Cari Hanrahan smiled at the mirror, tossed her head and watched her long brown hair float through the air. She had walked into the salon with shoulder-length hair; now her locks fell to the middle of her back. With a long evening dress for her high school prom, she had the tresses to match.

Once upon a time, women and girls generally walked out of beauty parlors with less hair on their heads. Now, Hanrahan is one of many embracing the fast-growing trend of hair extensions -- strands of natural or synthetic hair that are clipped, glued, sewn or woven to the natural mane.

For decades, black women have used hair extensions for length and convenience, and celebrities relied on them for instant glamour makeovers. Beyoncé, Jennifer Aniston and Britney Spears are repeat wearers; Jessica Simpson, Brandy and Paris Hilton have launched their own hair-extension brands.

In recent years, extensions have made their way into mainstream U.S. salons, where women use them to dress up for a special occasion or to create a hairstyle in a hurry. Men and women also use extensions to restore fullness to thinning hair and to replace hair loss from chemotherapy.

Hairstylist Salvatore Minardi of Madison, N.J., who lengthened Hanrahan's hair for her prom, said, "This is not just about having longer hair. We use extensions to put in highlights without using chemicals. Extensions can give you color, drama, excitement."

Hanrahan said, "This is my first hair extension. It's really a dramatic change, and I like it."

She had long hair for years, then cut it off and donated her hair to Locks of Love, the charity that replaces hair that children have lost due to illness.

"I really like having long hair again," Hanrahan said.

Hair extensions might cost hundreds or thousands of dollars, depending on the quality of the hair and the complexity of the process. Hanrahan got one of the faster, less expensive procedures: several rows of synthetic hair discretely clipped to her natural hair in a seamless cascade. It costs about $150, can be cut, combed and styled, and will last several weeks before being easily removed without damaging the natural hair, Minardi said.

"No longer does a woman have to live with short hair," Minardi said. "If she wants long hair, she can have it."

A lucrative business

Hair extensions are a fast-growing, multimillion-dollar-a-year business, said Ron Cardillo, general manager of Naples, Italy-based SO.CAP.USA, which processes and sells human hair from India, Pakistan and Eastern Europe and trains hairstylists to do extensions.

He estimated that fewer than 10 percent of the country's 370,000 barber shops and salons do extensions; his firm works with 10,000 of them. There is more customer demand for extensions than salons can fill, he said, adding that the hottest regions of the country include California, the New York/New Jersey metropolitan area and Florida.

"Most salons still don't understand how important this service is," Cardillo said. "A hairdresser who is certified for hair extensions can earn three times more than what they normally earn from any other salon service."

Kimberly Givens of Soultry Scissors in West Orange, N.J., demonstrated the Christina method of hairweaving on Natauya Humphrey, one of her assistant cosmetologists. First, Givens wove several strands of Humphrey's own hair into a weft that lies flat against the scalp; then she attached extensions to the weft with a thin surgical needle and delicate cord.

"You can cut and style and wash the hair, and keep it in for about eight weeks," Givens said.

Hair extensions are a more lucrative business opportunity for salons than the traditional wash, cut and blow-dry business, Givens said.

"I used to do nails, but you can make much more money doing hair," she said. "A good hairstylist can make $3,000 a week. And we are recession-proof, because people want to look and feel fabulous. They want what they see in the magazines and on the red carpet -- and those women on the red carpet all use hair extensions."

Toni Love, an African-American cosmetology educator in Alabama and author of the 2001 textbook "The World of Wigs, Weaves and Extensions," said hair extensions have been popular in the black community at least since the 1980s and exploded onto the mainstream in the late '90s. While chemical treatments will relax the tight curls of African-American hair, extensions create a hairdo that requires little maintenance. Love says: "Women are very busy these days, and many of us don't have the time to spend on our hair."

Love trains hair stylists, who have found extensions to be a more lucrative business than traditional trimming and styling. She said one of her students earns $500 for a 90-minute session in which human hair is woven to the base of the client's natural hair. "She can do six clients a day and earn $3,000 a day," Love said. By contrast, a stylist who charges $40 to cut hair might earn $120 in 90 scissors-wielding minutes, she added.

A major supplier of human hair is Lugo Hair Center, which imports human hair from Asia for sale in its shops in New York, Miami and Puerto Rico. "Years ago, it was mostly African-American women who wanted hair extensions. Now, it's everybody," manager Giovanni Lugo said. Enough hair for a full-head style costs $170 and up, depending on the texture, color, length and amount, he said.