On the crowded streets of the neighborhood, an increasing number of Orthodox Jewish women were seen wearing cloth head coverings, having left their wigs at home. Sarah Klein, a neighborhood resident, said that until the confusion was cleared up, she would leave the house only if she wore a baglike snood.

For thousands of Orthodox women, one of the most fundamental practices of daily life — adhering to the code of modesty that prohibits a public display of their hair after marriage — was thrown into turmoil this week by a ruling from a distant authority. More than 5,700 miles away in Israel, several rabbis issued a ban on wigs made in India from human hair, which is used to make many of the wigs sold in Brooklyn. The rabbis said the hair may have been used in Hindu religious ceremonies, which like other pantheistic practices are considered idolatrous in Orthodox teaching.

As a result, many of the women felt obliged to put aside their costly wigs, flocking instead to stores that sold acceptable replacements.

"You have to hope whatever you have is good, otherwise you put a thousand dollars in the garbage," said a woman named Mindy, who declined to give her last name for fear of what her father-in-law would think.

The commotion, like so many others that take place every day in New York's myriad enclaves, remained beneath the larger city's radar, but it was of profound importance to residents of neighborhoods like Borough Park, where news of a rabbinical ruling can spread like flame. Prohibitions against idolatry are based on Judaism's founding monotheistic beliefs, and echo strongly in homes where even portrait photographs are banned as graven images.

"The way Orthodox people live their lives is very complex to begin with," said Chaya Lewis, an administrative assistant at a school in Crown Heights. "We do everything everybody else does, yet we have guidelines. If this is a problem, we're going to find a way."

The modesty regulations have given rise to a thriving Brooklyn trade in wigs, along streets like 13th Avenue in Borough Park. Wigs of human hair are particularly prized, and can cost several thousand dollars. They not only look better, some women say, but they also last longer.

One of the most respected Jewish authorities in the ultra-Orthodox world, Rabbi Yosef Shalom Elyashiv, issued the Indian hair ban from Israel on Wednesday, prompting some people in Israel to create lists of stores selling banned wigs and to burn Indian wigs in bonfires, according to Ha'aretz, an Israeli newspaper.

Rabbi Elyashiv's ruling was posted on at least one Israeli news Web site, and word quickly circulated in Brooklyn. But the worry was not universal. Many communities, like the large Satmar community in Williamsburg, were awaiting their own rabbis' rulings.

The issue had come up several years ago, said Rabbi Yisroel Belsky, a leading authority on Jewish law for the Orthodox Union in the United States, but was resolved without a ban. He said it appeared that practices in the Hindu temples where the hair of Indian women is cut might have changed, prompting the new ruling.

He said he would study the matter and consider his own ruling, but for now stood by Rabbi Elyashiv's interpretation. One of the difficulties, he said, was discerning just what the Hindu hair-cutters had in their minds when they made their offerings, because that had a bearing on whether their acts were idolatrous.

Many women, rather than risk wearing Indian hair or out of confusion born of rumor, simply abandoned their human hair wigs.

Not Celine Schonberger, 19. She learned about the problem when her husband came back from his synagogue on Tuesday and asked if her wig was Indian or European. "He said I was not allowed to wear Indian," Mrs. Schonberger said. So she checked with her wig maker. "It's 100 percent fine," she said. Her mother got an O.K. from her own rabbi. An aunt bought a snood. "She couldn't go out with her wig," Mrs. Schonberger said.

Others in the neighborhood said teachers at a local girls school were now appearing in snoods. Meanwhile, wig manufacturers are sitting on huge inventories of merchandise; private makers are not even returning calls, for fear they may end up violating the rules. Some wig makers have advertised in a local Yiddish paper that their wig hair is not Indian, residents said.

At Yaffa's, business was bustling at 5 p.m. yesterday. "They emptied the shelves already for synthetic," said one saleswoman.

When the Uptown Girl Snood Factory Outlet in Borough Park opened at 11 a.m., a line was already at the door, said Michelle Aaron, the manager. "Thank God, today's been great," she said, noting that it was the second anniversary of her father's death. "He sent me a blessing," she said.

Mrs. Klein, 48, was picking out a new snood. She said she wanted to hear more from the rabbis before going back to her wigs. "I will be back in a wig once I know what the rulings are," she said. Fortunately, she said, she did not have to go to Manhattan yesterday wearing the headgear.

"I would look funny," she said. "One of the goals of modesty is to blend. When you wear a snood on the subway, you never blend."

The Demikini, as it is known, is a backless bikini top that does away with the need to readjust straps in pursuit of the perfect line-free tan.

Thanks to a gel usually used in surgery, it has amazing sticking power, staying perfectly in place.

Former teacher Jill Silver, 46, came up with the idea on holiday in Majorca, Spain, five years ago.

"I sat up and had what I call a 'clutch-moment' - which is when you hold your bikini to your chest to look modest," she said.

"I turned round to my husband and said 'I know what I really want . . . a backless, strapless bikini top'. It was a real lightbulb moment.

"I felt that sunbathing could be a real chore and that I was always working hard to eliminate the strap marks and lines from the day before.

"I wanted an even tan, with no fastening and unfastening, positioning and re-positioning of ties and straps."

The gel, which holds the top in place under the arms, is already on the fabric and lasts for about 15 wears.

The first batch of Demikinis will come with an extra supply of gel.

"The gel feels very comfortable and cooling and lets the wearer jump and bounce around as much as they want," Mrs Silver said.

The mother of two, who lives near Altrincham, Manchester, road-tested the top on summer holiday.

"I saw a lot of slightly puzzled looks that turned into stupefied gazes as I passed by," she said.

The Demikini goes on sale in Britain this week for around £26 ($65). Matching briefs cost pound £10 ($25).

Because the gel loses its sticking power in water, the top is for dry land.

Only those who really wouldn't mind going topless should dare take a dip.