While the degree of dysplasia has been shown to be an important predictor of malignant change, many have challenged its use due to the low predictive value from the lack of objectivity of grading dysplasia. While 10% of leukoplakia lesions show dysplasia when biopsied, as many as 18% of oral lesions undergo malignant change in the absence of dysplasia. Leukoplakia located on the floor of the mouth, the posterior and lateral tongue, and the retromolar areas (the region behind the wisdom teeth) have higher risk, whereas white patches in areas such as the top surface of the tongue and the hard palate do not have significant risk. Although these "high risk" sites are recognized, statistically, leukoplakia is more common on the buccal mucosa, alveolar mucosa, and the lower labial mucosa. Leukoplakia of the floor of the mouth and tongue accounts for over 90% of leukoplakias showing dysplasia or carcinoma on biopsy. This is thought to be due to pooling of saliva in the lower part of the mouth, exposing these areas to more carcinogens held in suspension. Red lesions (erythroplasia) and mixed red and white lesions (erythroleukoplakia/"speckled leukoplakia") have a higher risk of malignant change than homogeneous leukoplakia. Verrucous or nodular areas have a higher risk. Although smoking increases risk of malignant transformation, smoking also causes many white patches with no dysplasia. This means that statistically, white patches in non-smokers have a higher risk. Older people with white patches are at higher risk. Larger white patches are more likely to undergo malignant transformation than smaller lesions.
Oral leukoplakia is a potentially malignant disorder affecting the oral mucosa. It is defined as "essentially an oral mucosal white lesion that cannot be considered as any other definable lesion." Oral leukoplakia is a white patch or plaque that develops in the oral cavity and is strongly associated with smoking. Leukoplakia is a firmly attached white patch on a mucous membrane which is associated with increased risk of cancer. The edges of the lesion are typically abrupt and the lesion changes with time. Advanced forms may develop red patches. There are generally no other symptoms. It usually occurs within the mouth, although sometimes mucosa in other parts of the gastrointestinal tract, urinary tract, or genitals may be affected.The cause of leukoplakia is unknown. Risk factors for formation inside the mouth include smoking, chewing tobacco, excessive alcohol, and use of betel nuts. One specific type is common in HIV/AIDS. It is a precancerous lesion, a tissue alteration in which cancer is more likely to develop. The chance of cancer formation depends on the type, with between 3–15% of localized leukoplakia and 70–100% of proliferative leukoplakia developing into squamous cell carcinoma.Leukoplakia is a descriptive term that should only be applied after other possible causes are ruled out. Tissue biopsy generally shows increased keratin build up with or without abnormal cells, but is not diagnostic. Other conditions that can appear similar include yeast infections, lichen planus, and keratosis due to repeated minor trauma.