Betel chewing products, used from time immemorial in India and elsewhere in Asia as a mild stimulent and consumed even by children, are a major cancer hazard, according to a new study released on Thursday.

Countries where betel chewing is prevalent have higher rates of cancer of the mouth, pharynx and oesophagus, and Asian immigrant communities also suffer more from these diseases than the surrounding population, according to the report by the International Agency for Research on Cancer (IARC).

"There are hundreds of millions of users worldwide, and there is great concern that the habit will spread to populations in North America and Europe not previously exposed to the habit," the agency said. Britain is the world's leading importer of betel products outside Asia, it added.

A common product known as betel quid is a kind of candy made from areca tropical palm nuts, slaked lime and spices, and wrapped in a leaf from the betel vine. Tobacco is often added to the mix.

The quid is held between the teeth and the cheek, where it slowly releases a stimulant called arecoline. People who use betel frequently over a long period of time usually have red teeth. They are also likely, the new study finds, to suffer from a hardening of tissue called oral submucous fibrosis, which can turn into cancer.