Paan is a preparation combining betel leaf with areca nut and sometimes also with tobacco.It is chewed for its stimulant and psychoactive effects.After chewing it is either spat out or swallowed. Paan has many variations. Slaked lime (chunnam) paste is commonly added to bind the leaves. Some South Asian preparations include katha paste or mukhwas to freshen the breath.

The origin and diffusion of paan (betel chewing) remains a somewhat unresolved issue since there is little equivocal evidence to support the very early dates often quoted, though botanical evidence strongly suggests that the areca palm was not native to South Asia.Paan (under a variety of names) is also consumed in many other Asian countries and elsewhere in the world by some Asian emigrants, with or without tobacco. It is an addictive and euphoria-inducing formulation with adverse health effects.

The spit from chewing betelnuts, known as buai pekpek, is often considered an eyesore. Because of this, many places have banned selling and chewing buai.

Source:Wikipedia