Hairy tongue occurs in about 0.5% of adults. However, the prevalence is variable depending on the population studied.

The cause is uncertain, but it is thought to be caused by accumulation of epithelial squames and proliferation of chromogenic (i.e., color-producing) microorganisms. There may be an increase in keratin production or a decrease in normal desquamation (shedding of surface epithelial cells). Many people with BHT are heavy smokers. Other possible associated factors are poor oral hygiene, general debilitation, hyposalivation (i.e., decreased salivary flow rate), radiotherapy, overgrowth of fungal or bacterial organisms, and a soft diet. Occasionally, BHT may be caused by the use of antimicrobial medications (e.g., tetracyclines), or oxidizing mouthwashes or antacids. A soft diet may be involved as normally food has an abrasive action on the tongue, which keeps the filiform papillae short. Pellagra, a condition caused by a vitamin deficiency, may cause a thick greyish fur to develop on the dorsal tongue, along with other oral signs.

Transient surface discoloration of the tongue and other soft tissues in the mouth can occur in the absence of hairy tongue. Causes include smoking (or betel chewing), some foods and beverages (e.g., coffee, tea or liquorice), and certain medications (e.g., chlorhexidine, iron salts, or bismuth subsalicylate (Pepto-Bismol)).

The cause is unknown. Geographic tongue does not usually cause any symptoms, and in those cases where there are symptoms, an oral parafunctional habit may be a contributory factor. Persons with parafunctional habits related to the tongue may show scalloping on the sides of the tongue (crenated tongue). Some suggest that hormonal factors may be involved, because one reported case in a female appeared to vary in severity in correlation with oral contraceptive use. People with geographic tongue frequently claim that their condition worsens during periods of psychologic stress. Geographic tongue is inversely associated with smoking and tobacco use. Sometimes geographic tongue is said to run in families, and it is reported to be associated with several different genes, though studies show family association may also be caused by similar diets. Some have reported links with various human leukocyte antigens, such as increased incidence of HLA-DR5, HLA-DRW6 and HLA-Cw6 and decreased incidence in HLA-B51. Vitamin B2 deficiency (ariboflavinosis) can cause several signs in the mouth, possibly including geographic tongue, although other sources state that geographic tongue is not related to nutritional deficiency. Fissured tongue often occurs simultaneously with geographic tongue, and some consider fissured tongue to be an end stage of geographic tongue.

In the past, some research suggested that geographic tongue was associated with diabetes, seborrheic dermatitis and atopy, however newer research does not corroborate these findings. Others suggest allergy as a major factor, e.g. to nickel sulphate. Some studies have reported a link between geographic tongue and psoriasis, although 90% of children who are diagnosed with geographic tongue do not develop psoriasis. Again however, modern research studies do not support any link between psoriasis and geographic tongue. Lesions that are histologically indistinguishable from geographic tongue may also be diagnosed in reactive arthritis (arthritis, uveitis/conjunctivitis and urethritis).

This phenomenon is fairly common, with one in every 800 adults showing evidence of active lesions at any one time. It is more common in people who are experiencing stress or psychological conditions. The prevalence in females is double the prevalence in males, and it is two or three times more prevalent in people over the age of thirty-five.

Good oral hygiene (thorough tooth brushing and flossing and regular professional cleaning and examination) may be helpful to prevent these disorders. Drinking plenty of water and the production of enough saliva, aid in the reduction of bacterial growth. Minimizing irritants or injury in the mouth when possible can aid in the prevention of glossitis. Avoiding excessive use of any food or substance that irritates the mouth or tongue may also help.

Tongue lesions are very common. For example, in the United States one estimated point prevalence was 15.5% in adults. Tongue lesions are more common in persons who wear dentures and tobacco users. The most common tongue conditions are geographic tongue, followed by fissured tongue and hairy tongue.

One review reported overall prevalence ranges of 0.1–14.3% for geographic tongue, 1.3–9.0% for "atrophy tongue" (atrophic glossitis), and 0.0–3.35% for median rhomboid glossitis.

In traditional Chinese medicine, scalloping of the tongue is said to indicate qi vacuity. In some homeopathic sources, scalloping of the tongue is said to be indicative of high blood pressure.

There are many oral and maxillofacial pathologies which are not fully understood.

- Burning mouth syndrome (BMS) is a disorder where there is a burning sensation in the mouth that has no identifiable medical or dental cause. The disorder can affect anyone but tends to occur most often in middle aged women. BMS has been hypothesized to be linked to a variety of factors such as the menopause, dry mouth (xerostomia) and allergies. BMS usually lasts for several years before disappearing for unknown reasons. Other features of this disorder include anxiety, depression and social isolation. There is no cure for this disorder and treatment includes use of hydrating agents, pain medications, vitamin supplements or the usage of antidepressants.

- Aphthous stomatitis is a condition where ulcers (canker sores) appear on the inside of the mouth, lips and on tongue. Most small canker sores disappear within 10–14 days. Canker sores are most common in young and middle aged individuals. Sometimes individuals with allergies are more prone to these sores. Besides an awkward sensation, these sores can also cause pain or tingling or a burning sensation. Unlike herpes sores, canker sores are always found inside the mouth and are usually less painful. Good oral hygiene does help but sometime one may have to use a topical corticosteroid.

- Migratory stomatitis is a condition that involves the tongue and other oral mucosa. The common migratory glossitis (geographic tongue) affects the anterior two thirds of the dorsal and lateral tongue mucosa of 1% to 2.5% of the population, with one report of up to 12.7% of the population. The tongue is often fissured, especially. in elderly individuals. In the American population, a lower prevalence was reported among Mexican Americans (compared with Caucasians and African Americans) and cigarette smokers. When other oral mucosa, beside the dorsal and lateral tongue, are involved, the term migratory stomatitis (or ectopic geographic tongue) is preferred. In this condition, lesions infrequently involve also the ventral tongue and buccal or labial mucosa. They are rarely reported on the soft palate and floor of the mouth.

Geographic tongue is a common condition, affecting 2-3% of the adult general population, although other sources report a prevalence of up to 14%. It is one of the most common tongue disorders that occurs in children. The condition often starts in childhood, sometimes at an early age, but others report that the highest incidence occurs in the over 40 age group. Females are sometimes reported to be more commonly affected than males, in a 2:1 ratio, although others report that the gender distribution is equal.

Bacterial

- (Plaque-induced) gingivitis—A common periodontal (gum) disease is Gingivitis. Periodontal refers to the area the infection affects, which include the teeth, gums, and tissues surrounding the teeth. Bacteria cause inflammation of the gums which become red, swollen and can bleed easily. The bacteria along with mucus form a sticky colorless substance called plaque which harbours the bacteria. Plaque that is not removed by brushing and flossing hardens to form tartar that brushing doesn't clean. Smoking is a major risk factor. Treatment of gingivitis is dependent on how severe and how far the disease has progressed. If the disease is not too severe it is possible to treat it with chlorhexidine rinse and brushing with fluoride toothpaste to kill the bacteria and remove the plaque, but once the infection has progressed antibiotics may be needed to kill the bacteria.

- Periodontitis—When gingivitis is not treated it can advance to periodontitis, when the gums pull away from the teeth and form pockets that harbor the bacteria. Bacterial toxins and the body's natural defenses start to break down the bone and connective tissues. The tooth may eventually become loose and have to be removed.

- Scarlet fever is caused by streptococci species, and starts as tonsilitis and pharyngitis before involving the soft palate and the tongue. It usually occurs in children where a fever occurs and a rash develops on the skin. It is treated with penicillin and the prognosis is generally excellent.

Viral

- Herpes simplex (infection with herpes simplex virus, or HSV) is very common in the mouth and lips. This virus can cause blisters and sores around the mouth (herpetic gingivostomatitis) and lips (herpes labialis). HSV infections tend to recur periodically. Although many people get infected with the virus, only 10% actually develop the sores. The sores may last anywhere from 3–10 days and are very infectious. Some people have recurrences either in the same location or at a nearby site. Unless the individual has an impaired immune system, e.g., owing to HIV or cancer-related immune suppression, recurrent infections tend to be mild in nature and may be brought on by stress, sun, menstrual periods, trauma or physical stress.

- Mumps of the salivary glands is a viral infection of the parotid glands. This results in painful swelling at the sides of the mouth in both adults and children. The infection is quite contagious. Today mumps is prevented by getting vaccinated in infancy. There is no specific treatment for mumps except for hydration and painkillers. Sometimes mumps can cause inflammation of the brain, testicular swelling or hearing loss.

Fungal

- Oral candidiasis is by far the most common fungal infection that occurs in the mouth. It usually occurs in immunocompromised individuals. Individuals who have undergone a transplant, HIV, cancer or use corticosteroids commonly develop candida of the mouth and oral cavity. Other risk factors are dentures and tongue piercing. The typical signs are a white patch that may be associated with burning, soreness, irritation or a white cheesy like appearance. Once the diagnosis is made, candida can be treated with a variety of anti fungal drugs.

This is a common condition present in denture wearers. It appears as reddened but painless mucosa beneath the denture. 90% of cases are associated with Candidia species, and it is the most common form of oral candidiasis. Treatment is by antifungal medication and improved dental hygiene, such as not wearing the denture during sleep.

The name "lie bumps" is a result of a myth that telling lies would cause them. However, very little has been written about this condition in scientific articles or textbooks and scientific studies have failed to produce a definite cause. Possible causes include: "stress, gastrointestinal upset, menstruation, acidic or sour food, smoking, and local trauma" (direct physical irritation) of the tongue. Lie bumps are often caused by the taste bud(s) splitting.

These bumps are small, white bumps on the base of the tongue. They are likely to be the result of transient lingual papillitis (TLP). This condition is limited to the upper (dorsal) surface of the tongue, affecting some of the tiny bumps on the tongue known as the fungiform papillae, what we commonly call the "taste buds."

TLP is a harmless problem. These bumps can become notably red or white and are quite tender for up to several days. While the cause of TLP is not known with certainty, most experts feel that local accidental trauma (rubbing, scraping or biting) is a major factor; however, contact reactions to things like certain foods have also been suggested. Lie bumps are not contagious and the discomfort is relatively minor. Typically these lesions heal within a few days with no treatment, though a doctor may refer a patient to an oral pathologist in prolonged cases.

Crenated tongue (also called scalloped tongue, pie crust tongue, lingua indentata, or crenulated tongue) is a descriptive term for the appearance of the tongue when there are indentations along the lateral borders (the sides), as the result of compression of the tongue against the adjacent teeth.

The oral mucosa in the area of crenation is usually of normal color, but there may be erythema (redness) if exposed to a high degree of friction or pressure. Crenated tongue is usually asymptomatic and harmless.

It is not a disease as such, but usually results from habits where the tongue is pressed against the lingual surfaces (the side facing the tongue) of the dental arches, or from any cause of macroglossia (enlarged tongue), which in itself has many causes such as Down syndrome.

Where crenation is caused by parafunctional habits, there may also be associated bruxism, linea alba, or morsicatio buccarum.

Morsicatio buccarum (also termed chronic cheek biting and chronic cheek chewing) is a condition characterized by chronic irritation or injury to the buccal mucosa (the lining of the inside of the cheek within the mouth), caused by repetitive chewing, biting or nibbling.

Allergic contact stomatitis (also termed "allergic gingivostomatitis" or "allergic contact gingivostomatitis") is a type IV (delayed) hypersensitivity reaction that occurs in susceptible atopic individuals when allergens penetrate the skin or mucosa.

Allergens, which may be different for different individuals, combine with epithelial-derived proteins, forming haptens which bind with Langerhans cells in the mucosa, which in turn present the antigen on their surface to T lymphocytes, sensitizing them to that antigen and causing them to produce many specific clones. The second time that specific antigen is encountered, an inflammatory reaction is triggered at the site of exposure. Allergic contact stomatitis is less common than allergic contact dermatitis because the mouth is coated in saliva, which washes away antigens and acts as a barrier. The oral mucosa is also more vascular (has a better blood supply) than skin, meaning that any antigens are more quickly removed from the area by the circulation. Finally, there is substantially less keratin in oral mucosa, meaning that there is less likelihood that haptens will form.

Allergic contact stomatitis appears as non-specific inflammation, so it may be mistaken for chronic physical irritation. There may be burning or soreness of the mouth and ulceration. Chronic exposure to the allergen may result in a lichenoid lesion. Plasma cell gingivitis may also occur, which may be accompanied by glossitis and cheilitis.

Allergens that may cause allergic contact stomatitis in some individuals include cinnamaldehyde, Balsam of Peru, peppermint, mercury, gold, pyrophosphates, zinc citrate, free acrylic monomer, nickel, fluoride, and sodium lauryl sulfate. These allergens may originate from many sources, including various foods and drink, chewing gum, toothpaste, mouthwash, dental floss, dental fillings, dentures, orthodontic bands or wires, and many other sources. If the substance containing the allergen comes into contact with the lips, allergic contact cheilitis can occur, together with allergic contact stomatitis.

The diagnosis is confirmed by patch test, and management is by avoidance of exposure to the allergen.

BMS is fairly common worldwide, (however, other sources describe it as rare), and affects up to five individuals per 100,000 general population. People with BMS are more likely to be middle aged or elderly, and females are three to seven times more likely to have BMS than males. Some report a female to male ratio of as much as 33 to 1. BMS is reported in about 10-40% of women seeking medical treatment for menopausal symptoms, and BMS occurs in about 14% of postmenopausal women. Males and younger individuals of both sexes are sometimes affected.

Asian and Native American people have considerably higher risk of BMS.

Malnutrition, whether by malabsorption, or poor diet, especially hematinic deficiencies (iron, vitamin B12, folic acid) can predispose to oral candidiasis, by causing diminished host defense and epithelial integrity. For example, iron deficiency anemia is thought to cause depressed cell-mediated immunity. Some sources state that deficiencies of vitamin A or pyridoxine are also linked.

There is limited evidence that a diet high in carbohydrates predisposes to oral candidiasis. "In vitro" and studies show that Candidal growth, adhesion and biofilm formation is enhanced by the presence of carbohydrates such as glucose, galactose and sucrose.

Smoking, especially heavy smoking, is an important predisposing factor but the reasons for this relationship are unknown. One hypothesis is that cigarette smoke contains nutritional factors for "C. albicans", or that local epithelial alterations occur that facilitate colonization of candida species.

It is an uncommon condition, occurring with equal prevalence in males and females and at any age.

There are no specific treatments for this problem, other than using ice or numbing medicines to ease the pain.

In about 50% of cases of burning mouth sensation no identifiable cause is apparent, these cases are termed (primary) BMS. Several theories of what causes BMS have been proposed, and these are supported by varying degrees of evidence, but none is proven.

As most people with BMS are postmenopausal women, one theory of the cause of BMS is of estrogen or progesterone deficit, but a strong statistical correlation has not been demonstrated. Another theory is that BMS is related to autoimmunity, as abnormal antinuclear antibody and rheumatoid factor can be found in the serum of more than 50% of persons with BMS, but these levels may also be seen in elderly people who do not have any of the symptoms of this condition. Whilst salivary flow rates are normal and there are no clinical signs of a dry mouth to explain a complaint of dry mouth, levels of salivary proteins and phosphate may be elevated and salivary pH or buffering capacity may be reduced.

Depression and anxiety are strongly associated with BMS. It is not known if depression is a cause or result of BMS, as depression may develop in any setting of constant unrelieved irritation, pain, and sleep disturbance. It is estimated that about 20% of BMS cases involve psychogenic factors, and some consider BMS a psychosomatic illness, caused by cancerophobia, concern about sexually transmitted infections, or hypochondriasis.

Chronic low-grade trauma due to parafunctional habits (e.g. rubbing the tongue against the teeth or pressing it against the palate), may be involved. BMS is more common in persons with Parkinson's disease, so it has been suggested that it is a disorder of reduced pain threshold and increased sensitivity. Often people with BMS have unusually raised taste sensitivity, termed hypergeusia ("super tasters"). Dysgeusia (usually a bitter or metallic taste) is present in about 60% of people with BMS, a factor which led to the concept of a defect in sensory peripheral neural mechanisms. Changes in the oral environment, such as changes in the composition of saliva, may induce neuropathy or interruption of nerve transduction. The onset of BMS is often spontaneous, although it may be gradual. There is sometimes a correlation with a major life event or stressful period in life. In women, the onset of BMS is most likely three to twelve years following menopause.

It is a relatively common condition, with an estimated prevalence of 6.8%–11% amongst children. Males are more commonly affected. The condition may be seen at any age, but generally affects older people more frequently. The condition also generally becomes more accentuated with age. The prevalence of the condition increases significantly with age, occurring in 40% of the population after the age of 40.

Tongue diseases can be congenital or acquired, and are multiple in number. Considered according to a surgical sieve, some example conditions which can involve the tongue are discussed below. Glossitis is a general term for tongue inflammation, which can have various etiologies, e.g. infection.

Behavior therapy is important especially when the kids are in their primary dentition in the pre-adolescent age. Improving habits at this time may lead to self-correction of open bite in many cases. Sometimes presence of infantile swallowing into early childhood may lead to an anterior open bite in patients. Habit control through appliances such as Tongue crib or Tongue spurs may be used in adolescent ages if the behavior modification fails to stop the habit.