A precancerous lesion can present as an isolated lesion or a certain state of the tissue. A precancerous lesion is defined as a certain tissue that is morphologically altered and has a greater likelihood of developing into a malignant lesion compared to normal mucosa. A precancerous state, on the other hand, is a certain state of tissue or a generalized disease that is not necessarily altered in appearance, but has a higher risk of developing into a malignant lesion. Precancerous lesions can be broadly classified as mucosal leukoplakia and mucosal erythroplakia. Oral leukoplakia is defined as a white plaque that occurs on the oral mucosa and cannot be diagnosed clinically or pathologically as any other disease. This plaque cannot be scraped or rubbed off, which is the main point that distinguishes it from other diseases in terms of diagnosis. White patches are a strictly clinical diagnosis and do not represent any particular pathological diagnosis. White spots usually have no subjective symptoms and have a variety of appearances, such as white or off-white in color, they may not protrude from the mucosa or may be slightly elevated, and the surface may be wrinkled or smooth. White spots can be isolated lesions or multicentric lesions and can change in shape as they progress over time. More than 70% of patients with two or more white spots in the oral cavity are male. Proliferative verrucous leukoplakia is more aggressive clinically. The lower lip redness, buccal mucosa and gums are the best sites for leukoplakia, while the majority of leukoplakia on the tongue or floor of the mouth present as abnormal growths or cancer. The relative risk of developing leukoplakia at different sites is related to regional habits and can vary according to geographical differences. Histologically, hyperkeratosis of the epithelium is a common feature of all leukoplakia, while subepithelial tissue progresses from normal to infiltrating carcinoma. The etiology of leukoplakia formation is still unclear, but there are several related factors, tobacco stimulation is one of them, whether smoking or non-smoking exposure to tobacco is closely related to leukoplakia formation. more than 70% of leukoplakia patients are smokers. Even some studies have shown that after quitting smoking, lesions can subside or shrink, while other methods do not work. Erythema specifically refers to bright red, velvety plaques on the oral mucosa, which cannot be diagnosed clinically and pathologically as other diseases, whose etiology is unknown, and which are mostly histologically abnormal epithelial hyperplasia, carcinoma in situ or early infiltrating carcinoma. Its redness is due to the lack of keratin layer on the surface of the lesion, the atrophy and thinning of the epithelial layer, and the deep connective tissue papillae containing vascular dilatation closer to the surface. The most common sites of erythema are the floor of the mouth and the posterior triangle of the molars. The etiology of erythema is not clear, but it is generally believed to be the same as the factors associated with the occurrence of leukoplakia. Erythema lesions tend to be non-homogeneous and are often adjacent to or present in white spots; lesions with this morphology are called erythematous white spots. The rate of erythema maligna is significantly higher than that of leukoplakia, approaching 23%. Oral submucosal fibrosis (OSF) is a precancerous state that often occurs in people between the ages of twenty and forty years, with the disease often occurring in the posterior cushion area and the buccal mucosa. It has a long and progressive course and is characterized by sclerosis of the mucosa, so that spasms or painful swallowing often occur when eating spicy foods, leading to speech or swallowing difficulties. It is mainly seen in Indian or Southeast Asian populations, and there are more patients in Taiwan, Hainan and Xiangtan area of Hunan Province in China. It is closely related to betel nut chewing habits, and studies have shown that OSF may be related to genetics, immunity and vitamin deficiency. Oral submucosal fibrosis does not subside or stagnate. Data from a longitudinal study showed a malignancy rate of 7.6% at 17 years of follow-up.