We are born without any, or with very little. We grow up resisting attempts to wash it, tame it or cut it, but by the time we are adults most of us have developed a certain attachment to our hair. It’s personal. Other people’s hair is another matter. We lovingly stroke the hair of dogs and cats, wear clothing made from the hair of sheep or rabbits, but the sight of a stranger’s hair on our clothes, in the shower or – heaven forbid – in our food provokes disgust.

Hair gives rise to complex emotions. A healthy head of hair can symbolise power, youth and virility; forcibly cutting or shaving someone’s hair can be seen as an act of violation. Hair is the stuff of folklore, fantasy and fetish. In the fairytale, Rapunzel lets down her hair to escape imprisonment; in the biblical story, Delilah cuts Samson’s hair to deprive him of his strength.

There’s no doubt that hair is entwined within our culture, traditions and history. Yet few could begin to guess at the hidden life of hair in the world today. Anthropologist Emma Tarlo has spent three years following the trail of human hair as it winds around the globe as part of a billion-dollar industry that produces not only wigs and hair extensions but also fertilisers, cosmetics, pet foods and even artworks. In Entanglement, she unravels a story that is by turns surprising, unsettling and disturbing but never anything less than absorbing.

The market for human hair goes back a long way. In the 19th century, peasants across Europe sold their own and their children’s hair at markets to eke out slender incomes. At auctions in France, girls were displayed on platforms and their long hair was sold to the highest bidder before being shorn on the spot. In Britain, pedlars visited country fairs to persuade young girls to part with their locks in exchange for trinkets. The harvested hair was then fashioned into wigs and hairpieces to be sold to wealthy customers in shops in Paris, London and New York. Today hair is still predominantly sourced from the poor to provide embellishments for the rich, yet the centre of trade has switched from West to East.

Much of the most highly prized hair today comes from Hindu temples in south India, where men, women and children converge to have their heads shaved as an act of devotion. This ‘temple hair’ is sorted by hand, then sold to raise funds for social and welfare projects; one temple clearing house raises £20 million a year from hair sales.

Most hair from India, along with hair collected in Myanmar and Bangladesh, is sent to huge factories in China, where it is bleached or dyed a spectrum of hues from blonde to brown, is curled, crinkled or relaxed and is then crafted into a dizzying range of wigs or packaged for hair extensions. China is the world’s biggest exporter of wigs and extensions made from both human and synthetic hair. One city, Xuchang, has so many factories devoted to hair processing that it is known as Hair City.

Most wigs and hair goods are exported to America, Europe and Africa. A curly blonde wig on sale in London or New York may well have started life as straight black hair clipped in India. But demand for wigs and hairpieces is so great that supplies are supplemented by waste hair salvaged from combings in south and southeast Asia. Balls of discarded hair are collected by pedlars going from door to door by bicycle or boat in Myanmar, Bangladesh and India and then laboriously disentangled, sorted into lengths and packaged by villagers paid about £1 a day. A single wig may, therefore, contain hair collected from hundreds of heads.

Unpicking all this, Tarlo travels the globe to meet the pilgrims, barbers, peasants, factory workers and entrepreneurs involved in the making of wigs and hairpieces, as well as the traders and customers who make the commodity such big business. In this lucrative and unregulated market, exploitation, corruption and crime are rife. Hair sold as ‘Russian blonde’ may well be bleached Indian hair packaged in China, while products labelled ‘100% human hair’ often contain animal or synthetic fibres. And despite the interlocking trade connections, cultural differences can sometimes come to the fore. When the US banned the import of ‘communist hair’ from China in 1966, production switched wholesale to Hong Kong; in 2004 many New York wig suppliers went bust when a prominent Jerusalem rabbi declared a ban on Indian ‘temple hair’.

Although it may seem an unsavoury, even seedy industry, Tarlo makes no moral judgements. Approaching the subject with cultural sensitivity and scientific curiosity, she talks to Orthodox Jewish women in Golders Green salons who pay large sums to cover their own hair with wigs (sheitels) made from other people’s hair, as well as to women who have lost hair as a result of cancer or alopecia. Visiting hair fairs in America and salons in Senegal, she explores the debate among black women who spend fortunes straightening, braiding and supplementing their own hair in the face of opponents who champion the ‘natural hair’ movement.

Rather than taking a strict chronological or geographical route, the book meanders from one country to another, weaving in history, politics and science in an interlocking, mesmerising narrative that seems wholly appropriate to the subject.