In centres of orthodoxy such as Golders Green and Stamford Hill in London or Prestwich in Manchester, a lively trade goes on almost unnoticed. In small salons, usually at the back of people's homes, sheitels are sold to legions of orthodox women. The wig trade is a peculiar synthesis of high fashion and religious fundamentalism, but it is rarely mentioned because strictly orthodox Jews are reticent about their lifestyle.
Sarah Lew, the wife of one of Hackney's orthodox councillors, runs a salon from the basement of her Stamford Hill house - in between caring for eight children aged from 2 to 17. Her salon is one of the largest sheitel suppliers in the orthodox community, running daily deliveries all over London and beyond. The salon comprises two rooms, into which are packed - apart from the wigs - hundreds of bottles of lotions and gel and polystyrene heads, imported en masse from the United States.
According to religious law, a woman's natural hair provokes lustfulness, and must be concealed after marriage. For most strictly orthodox Jews, this entails wearing a wig.
Sheitels range in price enormously. Martin Bond in Stanmore makes top-of-the- range wigs for around pounds 800 each. The price varies according to the length and colour - blond hair is the most expensive. The hair comes from developing countries because European hair is too often weakened by perming or bleaching.
The wigs are made to measure, and the hair is sewn into specially constructed caps. They are then finished by hairdressers. 'My stylists have to cut the wig while it is on the woman's head, to make it look really good,' says Mr Bond.
Most orthodox women will wear cheaper wigs than this. The small salons import wigs from the United States, which has a large range of companies catering to the Jewish sheitel trade. Sarah Lew sells a range known as 'Georgie', which has around 70 different styles, from pounds 60 to pounds 175, with anything from 100 per cent natural hair to 100 per cent synthetic.
Mrs Lew says the wigs are not awkward to wear. 'They don't get hot in summer. They only weigh around two ounces. Perhaps somebody who wears a bikini in the street might think that's heavy. You get used to it]'
Contrary to common belief, the wigs are not intended to be ugly. 'You might put on clothes to cover your body, but you still want them to be attractive. In the same way, you want a wig that will look nice.'
Until the last century, orthodox women covered their heads with scarves or hats because wigs were too expensive. Different orthodox groups have different customs. The Hatan Sofer, a great rabbi of the 19th century, denounced sheitels made of real hair. His followers, in keeping with his pronouncements, still wear synthetic wigs. The Belzer Rebbe, leader of a major Hasidic grouping, complained that sheitels were becoming so realistic that it was impossible to say who was married and who was not. His married followers wear hats on top of their sheitels to avoid confusion.
Members of Satmar, the largest and richest Hasidic group, wear scarves over their sheitels in synagogue. Other leaders have stipulated that followers should not have sheitels longer than shoulder length.
Under the sheitel, real hair can be any length. 'Orthodox women don't always shave off the hair under their wig. Some have long ponytails, others will have short wedge cuts. It varies,' says Mrs Lew.
Although sheitels have their roots in tradition, they do move with the times. A recent arrival is a special Hillary Clinton wig. However women are more likely to get their wigs reshaped and trimmed than buy a new one. Mrs Lew supplies a video - recited in a soft American accent with light orchestral backing music - explaining how to restyle the wigs, which have names like 'Princess Sophia' and 'Spoilt'.
Most orthodox women go for fairly traditional cuts. A lot of them like fringes, because then a slight slip of the wig won't be noticed. 'You have to supply what people want,' says Mrs Lew. 'Some people like a wedge, others look cute in a curly wig. We may have to cut it, to give shape, or we may have to put curlers in to give it a really good finish.'
Wigs make good gifts. A newly-wed bride may receive two or three from close family and pick up more when attending weddings or barmitzvahs. 'We sell a lot of wigs around the high holidays,' says Mrs Lew. 'When children visit from abroad on the holidays, they'll often buy their mother a wig before they go home.'
As the strictly orthodox community grows in size, sometimes attracting newcomers from the mainstream, so sheitels are penetrating other parts of the Jewish community. 'When less orthodox women visit their more orthodox grandchildren, they'll often wear a sheitel so as to respect the modesty of that home,' says Mrs Lew.
Not all sheitel-wearers are hung up about fashion. Older women are less likely to be fashion-conscious. 'I don't worry too much,' says Mrs Freda Vorst, a veteran sheitel-wearer. 'I use a mix of nylon and real hair because it's easier to look after. I wash it every couple of weeks. I wouldn't like to be mutton dressed as lamb.'