The exact underlying cause of<unk>  is largely unknown, but it is likely multifactorial, with the main factor being the use of tobacco. Tobacco use and other suggested causes are discussed below. The mechanism of the white appearance is thickening of the keratin layer, called hyperkeratosis. The abnormal keratin appears white when it becomes hydrated by saliva, and light reflects off the surface evenly. This hides the normal pink-red color of mucosae (the result of underlying vasculature showing through the epithelium). A similar situation can be seen on areas of thick skin such as the soles of the feet or the fingers after prolonged immersion in water. Another possible mechanism is thickening of the stratum spinosum, called acanthosis. Tobacco Tobacco smoking or chewing is the most common causative factor, with more than 80% of persons with<unk>  having a positive smoking history. Smokers are much more likely to suffer from<unk>  than non-smokers. The size and number of<unk>  lesions in an individual is also correlated with the level of smoking and how long the habit has lasted for. Other sources argue that there is no evidence for a direct causative link between smoking and oral<unk> . Cigarette smoking may produce a diffuse<unk>  of the buccal mucosa, lips, tongue and rarely the floor of mouth. Reverse smoking, where the lit end of the cigarette is held in the mouth is also associated with mucosal changes. Tobacco chewing, e.g. betel leaf and areca nut, called paan, tends to produce a distinctive white patch in a buccal sulcus termed "tobacco pouch keratosis". In the majority of persons, cessation triggers shrinkage or disappearance of the lesion, usually within the first year after stopping. Alcohol Although the synergistic effect of alcohol with smoking in the development of oral cancer is beyond doubt, there is no clear evidence that alcohol is involved in the development of<unk> , but it does appear to have some influence. Excessive use of a high alcohol-containing mouth wash (> 25%) may cause a grey plaque to form on the buccal mucosa, but these lesions are not considered true<unk> . Sanguinaria Sanguinaria (Bloodroot) is a herbal extract that is included in some toothpastes and mouthwashes. Its use is strongly associated with development of<unk> , usually in the buccal sulcus. This type of<unk>  has been termed "sanguinaria associated keratosis" and more than 80% of people with<unk>  in the vestibule of the mouth have used this substance. Upon stopping contact with the causative substance, the lesions may persist for years. Although this type of<unk>  may show dysplasia, the potential for malignant transformation is unknown. Ultraviolet radiation Ultraviolet radiation is believed to be a factor in the development of some<unk>  lesions of the lower lip, usually in association with actinic cheilitis. Micro-organisms Candida in its pathogenic hyphal form is occasionally seen in biopsies of idiopathic<unk> . It is debated whether candida infection is a primary cause of<unk>  with or without dysplasia, or a superimposed (secondary) infection that occurs after the development of the lesion. It is known that Candida species thrive in altered tissues. Some<unk> s with dysplasia reduce or disappear entirely following use of antifungal medication. Smoking, which as discussed above can lead to the development of<unk> , can also promote oral candidiasis. Candida in association with<unk>  should not be confused with white patches which are primarily caused by candida infection, such as chronic hyperplastic candidiasis ("candidal<unk> "). The involvement of viruses in the formation of some oral white lesions is well established, e.g. Epstein-Barr virus in oral hairy<unk>  (which is not a true<unk> . Human papilloma virus (HPV), especially HPV 16 and 18, is sometimes found in areas of<unk> , however, since this virus can be coincidentally found on normal, healthy mucosal surfaces in the mouth, it is unknown if this virus is involved in the development of some<unk> s. In vitro experimentation has demonstrated that HPV 16 is capable of inducing dysplastic changes in previously normal squamous epithelium. Epithelial atrophy<unk>  is more likely to develop in areas of epithelial atrophy. Conditions associated with mucosal atrophy include iron deficiency, some vitamin deficiencies, oral submucous fibrosis, syphilis and sideropenic dysphagia. Trauma Another very common cause of white patches in the mouth is frictional or irritational trauma leading to keratosis. Examples include nicotine stomatitis, which is keratosis in response to heat from tobacco smoking (rather than a response to the carcinogens in tobacco smoke). The risk of malignant transformation is similar to normal mucosa. Mechanical trauma, e.g. caused by a sharp edge on a denture, or a broken tooth, may cause white patches which appear very similar to<unk> . However, these white patches represent a normal hyperkeratotic reaction, similar to a callus on the skin, and will resolve when the cause is removed. Where there is a demonstrable cause such as mechanical or thermal trauma, the term idiopathic<unk>  should not be used.
Leukoplakia
Lichen planus
Malakoplakia
Oral candidiasis
Hairy leukoplakia
Keratosis
Polypill
Geographic tongue