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What is Smokers melanosis and explain in detail?
Smokers melanosis is seen with the naked eye as a brown to black pigmentation of the oral tissue i.e. the gums, cheeks or palate  as well as in larynx. It is most often seen in the lower labial gingiva of tobacco users. Most easily it is found in Caucasians, due to their lack of a genetically caused melanin pigmentation.The brown to black colour is melanin. In skin, melanin prevents harmful UV-light from reaching deeper, sensible parts of the tissue. If UV-light penetrates deep, some of the toxic substances due to the UV-light damage to the cells, are bound to melanin in the epithelial cells and travel with the ageing cells to the skin surface, where they are expelled from the tissue surface. In this way the melanocytes and keratinocytes together protect the tissue, with melanin serving as a toxic defence and cleaning agent.
In the oral mucosa, where the ageing epithelial cells move faster to the surface compared to skin, a similar defence-mechanism seems to be present, cleaning the mucosa from different toxic chemicals penetrating the epithelium. Besides chemicals in tobacco  also antimalaria-drugs cause an oral pigmentation. Smokers melanosis is like the genetic melanin pigmentations, a defence-system in action.
The microscope shows smokers melanosis to be characterized by a melanin hyperpigmentation of the lower part of the oral epithelium, similar to sun-tanned skin. The hyperpigmentation consists of melanin granules which have the shape and colour of "coffea beans". They are produced by the dendritic, octopus-like melanocytes, seen between the epithelial cells situated closest to the epithelium/connective tissue border.In tobacco-users the melanocytes are stimulated to produce melanin granules and to distribute them out to the surrounding epithelial cells for further transport to the mucosal surface, like the mechanism in melanin-pigmented skin.
Small amounts of melanin-like granules together with other electron-dense particles can also be seen within large melanosome complexes in the underlying connective tissue. If the granules derive from the epithelium,  a phenomenon known as melanin incontinence, is not known. In Caucasians these granules are not expected to influence on the clinically observed degree of smokers melanosis.

Causes
Smoking or the use of nicotine-containing drugs is the cause to Smokers melanosis,. Also tar-components (benzopyrenes) are known to stimulate melanocytes to melanin production, and other unknown toxic agents in tobacco may also be the cause.  These chemical agents have a polycyclic, chain-like structure.  Environmental tobacco smoke from parents is causing smokers melanosis in their children    Swedish snuff causes a small elevation of oral melanin pigmented individuals from 3.0% to 4.7%. Nicotine tablets have shown to stimulate to melanin pigmentation of the oral mucosa.

Treatment and prognosis
Lesions usually disappear between 3 months to 3 years for those who stop smoking.  Smokers melanosis is a benign, normal physiological reaction, and does not develop into cancer