Betel (Piper betle) is a tropical shade-loving perennial evergreen vine. It is best known as a component of "betel nut" or "betel quid". Betel quid consists of slices of "areca nut" (the seed of the palm Areca catechu) wrapped in betel leaf, often with other components such as slaked lime (calcium hydroxide paste) and tobacco or spices for flavoring.

Chewing betel quid is addictive and is reportedly done daily by as many as 600 million people globally across the Indian subcontinent and through China, Southeast Asia, and the Pacific--and immigrants to other parts of the world often continue to chew betel quid in their adopted countries. Among different populations, users may be demographically quite different, e.g., largely men in Cambodia, but mainly men among aboriginal Taiwanese. At least in the Western Pacific Region, there is evidence that the frequency of betel quid use is increasing and that this use is increasingly associated with the chewing of tobacco.

Although chewing betel quid is encouraged by some traditional medicine practitioners, there is much scientific evidence of diverse and substantial harm to the user's health resulting from this practice, such as the induction of oral precancerous lesions that have a high propensity to progress. As these negative health impacts have become clearer, this has elevated concern among public health experts, including those at the World Health Organization and the U.S. Centers for Disease Control.

(Gupta and Ray 2004; Lin et al. 2006 and references therein; Blank et al. 2008; Singh et al. 2012 and references therein; Al-Rmalli et al. 2011 and references therein)