List of skin conditions

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 metres, 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 interdigitates 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.
Acneiform eruptions.
Acneiform eruptions are caused by changes in the pilosebaceous unit.
Autoinflammatory syndromes.
Autoinflammatory syndromes are a group of inherited disorders characterized by bouts of inflammatory skin lesions and periodic fevers.
Chronic blistering.
Chronic blistering cutaneous conditions have a prolonged course and present with vesicles and bullae.
Conditions of the mucous membranes.
Conditions of the mucous membranes involve the moist linings of the eyes, nose, mouth, genitals, and anus.
Conditions of the skin appendages.
Conditions of the skin appendages are those affecting the glands of the skin, hair, nails, and arrector pili muscles.
Conditions of the subcutaneous fat.
Conditions of the subcutaneous fat are those affecting the layer of adipose tissue that lies between the dermis and underlying fascia.
Congenital anomalies.
Cutaneous congenital anomalies are a diverse group of disorders that result from faulty morphogenesis, the biological process that forms the shape of a human body.
Connective tissue diseases.
Connective tissue diseases are caused by a complex array of autoimmune responses that target or affect collagen or ground substance.
Abnormalities of dermal fibrous and elastic tissue.
Abnormalities of dermal fibrous and elastic tissue are caused by problems in the regulation of collagen synthesis or degradation.
Dermal and subcutaneous growths.
Dermal and subcutaneous growths result from (1) reactive or neoplastic proliferation of cellular components of the dermis or subcutaneous tissue, or (2) neoplasms invading or aberrantly present in the dermis.
Dermatitis.
Dermatitis is a general term for "inflammation of the skin".
Atopic.
Atopic dermatitis is a chronic dermatitis associated with a hereditary tendency to develop allergies to food and inhalant substances.
Contact.
Contact dermatitis is caused by certain substances coming in contact with the skin.
Eczema.
Eczema refers to a broad range of conditions that begin as spongiotic dermatitis and may progress to a lichenified stage.
Pustular.
Pustular dermatitis is an inflammation of the skin that presents with pustular lesions.
Seborrheic.
Seborrheic dermatitis is a chronic, superficial, inflammatory disease characterized by scaling on an erythematous base.
Disturbances of pigmentation.
Disturbances of human pigmentation, either loss or reduction, may be related to loss of melanocytes or the inability of melanocytes to produce melanin or transport melanosomes correctly.
Drug eruptions.
Drug eruptions are adverse drug reactions that present with cutaneous manifestations.
Endocrine-related.
Endocrine conditions often present with cutaneous findings as the skin interacts with the endocrine system in many ways.
Eosinophilic.
Eosinophilic cutaneous conditions encompass a wide variety of diseases that are characterized histologically by the presence of eosinophils in the inflammatory infiltrate, or evidence of eosinophil degranulation.
Epidermal nevi, neoplasms, and cysts.
Epidermal nevi, neoplasms, and cysts are skin lesions that develop from the epidermal layer of the skin.
Erythemas.
Erythemas are reactive skin conditions in which there is blanchable redness.
Genodermatoses.
Genodermatoses are inherited genetic skin conditions often grouped into three categories: chromosomal, single gene, and polygenetic.
Infection-related.
Infection-related cutaneous conditions may be caused by bacteria, fungi, yeast, viruses, or parasites.
Bacterium-related.
Bacterium-related cutaneous conditions often have distinct morphologic characteristics that may be an indication of a generalized systemic process or simply an isolated superficial infection.
"Mycobacterium"-related.
"Mycobacterium"-related cutaneous conditions are caused by "Mycobacterium" infections.
Mycosis-related.
Mycosis-related cutaneous conditions are caused by fungi or yeasts, and may present as either a superficial or deep infection of the skin, hair, or nails.
Parasitic infestations, stings, and bites.
Parasitic infestations, stings, and bites in humans are caused by several groups of organisms belonging to the following phyla: Annelida, Arthropoda, Bryozoa, Chordata, Cnidaria, Cyanobacteria, Echinodermata, Nemathelminthes, Platyhelminthes, and Protozoa.
Virus-related.
Virus-related cutaneous conditions are caused by two main groups of viruses–DNA and RNA types–both of which are obligatory intracellular parasites.
Lichenoid eruptions.
Lichenoid eruptions are dermatoses related to the unique, common inflammatory disorder lichen planus, which affects the skin, mucous membranes, nails, and hair.
Lymphoid-related.
Lymphoid-related cutaneous conditions are a group of disorders characterized by collections of lymphocyte cells within the skin.
Melanocytic nevi and neoplasms.
Melanocytic nevi and neoplasms are caused by either a proliferation of (1) melanocytes, or (2) nevus cells, a form of melanocyte that lack dendritic processes.
Melanoma.
Melanoma is a malignant proliferation of melanocytes and the most aggressive type of skin cancer.
Monocyte- and macrophage-related.
Monocyte- and macrophage-related cutaneous conditions are characterized histologically by infiltration of the skin by monocyte or macrophage cells, often divided into several categories, including granulomatous disease, histiocytoses, and sarcoidosis.
Mucinoses.
Mucinoses are a group of conditions caused by dermal fibroblasts producing abnormally large amounts of mucopolysaccharides.
Neurocutaneous.
Neurocutaneous conditions are due organic nervous system disease or are psychiatric in etiology.
Noninfectious immunodeficiency-related.
Noninfectious immunodeficiency-related cutaneous conditions are caused by T-cell or B-cell dysfunction.
Nutrition-related.
Nutrition-related cutaneous conditions are caused by malnutrition due to an improper or inadequate diet.
Papulosquamous hyperkeratotic.
Papulosquamous hyperkeratotic cutaneous conditions are those that present with papules and scales caused by a thickening of the stratum corneum.
Palmoplantar keratodermas.
Palmoplantar keratodermas are a diverse group of hereditary and acquired keratodermas in which there is hyperkeratosis of the skin of the palms and soles.
Pregnancy-related.
Pregnancy-related cutaneous conditions are a group of skin changes observed during pregnancy.
Pruritic.
Pruritus, commonly known as itchiness, is a sensation exclusive to the skin, and characteristic of many skin conditions.
Psoriasis.
Psoriasis is a common, chronic, and recurrent inflammatory disease of the skin characterized by circumscribed, erythematous, dry, scaling plaques.
Reactive neutrophilic.
Reactive neutrophilic cutaneous conditions constitute a spectrum of disease mediated by neutrophils, and typically associated with underlying diseases, such as inflammatory bowel disease and hematologic malignancy.
Recalcitrant palmoplantar eruptions.
Recalcitrant palmoplantar eruptions are skin conditions of the palms and soles which are resistant to treatment.
Resulting from errors in metabolism.
Skin conditions resulting from errors in metabolism are caused by enzymatic defects that lead to an accumulation or deficiency of various cellular components, including, but not limited to, amino acids, carbohydrates, and lipids.
Resulting from physical factors.
Skin conditions resulting from physical factors occur from a number of causes, including, but not limited to, hot and cold temperatures, friction, and moisture.
Ionizing radiation-induced.
Ionizing radiation-induced cutaneous conditions result from exposure to ionizing radiation.
Urticaria and angioedema.
Urticaria is a vascular reaction of the skin characterized by the appearance of wheals, which are firm, elevated swelling of the skin. Angioedema, which can occur alone or with
urticaria, is characterized by a well-defined, edematous swelling that involves subcutaneous tissues, abdominal organs, or upper airway.
Vascular-related.
Vascular-related cutaneous conditions result from dysfunction of the blood or blood vessels in the dermis, or lymphatics in the subcutaneous tissues.