Most cases of leukoplakia cause no symptoms, but infrequently there may be discomfort or pain. The exact appearance of the lesion is variable. Leukoplakia may be white, whitish yellow or grey. The size can range from a small area to much larger lesions. The most common sites affected are the buccal mucosa, the labial mucosa and the alveolar mucosa, although any mucosal surface in the mouth may be involved. The clinical appearance, including the surface texture and color, may be homogenous or non-homogenous (see: classification). Some signs are generally associated with a higher risk of cancerous changes (see: prognosis).

Leukoplakia may rarely be associated with esophageal carcinoma.

In the context of lesions of the mucous membrane lining of the bladder, leukoplakia is a historic term used to describe a visualized white patch which histologically represents keratinization in an area of squamous metaplasia. The symptoms may include frequency, suprapubic pain (pain felt above the pubis), hematuria (blood in the urine), dysuria (difficult urination or pain during urination), urgency, and urge incontinence. The white lesion may be seen during cystoscopy, where it appears as a whitish-gray or yellow lesion, on a background of inflamed urothelium and there may be floating debris in the bladder. Leukoplakia of the bladder may undergo cancerous changes, so biopsy and long term follow up are usually indicated.

There is a diffuse, gray-white, milky opalescent appearance of the mucosa which usually occurs bilaterally on the buccal mucosa. Less often, the labial mucosa, the palate or the floor of mouth may be affected. The surface of the area is folded, creating a wrinkled, white streaked lesion. Apart from the appearance, the lesion is entirely asymptomatic.

On the shaft of the penis, Fordyce spots are more visible when the skin is stretched, and may only be noticeable during an erection.

The spots can also appear on the skin of the scrotum.

Oral Fordyce granules appear as rice-like granules, white or yellow-white in color. They are painless papules (small bumps), about 1–3 mm in greatest dimension. The most common site is along the line between the vermilion border and the oral mucosa of the upper lip, or on the buccal mucosa (inside the cheeks) in the commissural region, often bilaterally. They may also occur on the mandibular retromolar pad and tonsillar areas, but any oral surface may be involved. There is no surrounding mucosal change. Some patients will have hundreds of granules while most have only one or two.

Occasionally, several adjacent glands will coalesce into a larger cauliflower-like cluster similar to sebaceous hyperplasia of the skin. In such an instance, it may be difficult to determine whether or not to diagnose the lesion as sebaceous hyperplasia or sebaceous adenoma. The distinction may be moot because both entities have the same treatment, although the adenoma has a greater growth potential. Sebaceous carcinoma of the oral cavity has been reported, presumably arising from Fordyce granules or hyperplastic foci of sebaceous glands.

In some persons with Fordyce spots, the glands express a thick, chalky discharge when squeezed.

Although often the terms "erythroplasia" and "erythroplakia" are used synonymously, some sources distinguish them, stating that the latter is maccular (flat) while the former is papular (bumpy).

Erythroplakia of the genital mucosae is often referred to as erythroplasia of Queyrat.

The most common areas in the mouth where erythroplakia is found are the floor of the mouth, buccal vestibule, the tongue, and the soft palate. It appears as a red macule or plaque with well-demarcated borders. The texture is characterized as soft and velvety. An adjacent area of leukoplakia may be found along with the erythroplakia.

Erythroplasia may also occur on the laryngeal mucosa, or the anal mucosa.

Oral lichen planus (also termed "oral mucosal lichen planus"), is a form of mucosal lichen planus, where lichen planus involves the oral mucosa, the lining of the mouth. This may occur in combination with other variants of lichen planus. Six clinical forms of oral lichen planus are recognized:

- "Reticular", the most common presentation of oral lichen planus, is characterised by the net-like or spider web-like appearance of lacy white lines, oral variants of Wickham's straiae. This is usually asymptomatic.

- "Erosive/ulcerative", the second most common form of oral lichen planus, is characterised by oral ulcers presenting with persistent, irregular areas of redness, ulcerations and erosions covered with a yellow slough. This can occur in one or more areas of the mouth. In 25% of people with erosive oral lichen planus, the gums are involved, described as desquamative gingivitis (a condition not unique to lichen planus). This may be the initial or only sign of the condition.

- "Papular," with white papules.

- "Plaque-like" appearing as a white patch which may resemble leukoplakia.

- "Atrophic," appearing as areas. Atrophic oral lichen planus may also manifest as desquamative gingivitis.

- "Bullous," appearing as fluid-filled vesicles which project from the surface.

These types often coexist in the same individual. Oral lichen planus tends to present bilaterally as mostly white lesions on the inner cheek, although any mucosal site in the mouth may be involved. Other sites, in decreasing order of frequency, may include the tongue, lips, gingivae, floor of the mouth, and very rarely, the palate.

Generally, oral lichen planus tends not to cause any discomfort or pain, although some people may experience soreness when eating or drinking acidic or spicy foodstuffs or beverages. When symptoms arise, they are most commonly associated with the atrophic and ulcerative subtypes. These symptoms can include a burning sensation to severe pain. Lichen planus, particularly when concomitant oral or genital lesions occur, significantly affects patients’ quality of life.

Sebaceous glands are normal structures of the skin but may also be found ectopically in the mouth, where they are referred to as "oral Fordyce granules" or ectopic sebaceous glands.

On the foreskin they are called Tyson's glands, not to be confused with hirsuties coronae glandis.

When they appear on the penis, they are also called "penile sebaceous glands".

When seen as a streak of individual glands along the interface between the skin of the lip and the vermilion border, the terms Fox–Fordyce disease and Fordyce's condition have been used.

It presents itself in the mouth, most frequently as a thick, bilateral, symmetrical white plaques with a spongy, corrugated or velvety texture. Most usually, the lesions are on the buccal mucosa, but sometimes on the labial mucosa, alveolar ridge, floor of the mouth, ventral surface of the tongue or soft palate. The gingival margin and dorsum of the tongue are almost never affected. Less commonly, sites outside the mouth are affected, including the nasal, esophageal, laryngeal, anal and genital mucosae. It usually is present from birth, or develops during childhood. Rarely, the lesions may develop during adolescence. Apart from the appearance of the affected areas, there are usually no other signs or symptoms.

Lichen planus affecting mucosal surfaces may have one lesion or be multifocal. Examples of lichen planus affecting mucosal surfaces include:

- "Esophageal lichen planus", affecting the esophageal mucosa. This can present with difficulty or pain when swallowing due to oesophageal inflammation, or as the development of an esophageal stricture. It has also been hypothesized that it is a precursor to squamous cell carcinoma of the esophagus.

- "Genital lichen planus," which may cause lesions on the glans penis or skin of the scrotum in males, and the vulva or vagina in females. Symptoms may include lower urinary tract symptoms associated with stenosis of the urethra, painful sexual intercourse, and itching. In females, "Vulvovaginal-gingival syndrome," is severe and distinct variant affecting the vulva, vagina, and gums, with complications including scarring, vaginal stricture formation, or vulva destruction. The corresponding syndrome in males, affecting the glans penis and gums, is the "peno-gingival syndrome". It is associated with HLA-DQB1.

Leukoedema lesions disappear when the mucosa is stretched, which helps to differentiate it from other white lesions in the mouth. The differential diagnosis is with leukoplakia, oral candidiasis, oral lichen planus, white sponge nevus, morsicatio buccarum, hereditary benign intraepithelial dyskeratosis and dyskeratosis congenita. Tissue biopsy is not indicated, but when taken, the histologic appearance is one of increased epithelial thickness, broadening and eleongation of the rete ridges, parakeratosis and intracellular edema of the spinous layer. The cells of the spinous later are vacuolated, large and possess pyknotic nuclei. The superficial squamous cells have a clear, seemingly empty cytoplasm but it has not been shown that there is an increase in intracellular water, possibly making the term edema misleading. The histologic appearance is thought to be caused by water within the cells of the spinous layer causing the light to reflect back as whitish. The diagnosis is usually made based on the clinical appearance alone, but oral exfoliative cytology has been used as a diagnostic aid.

The palate may appear gray or white and contain many papules or nodules that are slightly elevated with red dots in their center. These red dots represent the ducts of minor salivary glands which have become inflamed by heat. The condition is painless. If a denture is normally worn while smoking, then the mucosa underneath the denture appears unaffected by the condition. In severe cases, the mucosa may show fissuring and develop a "dried lake bed" appearance. Other changes associated with tobacco use may be evident such as brown or black extrinsic staining of teeth from tar and other components of tobacco smoke.

In the initial phase of the disease, the mucosa feels leathery with palpable fibrotic bands. In the advanced stage the oral mucosa loses its resiliency and becomes blanched and stiff. The disease is believed to begin in the posterior part of the oral cavity and gradually spread outward.

Other features of the disease include:

- Xerostomia

- Recurrent ulceration

- Pain in the ear or deafness

- Nasal intonation of voice

- Restriction of the movement of the soft palate

- A budlike shrunken uvula

- Thinning and stiffening of the lips

- Pigmentation of the oral mucosa

- Dryness of the mouth and burning sensation

- Decreased mouth opening and tongue protrusion

The lesions are located on the mucosa, usually bilaterally in the central part of the anterior buccal mucosa and along the level of the occlusal plane (the level at which the upper and lower teeth meet). Sometimes the tongue or the labial mucosa (the inside lining of the lips) is affected by a similarly produced lesion, termed morsicatio linguarum and morsicatio labiorum respectively. There may be a coexistent linea alba, which corresponds to the occlusal plane, or crenated tongue. The lesions are white with thickening and shredding of mucosa commonly combined with intervening zones of erythema (redness) or ulceration. The surface is irregular, and people may occasionally have loose sections of mucosa that comes away.

Also called smoker's palatal keratosis, this condition may occur in smokers, especially pipe smokers. The palate appears dry and cracked, and white from keratosis. The minor salivary glands appear as small, red and swollen bumps. It is not a premalignant condition, and the appearance reverses if the smoking is stopped.

The term "necrotizing ulcerative gingivostomatitis" is sometimes used as a synonym of the necrotizing periodontal disease more commonly termed necrotizing ulcerative gingivitis, or a more severe form (also termed necrotizing stomatitis). The term "necrotizing gingivostomatitis" is also sometimes used.

The word erythroplakia means "red patch", and is derived from the Greek words ερυθρος - "red" and πλάξ - "plate"

The World Health Organization defines oral erythroplakia as follows:

The cause is chronic parafunctional activity of the masticatory system, which produces frictional, crushing and incisive damage to the mucosal surface and over time the characteristic lesions develop. Most people are aware of a cheek chewing habit, although it may be performed subconsciously. Sometimes poorly constructed prosthetic teeth may be the cause if the original bite is altered. Usually the teeth are placed too far facially (i.e. buccally and/or labially), outside the "neutral zone", which is the term for the area where the dental arch is usually situated, where lateral forces between the tongue and cheek musculature are in balance. Glassblowing involves chronic suction and may produce similar irritation of the buccal mucosa. Identical, or more severe damage may be caused by self-mutilation in people with psychiatric disorders, learning disabilities or rare syndromes (e.g. Lesch-Nyhan syndrome and familial dysautonomia).

Stomatitis nicotina (also known as nicotine stomatitis, nicotinic stomatitis, nicotine palatinus, stomatitis palatini, leukokeratosis nicotina palate, palatal leukokeratosis, smoker's keratosis, smoker's palate, and smoker's patches), is a diffuse white patch on the hard palate, usually caused by tobacco smoking, usually pipe or cigar smoking. It is painless, and it is caused by a response of the palatal oral mucosa to chronic heat. A more pronounced appearance can occur with reverse smoking, sometimes distinguished from stomatitis nicotina by the term reverse smoker's keratosis. While stomatitis nicotina that is caused by heat is not a premaligant condition (i.e. it does not carry an increased risk of transformation to oral cancer), the condition that is caused by reverse smoking is premalignant.

White sponge nevus (WSN, or white sponge naevus, Cannon's disease, hereditary leukokeratosis of mucosa, white sponge nevus of Cannon, familial white folded dysplasia, or oral epithelial nevus), is an autosomal dominant condition of the oral mucosa (the mucous membrane lining of the mouth). It is caused by a mutations in certain genes coding for keratin, which causes a defect in the normal process of keratinization of the mucosa. This results in lesions which are thick, white and velvety on the inside of the cheeks within the mouth. Usually, these lesions are present from birth or develop during childhood. The condition is entirely harmless, and no treatment is required.

The appearance of pyogenic granuloma is usually a color ranging from red/pink to purple, and can be smooth or lobulated. Younger lesions are more likely to be red because of the high number of blood vessels. Older lesions begin to change into a pink color. Size commonly ranges from a few millimeters to centimeters, though smaller or larger lesions may occur. A pyogenic granuloma can be painful, especially if located in an area of the body where it is constantly disturbed. Pyogenic granulomas can grow rapidly and will often bleed profusely with little or no trauma. They may exude an oil like substance, causing the surface to be damp. This is especially true if the granuloma is located on the scalp.

Pyogenic granulomas may be seen at any age, and are more common in females than males. In pregnant women, lesions may occur in the first trimester with an increasing incidence up until the seventh month, and are often seen on the gums. Epulis granulomatosum is a variant of pyogenic granuloma that forms only on gingiva, and is often seen forming in a recent extraction socket. Pyogenic granulomas appear on the gingiva in 75% of cases, more often in the maxillary than mandibular jaw. Anterior areas are more often affected than posterior areas. It can also be found on the lips, tongue, and inner cheek. Poor oral hygiene or trauma are usually precipitating factors.

One study has suggested a correlation between pyogenic granulomas and Bartonella seropositivity. However, this association has been questioned by others. The microscopic appearance of a pyogenic granuloma consists of highly vascular granulation tissue. Inflammation is present. The lesion may have a fibrous character if it is older, and the surface may have ulcerations. Pyogenic granulomas rarely occur in the conjunctiva, cornea or connective tissue of the eye following minor local trauma. Grossly these mass lesions resemble those occurring at more common sites. The relationship of these lesion to lobular capillary hemangiomas of skin and oropharyngeal mucosa commonly referred to as pyogenic granuloma is uncertain.

Aphthous stomatitis is a common condition characterized by the repeated formation of benign and non-contagious mouth ulcers (aphthae) in otherwise healthy individuals. The informal term canker sores is also used, mainly in North America, although this may also refer to any mouth ulcer.

The cause is not completely understood, but involves a T cell-mediated immune response triggered by a variety of factors. Different individuals have different triggers, which may include nutritional deficiencies, local trauma, stress, hormonal influences, allergies, or genetic predisposition.

These ulcers occur periodically and heal completely between attacks. In the majority of cases, the individual ulcers last about 7–10 days, and ulceration episodes occur 3–6 times per year. Most appear on the non-keratinizing epithelial surfaces in the mouth (i.e. anywhere except the attached gingiva, the hard palate and the dorsum of the tongue), although the more severe forms, which are less common, may also involve keratinizing epithelial surfaces. Symptoms range from a minor nuisance to interfering with eating and drinking. The severe forms may be debilitating, even causing weight loss due to malnutrition.

The condition is very common, affecting about 20% of the general population to some degree. The onset is often during childhood or adolescence, and the condition usually lasts for several years before gradually disappearing. There is no cure, and treatments aim to manage pain, reduce healing time and reduce the frequency of episodes of ulceration. The term is from meaning "mouth ulcer".

Oral submucous fibrosis is clinically divided into three stages:

- Stage 1: Stomatitis

- Stage 2: Fibrosis

- a- Early lesions, blanching of the oral mucosa

- b- Older lesions, vertical and circular palpable fibrous bands in and around the mouth or lips, resulting in a mottled, marble-like appearance of the buccal mucosa

- Stage 3: Sequelae of oral submucous fibrosis

- a- Leukoplakia

- b- Speech and hearing deficits

Khanna and Andrade in 1995 developed a group classification system for the surgical management of trismus:

- Group I: Earliest stage without mouth opening limitations with an interincisal distance of greater than 35 mm.

- Group II: Patients with an interincisal distance of 26–35 mm.

- Group III: Moderately advanced cases with an interincisal distance of 15–26 mm. Fibrotic bands are visible at the soft palate, and pterygomandibular raphe and anterior pillars of fauces are present.

- Group IVA: Trismus is severe, with an interincisal distance of less than 15 mm and extensive fibrosis of all the oral mucosa.

- Group IVB: Disease is most advanced, with premalignant and malignant changes throughout the mucosa.

Due to its overwhelming incidence on the gingiva, the condition is often associated with two other diseases, though not because they occur together. Instead, the three are associated with each other because they appear frequently on gingiva—peripheral giant cell granuloma and peripheral ossifying fibroma. Detailed analysis can be used to distinguish these conditions.

The most common location by far is the gingival margin and other areas of the masticatory oral mucosa, these occur more frequently in the fifth decade of life, and have good prognosis, the treatment of choice for oral VXs is surgical excision, and recurrence is rare.

The condition can affect other organs of body, such as the penis, vulva, and can occur in anal region, nose, the ear, lower extremity, scrotum.

Localised discoid lupus erythematosus typically presents with skin lesions localised above the neck, with favoured sites being the scalp, bridge of the nose, cheeks, above the lips and ears as well as the arms hair scratching glasses touching name="Andrews1"/> Another form of discoid lupus erythematosus includes oral discoid. Oral discoid lupus erythematosus results in oral lesions which present themselves as white spots, ulcers and central erythema lesions. Oral discoid lesions most commonly occur on the labial mucosa, vermillion border and buccal mucosa. Atrophy may be observed in some cases. Dentists may be important in establishing the diagnosis before the cutaneous lesions become apparent.