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.

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.

The histology of lichen nitidus is significant for a "...localized granulomatous lymphohistiocytic infiltrate in an expanded dermal papilla with thinning of overlying epidermis and downward extension of the ridges at the lateral margin of the infiltrate, producing a typical 'claw clutching a ball' picture..."

Linear arrangements of these papules is common (referred to as a Koebner phenomenon), especially on the forearms, but may occasionally be grouped, though not confluent, on flexural areas. Generally, the initial lesions are localized, and remain so, to the chest, abdomen, glans penis, and flexor aspects of the upper extremities; however, less commonly, the disease process can (1) be strictly isolated to the palms and soles, presenting with many hyperkeratotic, yellow papules that may coalesce into plaques that fissure or “...sometimes a non-specific keratoderma resembling chronic eczema,” or (2) become more widespread, with papules widely distributed on the body—the extensor surfaces of the elbows, wrists, and hands, folds of the neck, submammary region in females, groin, thighs, ankles, and feet—and fusing into erythematous, minimally scaled plaques, with reddness that develops tints of violet, brown, and yellow.

Lichen striatus is defined by:

The papules could be smooth, flat topped or scaly. The band of lichen striatus varies from a few millimeters to 1-- 2 cm wide and extends from a few centimeters to the complete length of the extremity. By and big, the papules are unilateral and single on an extremity along the lines of Blaschko.

Keratosis pilaris results in small bumps on the skin that feel like rough sandpaper. They are skin-colored bumps the size of a grain of sand, many of which are surrounded by a slight pink color in light skinned people and dark spots in dark skinned people. Most people with keratosis pilaris do not have symptoms but the bumps in the skin can occasionally be itchy.

Though people with keratosis pilaris experience the condition year-round, the problem can become exacerbated and the bumps are likely to look and feel more pronounced in color and texture during the colder months when moisture levels in the air are lower. The symptoms may also worsen during pregnancy or after childbirth.

People burdened with LSC report pruritus, followed by uncontrollable scratching of the same body region, excessively. Most common sites of LSC are the sides of the neck, the scalp, ankles, vulva, pubis, scrotum, and extensor sides of the forearms. However, due to the stigma associated with chronic scratching, some patients will not admit to chronic rubbing or abrasion. The skin may become thickened and hyperpigmented (lichenified) as a direct result of chronic exoriation. Typically this period of increased scratching is associated with stressors.

A papulosquamous disorder is a condition which presents with both papules and scales, or both scaly papules and plaques.

Examples include psoriasis, lichen planus, and pityriasis rosea.

Pityriasis amiantacea (also known as "Tinea amiantacea") is an eczematous condition of the scalp in which thick tenaciously adherent scale infiltrates and surrounds the base of a group of scalp hairs. It does not result in scarring or alopecia.

Pityriasis amiantacea was first described by Alibert in 1832. Pityriasis amiantacea affects the scalp as shiny asbestos-like (amiantaceus) thick scales attached in layers to the hair shaft. The scales surround and bind down tufts of hair. The condition can be localised or covering over the entire scalp. Temporary alopecia and scarring alopecia may occur due to repeated removal of hairs attached to the scale. It is a rare disease with a female predilection.

Pityriasis amiantacea can easily be misdiagnosed due its close resemblance to other scalp diseases such as psoriasis, seborrhoeic dermatitis or lichen planus. However in pityriasis amiantacea the scales are attached to both the hair shaft and the scalp. Pityriasis amiantacea may be present with other inflammatory conditions such as atopic dermatitis or seborrhoeic dermatitis and sebaceous scales and alopecia can occur. According to the dermatology text Bolognia this condition is most often seen in psoriasis, but may also be seen in secondarily infected atopic dermatitis, seborrheic dermatitis, and tinea capitis.

Erythroderma is generalized exfoliative dermatitis, which involves 90% or more of the patient's skin. The most common cause of erythroderma is exacerbation of an underlying skin disease, such as psoriasis, contact dermatitis, seborrheic dermatitis, lichen planus, pityriasis rubra pilaris or a drug reaction. Primary erythroderma is less frequent and is usually seen in cases of cutaneous T-cell lymphoma, in particular in Sézary's disease.

The most common causes of exfoliative dermatitis are best remembered by the mnemonic device ID-SCALP. The causes and their frequencies are as follows:

- Idiopathic - 30%

- Drug allergy - 28%

- Lymphoma and leukemia - 14%

- Atopic dermatitis - 10%

- Psoriasis - 8%

- Contact dermatitis - 3%

- Seborrheic dermatitis - 2%

Differential diagnosis in patients with erythroderma may be difficult.

Erythroderma (also known as "Exfoliative dermatitis," "Dermatitis exfoliativa") is an inflammatory skin disease with erythema and scaling that affects nearly the entire cutaneous surface.

In ICD-10, a distinction is made between "exfoliative dermatitis" at L26, and "erythroderma" at L53.9.

Keratosis pilaris (KP) (also follicular keratosis, lichen pilaris, or colloquially "chicken skin") is a common, autosomal dominant, genetic condition of the skin's hair follicles characterized by the appearance of rough, slightly red bumps on light skin and brown bumps on darker skin. It most often appears on the back, outer sides of the upper arm (though the forearm can also be affected), face, thighs, and buttocks; KP can also occur on the hands, and tops of legs, sides, or any body part except glabrous skin (like the palms or soles of feet). Often the lesions will appear on the face, which may be mistaken for acne.

LS can occur without symptoms. White patches on the LS body area, itching, pain, pain during sex (in genital LS), easier bruising, cracking, tearing and peeling, and hyperkeratosis are common symptoms in both men and women. In women, the condition most commonly occurs on the vulva and around the anus with ivory-white elevations that may be flat and glistening.

In males, the disease may take the form of whitish patches on the foreskin and its narrowing (preputial stenosis), forming an "indurated ring", which can make retraction more difficult or impossible. In addition there can be lesions, white patches or reddening on the glans. In contrast to women, anal involvement is less frequent. Meatal stenosis, making it more difficult or even impossible to urinate, may also occur.

On the non-genital skin, the disease may manifest as porcelain-white spots with small visible plugs inside the orifices of hair follicles or sweat glands on the surface. Thinning of the skin may also occur.

The bacteria staphylococci are present in the majority of cases. Treatment with systemic antibiotics and coal tar shampoo can completely clear the condition when Staphylococcus aureus bacteria are found. Fungal infections such as tinea capitis are known to mimic the symptoms of the condition and can be cleared with antifungal treatment.

Lichen aureus (also known as "lichen purpuricus") is a skin condition characterized by the sudden appearance of one or several golden or rust-colored, closely packed macules or lichenoid papules.

There are several types of pemphigus which vary in severity: pemphigus vulgaris, pemphigus foliaceus, Intraepidermal neutrophilic IgA dermatosis, and paraneoplastic pemphigus.

- Pemphigus vulgaris (PV - ICD-10 L10.0) is the most common form of the disorder and occurs when antibodies attack "Desmoglein 3". Sores often originate in the mouth, making eating difficult and uncomfortable. Although pemphigus vulgaris may occur at any age, it is most common among people between the ages of 40 and 60. It is more frequent among Ashkenazi Jews. Rarely, it is associated with myasthenia gravis. Nail disease may be the only finding and has prognostic value in management.

- Pemphigus foliaceus (PF) is the least severe of the three varieties. "Desmoglein 1", the protein that is destroyed by the autoantibody, is found in only the top dry layer of the skin. PF is characterized by crusty sores that often begin on the scalp, and may move to the chest, back, and face. Mouth sores do not occur. This form is also frequent among Ashkenazi Jews. It is not as painful as pemphigus vulgaris, and is often mis-diagnosed as dermatitis or eczema

- Intraepidermal neutrophilic IgA dermatosis is characterized histologically by intraepidermal bullae with neutrophils, some eosinophils, and acantholysis.

- The least common and most severe type of pemphigus is paraneoplastic pemphigus (PNP). This disorder is a complication of cancer, usually lymphoma and Castleman's disease. It may precede the diagnosis of the tumor. Painful sores appear on the mouth, lips, and the esophagus. In this variety of pemphigus, the disease process often involves the lungs, causing bronchiolitis obliterans (constrictive bronchiolitis). Though much less frequent, it is still found the most in the Ashkenazi Jewish population. Complete removal of and/or cure of the tumor may improve the skin disease, but lung damage is generally irreversible.

- Endemic pemphigus foliaceus, including the Fogo Selvagem, the new variant of endemic pemphigus folaiceus in El Bagre, Colombia, South America, and the Tunisian endemic pemphigus in North Africa.

Note that Hailey-Hailey disease, also called familial benign pemphigus, is an inherited (genetic) skin disease, not an autoimmune disease. It is therefore not considered part of the Pemphigus group of diseases.

Prurigo nodularis (PN), also known as nodular prurigo, is a skin disease characterised by pruritic (itchy) nodules which usually appear on the arms or legs. Patients often present with multiple excoriated lesions caused by scratching. PN is also known as Hyde prurigo nodularis, "Picker's nodules", atypical nodular form of neurodermatitis circumscripta, lichen corneus obtusus.

Lichen simplex chronicus is a distinct clinical entity.

Lichen simplex chronicus (LSC) (also known as "Neurodermatitis") is a skin disorder characterized by chronic itching and scratching. The constant scratching causes thick, leathery, darkened, (lichenified) skin. This condition is associated with many factors, including the scratch-itch cycle, psychological stressors, and atopy. LSC is more common between ages 35 and 50 and is seen approximately twice as often in women compared to men.

Lichen striatus (also known as blaschko linear acquired inflammatory skin eruption and linear lichenoid dermatosis) is a rare skin condition that is seen primarily in children, most frequently appearing ages 5–15. It consists of a self-limiting eruption of small, scaly papules.

Desquamative gingivitis involves lesions of the free and attached gingiva. Unlike plaque-induced inflammation of the gums (normal marginal gingivitis), desquamative gingivitis extends beyond the marginal gingiva, involving the full width of the gingiva and sometimes the alveolar mucosa. The term "full width gingivitis" usually refers to the oral lesions of orofacial granulomatosis however. The color is another dissimilarity between typical marginal gingivitis and desquamative gingivitis, in the latter it is dusky red. Plasma cell gingivitis is another form of gingivitis which affects both the attached and free gingiva.

Chronic and repetitive scratching, picking, or rubbing of the nodules may result in permanent changes to the skin, including nodular lichenification, hyperkeratosis, hyperpigmentation, and skin thickening. Unhealed, excoriated lesions are often scaly, crusted or scabbed. Many patients report a lack of wound healing even when medications relieve the itching and subsequent scratching.

Patients often:

- seek treatment during middle-age, although PN can occur at any age.

- have a history of chronic severe pruritus.

- have a significant medical history for unrelated conditions.

- suffer from liver or kidney dysfunctions.

- suffer secondary skin infections.

- have a personal or family history of atopic dermatitis.

- have other autoimmune disorders.

- have low vitamin D levels.

Distress due to the discomfort and pain of Lichen Sclerosus is normal, as are concerns with self-esteem and sex. Counseling can help.

According to the National Vulvodynia Association, which also supports women with Lichen Sclerosus, vulvo-vaginal conditions can cause feelings of isolation, hopelessness, low self-image, and much more. Some women are unable to continue working or have sexual relations and may be limited in other physical activities. Depression, anxiety, and even anger are all normal responses to the ongoing pain LS patients suffer from.

Desquamative gingivitis (DG) is an erythematous (red), desquamatous (shedding) and ulcerated appearance of the gums. It is a descriptive term and can be caused by several different disorders.

Papular mucinosis is chronic and may be progressive. The dermal layer of the skin breaks out into small and solid bumps, usually conical in shape and measured from 2 to 4 mm or sometimes flat-topped papules. Unlike pustules, these bumps do not contain pus. Instead they contain mucin, a substance of mucus, the body's natural and protective lubricant found in saliva and epithelial cells in lungs and the sensitive part of the nose. They usually come in clusters such as linear arrays. Less frequently, urticarial, nodular, or sometimes annular lesions may be appreciated. The dorsal aspect of the hands, face, elbows, and extensor portions of the extremities are most frequently affected. Mucosal lesions are absent. The coalescence of papules on the face, particularly on the glabella, results in longitudinal folding and gives the appearance of a leonine facies.

In scleromyxedema, symptoms can occur on larger part of the body. Erythema and scleroderma-like induration occurs on the skin. In addition, the mobility of the lips, hands, arms, and legs is reduced. Proximal myopathy, inflammatory polyarthritis, central nervous system symptoms, esophageal aperistalsis, and hoarseness are among the notable systemic symptoms. If viscera is involved, the disease will be fatal. The dermatoneuro syndrome is a rare neurological complication of the disease presenting with fever, seizures and altered mental status.

Pemphigus ( or ) is a rare group of blistering autoimmune diseases that affect the skin and mucous membranes. The name is derived from the Greek root "pemphix" meaning "pustule".

In pemphigus, autoantibodies form against desmoglein. Desmoglein forms the "glue" that attaches adjacent epidermal cells via attachment points called desmosomes. When autoantibodies attack desmogleins, the cells become separated from each other and the epidermis becomes "unglued", a phenomenon called acantholysis. This causes blisters that slough off and turn into sores. In some cases, these blisters can cover a significant area of the skin.

Originally, the cause of this disease was unknown, and "pemphigus" was used to refer to any blistering disease of the skin and mucosa. In 1964, researchers found that the blood of patients with pemphigus contained antibodies to the layers of skin that separate to form the blisters. In 1971, an article investigating the autoimmune nature of this disease was published.