This is a skin disorder characterized by a self-perpetuating scratch-itch cycle:

- It may begin with something that rubs, irritates, or scratches the skin, such as clothing.

- This causes the person to rub or scratch the affected area. Constant scratching causes the skin to thicken.

- The thickened skin itches, causing more scratching, causing more thickening.

- Affected area may spread rapidly through the rest of the body.

Many hypothesize LSC has a psychosomatic origin. Those predisposed to itch as a response to emotional tensions may be more susceptible to the itch-scratch cycle. It may also be associated with nervousness, anxiety, depression, and other psychological disorders. Many people with LSC are aware of the scratching they do during the day, but they might not be aware of the scratching they do in their sleep. LSC is also associated with atopy, or atopic dermatitis (eczema).

In contrast to cutaneous LP, which is self limited, lichen planus lesions in the mouth may persist for many years, and tend to be difficult to treat, with relapses being common. Atrophic/erosive lichen planus is associated with a small risk of cancerous transformation, and so people with OLP tend to be monitored closely over time to detect any potential change early. Sometimes OLP can become secondarily infected with Candida organisms.

Pemphigus foliaceus has been recognized in pet dogs, cats, and horses and is the most common autoimmune skin disease diagnosed in veterinary medicine. Pemphigus foliaceus in animals produces clusters of small vesicles that quickly evolve into pustules. Pustules may rupture, forming erosions or become crusted. Left untreated, pemphigus foliaceus in animals is life-threatening, leading to not only loss of condition but also secondary infection.

Pemphigus vulgaris is a very rare disorder described in pet dogs and cats. Paraneoplastic pemphigus has been identified in pet dogs.

Lichen sclerosus may have a genetic component. Higher rates of lichen sclerosus have been reported among twins and among family members.

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.

In 2016, interferon gamma/CXCL10 axis was hypothesized to be a target for treatments that reverse inflammation. Apremilast is undergoing investigation as a potential treatment .

Although it is not clear what causes LS, several theories have been postulated. Lichen Sclerosus is not contagious; it cannot be caught from another person.

Several risk factors have been proposed, including autoimmune diseases, infections and genetic predisposition. There is evidence that LS can be associated with thyroid disease.

A 2003 survey of diseases of the foot in 16 European countries found onychomycosis to be the most frequent fungal foot infection and estimates its prevalence at 27%. Prevalence was observed to increase with age. In Canada, the prevalence was estimated to be 6.48%. Onychomycosis affects approximately one-third of diabetics and is 56% more frequent in people suffering from psoriasis.

The classification of exfoliative dermatitis into Wilson-Brocq (chronic relapsing), Hebra or pityriasis rubra (progressive), and Savill (self-limited) types may have had historical value, but it currently lacks pathophysiologic or clinical utility.

Worldwide, KP affects an estimated 30-50% of the adult population and approximately 50-80% of all adolescents. It is more common in women than in men, and is often present in otherwise healthy individuals. The skin condition is prevalent in persons of all ethnicities. No particular ethnicity is at higher risk for developing keratosis pilaris. Although keratosis pilaris may manifest in persons of any age, it usually appears within the first decade of life and is more common in young children. In most cases, the condition gradually improves before age 30, however it can persist longer.

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.

Rosin, the material commonly used to wax string instruments is known to cause allergic contact dermatitis in musicians. Nickel, a metal found in musical instruments causes allergic contact dermatitis on the fingers and hands of string instrumentalists and in the lip and neck of wind instrumentalists. Wind instrumentalists with lip and neck infection should switch to gold or plastic mouthpieces if allergic dermatitis occurs. (R)-4-methoxydalbergione present in rosewood may cause allergic contact dermatitis in violinists. Cane reed (causing chelitis in saxophone players), propolis (a wax used to close structural gaps in musical instruments), paraphenylenediamine (used to polish musical instruments) and potassium dichromate (tanning agent to the skin of the harp) also cause allergic contact dermatitis in musicians.

Following effective treatment recurrence is common (10–50%).

Nail fungus can be painful and cause permanent damage to nails. It may lead to other serious infections if the immune system is suppressed due to medication, diabetes or other conditions. The risk is most serious for people with diabetes and with immune systems weakened by leukemia or AIDS, or medication after organ transplant. Diabetics have vascular and nerve impairment, and are at risk of cellulitis, a potentially serious bacterial infection; any relatively minor injury to feet, including a nail fungal infection, can lead to more serious complications. Infection of the bone is another rare complication.

Frequent, chronic contact of instruments to skin may make it callous by the thickening of stratum corneum. Use of 'thumb position' in cellists may cause callosity of left thumb. Garrod's pads are seen on the dorsal left second and third fingers over the proximal interphalangeal joints in violinists. Drummer's digit is the callosity seen on the lateral phalynx of the left finger. Callosities need treatment only when they are excessive or symptomatic.

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.

Keratosis pilaris occurs when the human body produces excess amounts of the skin protein keratin, resulting in the formation of small, raised bumps in the skin often with surrounding redness. The excess keratin, which is the color of the person's natural skin tone, surrounds and entraps the hair follicles in the pore. This causes the formation of hard plugs (process known as hyperkeratinization). Many KP bumps contain an ingrown hair that has coiled. This is a result of the keratinized skin's "capping off" the hair follicle, preventing the hair from exiting. The hair grows encapsulated inside the follicle. KP is more common in patients affected by atopic diseases such as allergic rhinitis and atopic dermatitis.

Fiddler’s neck does not usually form unless the musician is practicing or playing for more than a few hours each day, and only seems to develop after a few years of serious playing. Thus, when not infected or otherwise problematic, fiddler’s neck may be known as a benign practice mark and may be worn proudly as an indication of long hours of practice. Blum & Ritter (1990) found that 62% of 523 professional violinists and violists in West Germany experienced fiddler’s neck, with the percentage among violists being higher (67%) than among violinists (59%). Viola players are believed to be more predisposed to developing fiddler’s neck than violinists because the viola is larger and heavier, but this has not been empirically confirmed.

The development of fiddler’s neck does not depend on preexisting skin problems, and Blum & Ritter find that only 23% of men and 14% of women in their study reported cutaneous disorders in other parts of the face (mainly acne and eczema) that were independent of playing the violin or viola. Fiddler’s neck may exacerbate existing acne, but acne may also be limited solely to the lesion and not appear elsewhere. Nonetheless, musicians with underlying dermatologic diseases like acne and eczema are more endangered by fiddler’s neck than others. Males may develop folliculitis or boils due to involvement of beard hair.

The cause of prurigo nodularis is unknown, although other conditions may induce PN. PN has been linked to Becker's nevus, linear IgA disease, an autoimmune condition, liver disease and T cells. Systemic pruritus has been linked to cholestasis, thyroid disease, polycythaemia rubra vera, uraemia, Hodgkins disease, HIV and other immunodeficiency diseases. Internal malignancies, liver failure, renal failure, and psychiatric illnesses have been considered to induce PN, although more recent research has refuted a psychiatric cause for PN. Patients report an ongoing battle to distinguish themselves from those with psychiatric disorders such as delusions of parasitosis and other psychiatric conditions.

Generally, lichen nitidus is asymptomatic and self-limited; therefore, no treatment is required. However, if persistent pruritus is present, or the appearance “...interferes with daily activities or outlook...” topical glucocorticoids may be tried. If the disease process is symptomatic, generalized and extensive, oral glucocorticoids may be indicated. Other reported treatments include PUVA, UVA/UVB phototherapy, astemizole, acitretin, and etretinate.

When appears with sun/humidity; air conditioning (cool dry air) reduces swelling and discomfort.

Lichen nitidus is a chronic inflammatory disease of unknown cause characterized by 1–2 mm, discrete and uniform, shiny, flat-topped, pale flesh-colored or reddish-brown papules that may appear as hypopigmented against dark skin. Occasionally, minimal scaling is present or can be induced by rubbing the surface of the papules. The disease usually affects children and young adults and is painless and usually nonpruritic, although protracted itching may occur in some cases. It is sometimes referred to by dermatologists as "mini lichen planus".

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.

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.

All of these drugs may cause severe side effects, so the patient should be closely monitored by doctors. Once the outbreaks are under control, dosage is often reduced, to lessen side effects.

If skin lesions do become infected, antibiotics may be prescribed. Tetracycline antibiotics have a mildly beneficial effect on the disease and are sometimes enough for Pemphigus Foliaceus. In addition, talcum powder is helpful to prevent oozing sores from adhering to bedsheets and clothes. Wound care and treatment is often akin to that used in burn units, including careful use of dressings that don't stick to the wounds, etc.

If paraneoplastic pemphigus is diagnosed with pulmonary disease, a powerful cocktail of immune suppressant drugs is sometimes used in an attempt to halt the rapid progression of bronchiolitis obliterans, including methylprednisolone, ciclosporin, azathioprine, and thalidomide. Plasmapheresis may also be useful.

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.

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.