Psoriatic nails are characterized by a translucent discolouration in the nail bed that resembles a drop of oil beneath the nail plate. Early signs that may accompany the "oil drop" include thickening of the lateral edges of the nail bed with or without resultant flattening or concavity of the nail; separation of the nail from the underlying nail bed, often in thin streaks from the tip-edge to the cuticle; sharp peaked "roof-ridge" raised lines from cuticle to tip; or separation of superficial layers of the nail followed by loss of patches of these superficial layers, leaving thin red nails beneath; or nail pitting–punctate changes along the nail plate surface.

Psoriatic onychodystrophy or psoriatic nails is a nail disease. It is common in those suffering from psoriasis, with reported incidences varying from 10% to 78%. Elderly patients and those with psoriatic arthritis are more likely to have psoriatic nails.

GPP presents as pustules and plaques over a wide area of the body. It differs from the localized form of pustular psoriasis in that patients are often febrile and systemically ill.

However, the most prominent symptom, as described in the "Archives of Dermatology", is “sheeted, pinhead-sized, sterile, sub-corneal pustules”. The IPC roundtable adds that these pustules often occur either at the edges “of expanding, intensely inflammatory plaques” or “within erythrodermic skin.”

Von Zumbusch psoriasis is named after the German dermatologist Leo Ritter von Zumbusch (1874–1940), son of Kaspar von Zumbusch who described the first documented case of generalized pustular psoriasis in the early 1900s. See Case Report #1.

Sometimes all or any of GPP is referred to as von Zumbusch psoriasis, but in the literature it is often distinguished as one specific form of GPP.

Eugene M. Farber, MD and colleagues provide a description of von Zumbusch psoriasis in "Pustular Psoriasis", published in "Cutis". They describe the pattern as having “waves of widespread or universally fiery redness”. The affected areas are “painful and tender”. Small sub-corneal pustules form, with sizes originally between 1 and 10 mm in diameter. These pustules may merge to form “yellow-green lakes of pus”. The pustules dry out, and “Waves of scarlatiniform [resembling scarlet fever] peeling follow, removing the desiccating pustules”. In regards to the onset, the von Zumbusch form may “supervene on any previous pattern of psoriasis”. It also may or may not recur periodically.

Seborrheic-like psoriasis is a common form of psoriasis with clinical aspects of psoriasis and seborrheic dermatitis, and it may be difficult to distinguish from the latter. This form of psoriasis typically manifests as red plaques with greasy scales in areas of higher sebum production such as the scalp, forehead, skin folds next to the nose, skin surrounding the mouth, skin on the chest above the sternum, and in skin folds.

Psoriasis in the mouth is very rare, in contrast to lichen planus, another common papulosquamous disorder that commonly involves both the skin and mouth. When psoriasis involves the oral mucosa (the lining of the mouth), it may be asymptomatic, but it may appear as white or grey-yellow plaques. Fissured tongue is the most common finding in those with oral psoriasis and has been reported to occur in 6.5–20% of people with psoriasis affecting the skin. The microscopic appearance of oral mucosa affected by geographic tongue (migratory stomatitis) is very similar to the appearance of psoriasis. However, modern studies have failed to demonstrate any link between the two conditions.

Psoriatic erythroderma (also known as erythrodermic psoriasis) represents a generalized form of psoriasis that affects all body sites, including the face, hands, feet, nails, trunk, and extremities. First-line treatments for psoriatic erythroderma include immunosuppressive medications such as methotrexate, acitretin, or ciclosporin.

Longitudinal erythronychia presents with longitudinal red bands in the nail plate that commence in the matrix and extend to the point of separation of the nail plate and nailbed, and may occur on multiple nails with inflammatory conditions such as lichen planus or Darier's disease.

Longitudinal leukonychia is far less common and features smaller 1mm white longitudinal lines visible under the nail plate. It may be associated with Darier's disease.

Trachyonychia, sometimes called sandpapered nails, is a condition characterized by rough accentuated linear ridges (longitudinal striations) on the nails of the fingers and toes. When the condition occurs on all the twenty nails of the fingers and toes, it is known as twenty-nail dystrophy, most evident in childhood, favoring males.

Trachyonychia causes the nails to become opalescent, thin, dull, fragile, and finely longitudinally ridged, and, as a result, distally notched. It can be a manifestation of lichen planus, psoriasis, alopecia areata, immunoglobulin A deficiency, atopic dermatitis, and ichthyosis vulgaris.

"The longitudinal striations can occur as a normal part of the aging process", and not until the nails start to thin and get a sandpaper look is the condition called trachonychia. The nails are opalescent and frequently are brittle and split at the free margin. There has been evidence of the condition as a cutaneous manifestation of lichen planus. It has also been associated with other diseases such as eczema, psoriasis, alopecia areata, and atopic dermatitis. Trachonychia is often seen in vitiligo patients – suggesting that they are more susceptible to this condition.

Onychauxis presents with thickened nails without deformity, and this simple thickening may be the result of trauma, acromegaly, Darier's disease, psoriasis, or pityriasis rubra pilaris, or, in some cases, hereditary.

Also known as "true" leukonychia, this is the most common form of leukonychia, in which small white spots appear on the nails. Picking and biting of the nails are a prominent cause in young children and nail biters. Besides parakeratosis, air that is trapped between the cells may also cause this appearance. It is also caused by trauma. In most cases, when white spots appear on a single or a couple of fingers or toes, the most common cause is injury to the base (matrix) of the nail. When this is the case, white spots disappear after around eight months, which is the amount of time necessary for nails to regrow completely. The pattern and number of spots may change as the nail grows.

The most common symptom of a fungal nail infection is the nail becoming thickened and discoloured: white, black, yellow or green. As the infection progresses the nail can become brittle, with pieces breaking off or coming away from the toe or finger completely. If left untreated, the skin underneath and around the nail can become inflamed and painful. There may also be white or yellow patches on the nailbed or scaly skin next to the nail, and a foul smell. There is usually no pain or other bodily symptoms, unless the disease is severe. People with onychomycosis may experience significant psychosocial problems due to the appearance of the nail, particularly when fingers – which are always visible – rather than toenails are affected.

Dermatophytids are fungus-free skin lesions that sometimes form as a result of a fungus infection in another part of the body. This could take the form of a rash or itch in an area of the body that is not infected with the fungus. Dermatophytids can be thought of as an allergic reaction to the fungus.

Onychomycosis, also known as tinea unguium, is a fungal infection of the nail. This condition may affect toenails or fingernails, but toenail infections are particularly common.

Treatment may be based on the signs. Treatment may be with the medication terbinafine.

It occurs in about 10 percent of the adult population. It is the most common disease of the nails and constitutes about half of all nail abnormalities.

The term is from Ancient Greek ὄνυξ "ónux" "nail", μύκης "múkēs" "fungus" and -ωσις "ōsis" "functional disease."

Many conditions affect the human integumentary system—the organ system covering the entire surface of the body and composed of skin, hair, nails, and related muscle and glands. The major function of this system is as a barrier against the external environment. The skin weighs an average of four kilograms, covers an area of two square meters, and is made of three distinct layers: the epidermis, dermis, and subcutaneous tissue. The two main types of human skin are: glabrous skin, the hairless skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin. Within the latter type, the hairs occur in structures called pilosebaceous units, each with hair follicle, sebaceous gland, and associated arrector pili muscle. In the embryo, the epidermis, hair, and glands form from the ectoderm, which is chemically influenced by the underlying mesoderm that forms the dermis and subcutaneous tissues.

The epidermis is the most superficial layer of skin, a squamous epithelium with several strata: the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. Nourishment is provided to these layers by diffusion from the dermis, since the epidermis is without direct blood supply. The epidermis contains four cell types: keratinocytes, melanocytes, Langerhans cells, and Merkel cells. Of these, keratinocytes are the major component, constituting roughly 95 percent of the epidermis. This stratified squamous epithelium is maintained by cell division within the stratum basale, in which differentiating cells slowly displace outwards through the stratum spinosum to the stratum corneum, where cells are continually shed from the surface. In normal skin, the rate of production equals the rate of loss; about two weeks are needed for a cell to migrate from the basal cell layer to the top of the granular cell layer, and an additional two weeks to cross the stratum corneum.

The dermis is the layer of skin between the epidermis and subcutaneous tissue, and comprises two sections, the papillary dermis and the reticular dermis. The superficial papillary dermis with the overlying rete ridges of the epidermis, between which the two layers interact through the basement membrane zone. Structural components of the dermis are collagen, elastic fibers, and ground substance. Within these components are the pilosebaceous units, arrector pili muscles, and the eccrine and apocrine glands. The dermis contains two vascular networks that run parallel to the skin surface—one superficial and one deep plexus—which are connected by vertical communicating vessels. The function of blood vessels within the dermis is fourfold: to supply nutrition, to regulate temperature, to modulate inflammation, and to participate in wound healing.

The subcutaneous tissue is a layer of fat between the dermis and underlying fascia. This tissue may be further divided into two components, the actual fatty layer, or panniculus adiposus, and a deeper vestigial layer of muscle, the panniculus carnosus. The main cellular component of this tissue is the adipocyte, or fat cell. The structure of this tissue is composed of septal (i.e. linear strands) and lobular compartments, which differ in microscopic appearance. Functionally, the subcutaneous fat insulates the body, absorbs trauma, and serves as a reserve energy source.

Conditions of the human integumentary system constitute a broad spectrum of diseases, also known as dermatoses, as well as many nonpathologic states (like, in certain circumstances, melanonychia and racquet nails). While only a small number of skin diseases account for most visits to the physician, thousands of skin conditions have been described. Classification of these conditions often presents many nosological challenges, since underlying etiologies and pathogenetics are often not known. Therefore, most current textbooks present a classification based on location (for example, conditions of the mucous membrane), morphology (chronic blistering conditions), etiology (skin conditions resulting from physical factors), and so on. Clinically, the diagnosis of any particular skin condition is made by gathering pertinent information regarding the presenting skin lesion(s), including the location (such as arms, head, legs), symptoms (pruritus, pain), duration (acute or chronic), arrangement (solitary, generalized, annular, linear), morphology (macules, papules, vesicles), and color (red, blue, brown, black, white, yellow). Diagnosis of many conditions often also requires a skin biopsy which yields histologic information that can be correlated with the clinical presentation and any laboratory data.

Symptoms of an ingrown nail include pain along the margins of the nail (caused by hypergranulation that occurs around the aforementioned margins), worsening of pain when wearing tight footwear, and sensitivity to pressure of any kind, even the weight of bedsheets. Bumping of an affected toe can produce sharp and even excruciating pain as the tissue is punctured further by the nail. By the very nature of the condition, ingrown nails become easily infected unless special care is taken early to treat the condition by keeping the area clean. Signs of infection include redness and swelling of the area around the nail, drainage of pus and watery discharge tinged with blood. The main symptom is swelling at the base of the nail on the ingrowing side (though it may be both sides).

Onychocryptosis should not be confused with a similar nail disorder, convex nail, nor with other painful conditions such as involuted nails, nor with the presence of small corns, callus or debris down the nail sulci (grooves on either side).

Drug-induced nail changes are caused by drug administration which may result in a large number of nail abnormalities, usually with multiple nails being affected at the same time.

Neoplasms of the nailbed may often present with paronychia, ingrown nail, onycholysis, pyogenic granuloma, nail-plate dystrophy, longitudinal erythronychia, bleeding, and discolorations. There are various benign and malignant neoplasms that may occur in or overlying the nail matrix and in the nailbed, and symptoms may include pain, itching, and throbbing.

Benign tumors of the nails include verruca, pyogenic granuloma, fibromas, nevus cell nevi, myxoid cysts, angiofibromas (Koenen tumors), and epidermoid cysts.

Squamous cell carcinoma of the nailbed is uncommon, and often mistaken for a pyogenic granuloma initially. Subungual melanoma is frequently diagnosed late in the course of growth.

Symptoms include lack of sweat glands, thin hair, brittle nails, mottled skin, and lack of fingerprints.

Onychorrhexis (from the Greek words ὄνυχο- "ónycho-", "nail" and ῥῆξις "rhexis", "bursting"), also known as brittle nails, is a brittleness with breakage of finger or toenails that may result from excessive strong soap and water exposure, nail polish remover, hypothyroidism, anemia, anorexia nervosa or bulimia, or after oral retinoid therapy. Onychorrhexis affects up to 20% of the population.

An ingrown nail (also known as onychocryptosis from ὄνυξ ("onyx", "nail") + κρυπτός ("kryptos", "hidden") or unguis incarnates) is a common form of nail disease. It is an often painful condition in which the nail grows so that it cuts into one or both sides of the paronychium or nail bed.

The common opinion is that the nail enters inside the paronychium, but an ingrown toenail can simply be overgrown toe skin. The condition starts from a microbial inflammation of the paronychium, then a granuloma, which results in a nail buried inside of the granuloma. While ingrown nails can occur in the nails of both the hands and the feet , they occur most commonly with the toenails.

A true ingrown toenail is caused by the actual penetration of flesh by a sliver of nail.

SAPHO syndrome includes a variety of inflammatory bone disorders that may be associated with skin changes. These diseases share some clinical, radiologic, and pathologic characteristics.

An entity initially known as chronic recurrent multifocal osteomyelitis (CRMO) was first described in 1972. Subsequently, in 1978, several cases of CRMO were associated with blisters on the palms and soles (palmoplantar pustulosis). Since then, a number of associations between skin conditions and osteoarticular disorders have been reported under a variety of names, including sternocostoclavicular hyperostosis, pustulotic arthro-osteitis, and acne-associated spondyloarthropathy. The term SAPHO (synovitis, acne, pustulosis, hyperostosis, osteitis) was coined in 1987 to represent this spectrum of inflammatory bone disorders that may or may not be associated with dermatologic pathology.

The definition is Synovitis Acne (commonly involving the face and upper back) Pustulosis Hyperostosis Osteitis

DPR is comparable to Naegeli syndrome, both of which are caused by a specific defect in the keratin 14 protein.

Anonychia is the absence of nails, an anomaly, which may be the result of a congenital ectodermal defect, ichthyosis, severe infection, severe allergic contact dermatitis, self-inflicted trauma, Raynaud phenomenon, lichen planus, epidermolysis bullosa, or severe exfoliative diseases.

Common symptoms include:

- Excess keratin in nail beds and thickening of the nails

- Hyperkeratosis on hands and feet

- Oral lesions that look like thick white plaques

- Steatocystoma multiplex

- Pain

- Blisters