AC almost always affects the lower lip and only rarely the upper lip, probably because the lower lip is more exposed to the sun. In the unusual cases reported where it affects the upper lip, this may be due to upper lip prominence. The commissures (corners of the mouth) are not usually involved.

Affected individuals may experience symptoms such as a dry sensation and cracking of the lips.

It is usually painless and persistent.

The appearance is variable. White lesions indicate hyperkeratosis. Red, erosiive or ulcerative lesions indicate atrophy, loss of epithelium and inflammation. Early, acute lesions may be erythematous (red) and edematous (swollen). With months and years of sun exposure, the lesion becomes chronic and may be grey-white in color and appear dry, scaly and wrinkled.

There is thickening whitish discoloration of the lip at the border of the lip and skin. There is also a loss of the usually sharp border between the red of the lip and the normal skin, known as the vermillion border. The lip may become scaly and indurated as AC progresses.

When palpated, the lip may have a texture similar to rubbing the gloved finger along sandpaper.

AC may occur with skin lesions of actinic keratosis or skin cancer elsewhere, particularly on the head and neck since these are the most sun exposed areas. Rarely it may represent a genetic susceptibility to light damage (e.g. xeroderma pigmentosum or actinic prurigo).

Actinic cheilitis (abbreviated to AC, also termed actinic cheilosis, actinic keratosis of lip, solar cheilosis, sailor's lip, farmer's lip), is cheilitis (lip inflammation) caused by long term sunlight exposure. Essentially it is a burn, and a variant of actinic keratosis which occurs on the lip. It is a premalignant condition, as it can develop into squamous cell carcinoma (a type of mouth cancer).

Plasma cell cheilitis is a very rare presentation of a condition which more usually occurs on the gingiva (termed "plasma cell gingivitis") or sometimes the tongue. Plasma cell cheilitis appears as well defined, infiltrated, dark red plaque with a superficial lacquer-like glazing. Plasma cell cheilitis usually involves the lower lip. The lips appear dry, atrophic and fissured. Angular cheilitis is sometimes also present.

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.

Actinic keratoses ("AKs") most commonly present as a white, scaly plaque of variable thickness with surrounding redness; they are most notable for having a sandpaper-like texture when felt with a gloved hand. Skin nearby the lesion often shows evidence of solar damage characterized by notable pigmentary alterations, being yellow or pale in color with areas of hyperpigmentation; deep wrinkles, coarse texture, purpura and ecchymoses, dry skin, and scattered telangiectasias are also characteristic. Photoaging leads to an accumulation of oncogenic changes, resulting in a proliferation of mutated keratinocytes that can manifest as AKs or other neoplastic growths. With years of sun damage, it is possible to develop multiple AKs in a single area on the skin.

The lesions are usually asymptomatic, but can be tender, itch, bleed, or produce a stinging or burning sensation. AKs are typically graded in accordance with their clinical presentation: Grade I (easily visible, slightly palpable), Grade II (easily visible, palpable), and Grade III (frankly visible and hyperkeratotic).

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.

Actinic keratoses can have various clinical presentations, often characterized as follows:

- Classic (or common): Classic AKs present as white, scaly macules, papules or plaques of various thickness, often with surrounding erythema. They are usually 2-6mm in diameter but can sometimes reach several centimeters in diameter.

- Hypertrophic (or hyperkeratotic): Hypertrophic AKs (HAKs) appear as a thicker scale or rough papule or plaque, often adherent to an erythematous base. Classic AKs can progress to become HAKs, and HAKs themselves can be difficult to distinguish from malignant lesions.

- Atrophic: Atrophic AKs lack an overlying scale, and therefore appear as a nonpalpable change in color (or macule). They are often smooth and red, and are less than 10mm in diameter.

- AK with cutaneous horn: A cutaneous horn is a keratinic projection with its height at least one-half of its diameter, often conical in shape. They can be seen in the setting of actinic keratosis as a progression of an HAK, but are also present in other skin conditions. 38–40% of cutaneous horns represent AKs.

- Pigmented AK: Pigmented AKs are rare variants that often present as macules or plaques that are tan to brown in color. They can be difficult to distinguish from a solar lentigo or lentigo maligna.

- Actinic cheilitis: When an AK forms on the lip, it is called actinic cheilitis. This usually presents as a rough, scaly patch on the lip, often accompanied by the sensation of dry mouth and symptomatic splitting of the lips.

- Bowenoid AK: Usually presents as a solitary, erythematous, scaly patch or plaque with well-defined borders. Bowenoid AKs are differentiated from Bowen's disease by degree of epithelial involvement as seen on histology.

The presence of ulceration, nodularity, or bleeding should raise concern for malignancy. Specifically, clinical findings suggesting an increased risk of progression to squamous cell carcinoma can be recognized as "IDRBEU": I (induration /inflammation), D (diameter > 1 cm), R (rapid enlargement), B (bleeding), E (erythema) and U (ulceration). AKs are usually diagnosed clinically, but because they are difficult to clinically differentiate from squamous cell carcinoma, any concerning features warrant biopsy for diagnostic confirmation.

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.

Common causes of drug-related cheilitis include Etretinate, Indinavir, Protease inhibitors, Vitamin A and Isotretinoin (a retinoid drug). Uncommon causes include Atorvastatin, Busulphan, Clofazimine, Clomipramine, Cyancobalamin, Gold, Methyldopa, Psoralens, Streptomycin, Sulfasalazine and Tetracycline. A condition called "drug-induced ulcer of the lip" is described as being characterized by painful or tender, well-defined ulcerations of the lip without induration. It is the result of oral administration of drugs, and the condition resolves when the drugs are 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.

Angular cheilitis is a fairly non specific term which describes the presence of an inflammatory lesion in a particular anatomic site (i.e. the corner of the mouth). As there are different possible causes and contributing factors from one person to the next, the appearance of the lesion is somewhat variable. The lesions are more commonly symmetrically present on both sides of the mouth, but sometimes only one side may be affected. In some cases, the lesion may be confined to the mucosa of the lips, and in other cases the lesion may extend past the vermilion border (the edge where the lining on the lips becomes the skin on the face) onto the facial skin. Initially, the corners of the mouth develop a gray-white thickening and adjacent erythema (redness). Later, the usual appearance is a roughly triangular area of erythema, edema (swelling) and breakdown of skin at either corner of the mouth. The mucosa of the lip may become fissured (cracked), crusted, ulcerated or atrophied. There is not usually any bleeding. Where the skin is involved, there may be radiating rhagades (linear fissures) from the corner of the mouth. Infrequently, the dermatitis (which may resemble eczema) can extend from the corner of the mouth to the skin of the cheek or chin. If "Staphylococcus aureus" is involved, the lesion may show golden yellow crusts. In chronic angular cheilitis, there may be suppuration (pus formation), exfoliation (scaling) and formation of granulation tissue.

Sometimes contributing factors can be readily seen, such as loss of lower face height from poorly made or worn dentures, which results in mandibular overclosure ("collapse of jaws"). If there is a nutritional deficiency underlying the condition, various other signs and symptoms such as glossitis (swollen tongue) may be present. In people with angular cheilitis who wear dentures, often there may be erythematous mucosa underneath the denture (normally the upper denture), an appearance consistent with denture-related stomatitis. Typically the lesions give symptoms of soreness, pain, pruritus (itching) or burning or a raw feeling.

Disseminated superficial actinic porokeratosis (DSAP) is a non-contagious skin condition with apparent genetic origin in the SART3 gene. It most often presents in sun-exposed areas of the body. Some DSAP cases have been reported in patients with acute immune compromised situations, particularly in the elderly. For those with sun damaged skin, the lesions usually begin to appear in the patient's 20s and increase in number and visibility in the 40s or 50s. Commonly, though not always, the number and visibility of lesions is in direct proportion to the amount of sun damage to the affected area.

Lesions generally are characterized by an irregularly shaped thread-like ring that is usually the size of a pencil eraser, though lesions vary and may be half or double that size. The thread-like ring is very thin, much like fabric thread for sewing, and raised such that it is both palpable and visible. The interior of the ring may be rough like sandpaper, or smooth. The interior is often discolored, though colors vary from patient to patient. Lesions, due to their vascular nature, can also vary according to body temperature, environmental temperatures, and other external stimuli. The internal ring color is most often reddish, purplish, pink, or brown.

Some patients report itching and irritation associated with the condition, and many report no notable sensation. Although no known hormonal link has been found, DSAP occurs more commonly in women.

A study in 2000 was done on a Chinese family, in which a locus for a gene was located.

The Newton classification divides denture-related stomatitis into three types based on severity. Type one may represent an early stage of the condition, whilst type two is the most common and type three is uncommon.

- Type 1 - Localized inflammation or pinpoint hyperemia

- Type 2 - More diffuse erythema (redness) involving part or all of the mucosa which is covered by the denture

- Type 3 - Inflammatory nodular/papillary hyperplasia usually on the central hard palate and the alveolar ridge

Despite the alternative name for this condition, "denture sore mouth", it is usually painless and asymptomatic. The appearance of the involved mucosa is erythematous (red) and edematous (swollen), sometimes

with petechial hemorrhage (pin-points of bleeding). This usually occurs beneath an upper denture. Sometimes angular cheilitis can coexist, which is inflammation of the corners of the mouth, also often associated with "Candida albicans". Stomatitis rarely develops under a lower denture. The affected mucosa is often sharply defined, in the shape of the covering denture.

22% of cases of angular cheilitis are due to irritants. Saliva contains digestive enzymes, which may have a degree of digestive action on tissues if they are left in contact. The corner of the mouth is normally exposed to saliva more than any other part of the lips. Reduced lower facial height (vertical dimension or facial support) is usually caused by edentulism (tooth loss), or wearing worn down, old dentures or ones which are not designed optimally. This results in overclosure of the mandible (collapse of the jaws), which extenuates the angular

skin folds at the corners of the mouth, in effect creating an intertriginous skin crease. The tendency of saliva to pool in these areas is increased, constantly wetting the area, which may cause tissue maceration and favors the development of a yeast infection. As such, angular cheilitis is more commonly seen in edentulous people (people without any teeth). It is by contrast uncommon in persons who retain their natural teeth. Angular cheilitis is also commonly seen in denture wearers. Angular cheilitis is present in about 30% of people with denture-related stomatitis. It is thought that reduced vertical dimension of the lower face may be a contributing factor in up to 11% of elderly persons with angular cheilitis and in up to 18% of denture wearers who have angular cheilitis. Reduced vertical dimension can also be caused by tooth migration, wearing orthodontic appliances, and elastic tissue damage caused by ultraviolet light exposure and smoking.

Habits or conditions that keep the corners of the mouth moist might include chronic lip licking, thumb sucking (or sucking on other objects such as pens, pipes, lollipops), dental cleaning (e.g. flossing), chewing gum, hypersalivation, drooling and mouth breathing. Some consider habitual lip licking or picking to be a form of nervous tic, and do not consider this to be true angular cheilitis, instead calling it "perlèche" (derived from the French word "pourlècher" meaning "to lick one’s lips"), or "factitious cheilitis" is applied to this habit. The term "cheilocandidiasis" describes exfoliative (flaking) lesions of the lips and the skin around the lips, and is caused by a superficial candidal infection due to chronic lip licking. Less severe cases occur during cold, dry weather, and is a form of chapped lips. Individuals may lick their lips in an attempt to provide a temporary moment of relief, only serving to worsen the condition.

The sunscreen in some types of lip balm degrades over time into an irritant. Using expired lipbalm can initiate mild angular cheilitis, and when the person applies more lipbalm to alleviate the cracking, it only aggravates it. Because of the delayed onset of contact dermatitis and the recovery period lasting days to weeks, people typically do not make the connection between the causative agent and the symptoms.

Porokeratosis is a specific disorder of keratinization that is characterized histologically by the presence of a cornoid lamella, a thin column of closely stacked, parakeratotic cells extending through the stratum corneum with a thin or absent granular layer.

This refers to a group of rare syndromes characterized by chronic candidal lesions on the skin, in the mouth and on other mucous membranes (i.e., a secondary oral candidiasis). These include Localized chronic mucocutaneous candidiasis, diffuse mucocutaneous candidiasis (Candida granuloma), candidiasis–endocrinopathy syndrome and candidiasis thymoma syndrome. About 90% of people with chronic mucocutaneous candidiasis have candidiasis in the mouth.

Geographic tongue, also termed benign migratory glossitis, is a common condition which usually affects the dorsal surface of the tongue. It is characterized by patches of depapillation and erythema bordered by a whitish peripheral zone. These patches give the tongue the appearance of a map, hence the name. Unlike glossitis due to nutritional deficiencies and anemia, the lesions of geographic tongue move around the tongue over time. This is because in geographic tongue, new areas of the tongue become involved with the condition whilst previously affected areas heal, giving the appearance of a moving lesion. The cause is unknown, and there is no curative treatment. Rarely are there any symptoms associated with the lesions, but occasionally a burning sensation may be present, which is exacerbated by eating hot, spicy or acidic foodstuffs. Some consider geographic tongue to be an early stage of fissured tongue, since the two conditions often occur in combination.

AP is characterized by itchy, inflamed papules, nodules, and plaques on the skin. Lesions typically appear hours or days after exposure of the skin to UV light, and follow a general pattern of sun-exposed areas. The face, neck, arms, hands, and legs are often affected, although lesions sometimes appear on skin that is covered by clothing and thus not exposed to UV light, thus making AP somewhat difficult to diagnose.

AP is a chronic disease, and symptoms usually worsen in the spring and summer as the day lengthens and exposure to sunlight increases.

Porokeratosis may be divided into the following clinical types:

- "Plaque-type porokeratosis" (also known as "Classic porokeratosis" and "Porokeratosis of Mibelli") is characterized by skin lesions that start as small, brownish papules that slowly enlarge to form irregular, annular, hyperkeratotic or verrucous plaques. Sometimes they may show gross overgrowth and even horn-like structures may develop. Skin malignancy, although rare, is reported from all types of porokeratosis. Squamous cell carcinomata have been reported to develop in Mibelli's type porokeratosis over partianal areas involving anal mucosa. This was the first report mentioning mucosal malignancy in any form of porokeratosis.

- "Disseminated superficial porokeratosis" is a more generalized processes and involves mainly the extremities in a bilateral, symmetric fashion. In about 50% of cases, skin lesions only develop in sun-exposed areas, and this is referred to as "disseminated superficial actinic porokeratosis"

- "Porokeratosis palmaris et plantaris disseminata" is characterized by skin lesions that are superficial, small, relatively uniform, and demarcated by a distinct peripheral ridge of no more than 1mm in height.

- "Linear porokeratosis" is characterized clinically skin lesions are identical to those of classic porokeratosis, including lichenoid papules, annular lesions, hyperkeratotic plaques with central atrophy, and the characteristic peripheral ridge.

- "Punctate porokeratosis" is a skin condition associated with either classic porokeratosis or linear porokeratosis types of porokeratosis, and is characterized by multiple, minute, and discrete punctate, hyperkeratotic, seed-like skin lesions surrounded by a thin, raised margin on the palms and soles.

- "Porokeratosis plantaris discreta" is a skin condition that occurs in adults, with a 4:1 female preponderance, characterized by a sharply marginated, rubbery, wide-based papules. It is also known as "Steinberg's lesion". It was characterized in 1970.

Actinic elastosis, also known as solar elastosis, is an accumulation of abnormal elastin (elastic tissue) in the dermis of the skin, or in the conjunctiva of the eye, which occurs as a result of the cumulative effects of prolonged and excessive sun exposure, a process known as photoaging.

This condition is characterized by a persistent erythematous, rhomboidal depapillated lesion in the central area of the dorsum of the tongue, just in front of the circumvallate papillae. Median rhomboid glossitis is a type of oral candidiasis, and rarely causes any symptoms. It is treated with antifungal medication. Predisposing factors include use of corticosteroid sprays or inhalers or immunosuppression.

Actinic elastosis usually appears as thickened, dry, wrinkled skin. Several clinical variants have been recorded. One of the most readily identifiable is the thickened, deeply fissured skin seen on the back of the chronically sun-exposed neck, known as cutis rhomboidalis nuchae. These features are a part of the constellation of changes that are seen in photoaged skin.

Keratosis (from "keratinocyte", the prominent cell type in the epidermis, and , abnormal) is a growth of keratin on the skin or on mucous membranes. More specifically, it can refer to:

- actinic keratosis (also known as solar keratosis)

- hydrocarbon keratosis

- keratosis pilaris (KP, also known as follicular keratosis)

- seborrheic keratosis

Actinic keratoses are pre-malignant growths. Seborrheic keratoses are not pre-malignant.

The clinical appearance is considerably varied in both the orientation, number, depth and length of the fissure pattern. There are usually multiple grooves/furrows 2–6 mm in depth present. Sometimes there is a large central furrow, with smaller fissures branching perpendicularly. Other patterns may show a mostly dorsolateral position of the fissures (i.e. sideways running grooves on the tongue's upper surface). Some patients may experience burning or soreness.