Leavy got into the industry in 1990, the day spa was a little-known entity. Only about 70 facilities existed back then. The concept took off in the mid-1990s.

"Then it started to explode," she said.

So did business at resort spas. Between 1990 and 2000, the combined number of day and resort spas grew by 314 percent, according to the ISPAA. The entire spa industry is a $5 billion business.

Now there are about 6,000 day spas alone, according to the DSA.

"It's the largest segment of the industry right now," said Leavy. "The dollar stretches much further in the day spa." Clients spend an average of $100 per visit, not including tip, she said.

Those employed at day spas have also noticed the spurt in business.

"We're growing in leaps and bounds," said Ann Marie Cilmi, director of education at Bliss.

Exact figures documenting Bliss' boom weren't readily available, Cilmi said, but she attributes the growth in part to the increasingly packed schedules that most people have.

"People are having less free time for themselves," she said. "They're expected to keep pace with more. It's a place to really relax."

Bliss' heavenly "Enwrapture" treatment, for example, involves an herbal hot-oil massage followed by a 20-minute wrap in mylar paper the tinfoil-like material used in metallic balloons so the body absorbs the oils and sweats away the toxins.

"It's an escapist thing," said Jennifer McGeorge, 30, an actress and caterer in New York who occasionally books massage appointments. "It's the ultimate comfort."

Though the majority of day spa-goers are women 75 to 80 percent the male clientele has grown in the last five years to about 20 to 25 percent of the total.

Leavy said the changes modern women have undergone have contributed to the industry's boom.

"Spas used to be for the wealthy woman the common woman could not afford to go," she said. "Now you have women who are executives; they're looking to get away from the hustle and bustle of everyday life."

To compete with the day spa saturation, hair and nail salons have begun offering services like waxing, facials and massage.

But to qualify as a day spa, a facility must meet industry guidelines (listed on dayspaassociation.com): offering a variety of treatments like massage, facials and aromatherapy; providing showers, changing rooms and private treatment rooms; and obtaining a business license.

Though the day spa is relatively new, the concept is ancient. The word SPA comes from the Latin "salus per aquam," which means "health from water." It's also the name of a tiny Belgian village where Roman soldiers would soothe their battle-scarred bodies by soaking in the town's hot mineral-rich springs.

Other ancient civilizations used spa treatments for health and relaxation too.

"Cleopatra bathed in milk every day," Leavy said.