An extensive language has been developed to standardize the description of skin lesions, including
Lesion configuration Lesion Configuration (Secondary Morphology) An extensive language has been developed to standardize the description of skin lesions, including Lesion type (sometimes called primary morphology) Lesion configuration (sometimes called secondary... read more (sometimes called secondary morphology)
Rash is a general term for a temporary skin eruption.
(See also Evaluation of the Dermatologic Patient Evaluation of the Dermatologic Patient History and physical examination are adequate for diagnosing many skin lesions. Some require biopsy or other testing. Important information to obtain from history includes Personal or family... read more and Diagnostic Tests for Skin Disorders Diagnostic Tests for Skin Disorders Diagnostic tests are indicated when the cause of a skin lesion or disease is not obvious from history and physical examination alone. These include Patch testing Biopsy Scrapings Examination... read more .)
Cross-section of the skin and skin structures
Lesion Type (Primary Morphology)
Macules are flat, nonpalpable lesions usually < 10 mm in diameter. Macules represent a change in color and are not raised or depressed compared to the skin surface. A patch is a large macule. Examples include freckles, flat moles, tattoos, and port-wine stains Capillary Malformations Capillary malformations are present at birth and appear as flat, pink, red, or purplish lesions. Port-wine stains are capillary vascular malformations that are present at birth and that manifest... read more , and the rashes of rickettsial infections Overview of Rickettsial and Related Infections Rickettsial diseases (rickettsioses) and related diseases (anaplasmosis, ehrlichiosis, Q fever, scrub typhus) are caused by a group of gram-negative, obligately intracellular coccobacilli. All... read more , rubella Rubella (See also Congenital Rubella.) Rubella is a contagious viral infection that may cause adenopathy, rash, and sometimes constitutional symptoms, which are usually mild and brief. Infection during... read more , measles Measles Measles is a highly contagious viral infection that is most common among children. It is characterized by fever, cough, coryza, conjunctivitis, an enanthem (Koplik spots) on the oral mucosa... read more (can also have papules and plaques), and some allergic drug eruptions Drug Eruptions and Reactions Drugs can cause multiple skin eruptions and reactions. The most serious of these are discussed elsewhere in THE MANUAL and include Stevens-Johnson syndrome and toxic epidermal necrolysis, hypersensitivity... read more .
Papules are elevated lesions usually < 10 mm in diameter that can be felt or palpated. Examples include nevi, warts, lichen planus Lichen Planus Lichen planus is a recurrent, pruritic, inflammatory eruption characterized by small, discrete, polygonal, flat-topped, violaceous papules that may coalesce into rough scaly plaques, often accompanied... read more , insect bites, seborrheic keratoses Seborrheic Keratoses Seborrheic keratoses are superficial, often pigmented, epithelial lesions that are usually warty but may occur as smooth papules. The cause of seborrheic keratosis is unknown, but genetic mutations... read more , actinic keratoses Actinic keratoses Chronic affects of sunlight include photoaging, actinic keratoses, and skin cancer. (See also Overview of Effects of Sunlight.) Chronic exposure to sunlight ages the skin (photoaging, dermatoheliosis... read more , some lesions of acne Acne Vulgaris Acne vulgaris is the formation of comedones, papules, pustules, nodules, and/or cysts as a result of obstruction and inflammation of pilosebaceous units (hair follicles and their accompanying... read more , and skin cancers Overview of Skin Cancer Skin cancer is the most common type of cancer and commonly develops in sun-exposed areas of skin. The incidence is highest among outdoor workers, sportsmen, and sunbathers and is inversely related... read more . The term maculopapular is often loosely and improperly used to describe many red rashes; because this term is nonspecific and easily misused, it should be avoided.
Plaques are palpable lesions > 10 mm in diameter that are elevated or depressed compared to the skin surface. Plaques may be flat topped or rounded. Lesions of psoriasis Psoriasis Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including... read more and granuloma annulare Granuloma Annulare Granuloma annulare is a benign, chronic, idiopathic condition characterized by papules or nodules that spread peripherally to form a ring around normal or slightly depressed skin. Diagnosis... read more commonly form plaques.
Nodules are firm papules or lesions that extend into the dermis or subcutaneous tissue. Examples include cysts Cutaneous Cysts Epidermal inclusion cysts are the most common cutaneous cysts. Milia are small epidermal inclusion cysts. Pilar cysts are usually on the scalp and may be familial. Benign cutaneous cysts are... read more , lipomas Lipomas Lipomas are soft, movable, subcutaneous nodules of adipocytes (fat cells); overlying skin appears normal. This photo shows a lipoma on the extremity. Lipomas are very common, benign, and usually... read more , and fibromas Dermatofibromas Dermatofibromas are firm, red-to-brown, small papules or nodules composed of fibroblastic tissue. They usually occur on the thighs or legs but can occur anywhere. This photo shows a small hyperpigmented... read more .
Vesicles are small, clear, fluid-filled blisters < 10 mm in diameter. Vesicles are characteristic of herpes infections, acute allergic contact dermatitis Allergic contact dermatitis (ACD) Contact dermatitis is inflammation of the skin caused by direct contact with irritants (irritant contact dermatitis) or allergens (allergic contact dermatitis). Symptoms include pruritus and... read more , and some autoimmune blistering disorders (eg, dermatitis herpetiformis Dermatitis Herpetiformis Dermatitis herpetiformis is an intensely pruritic, chronic, autoimmune, papulovesicular cutaneous eruption strongly associated with celiac disease. Typical findings are clusters of intensely... read more ).
Bullae are clear fluid-filled blisters > 10 mm in diameter. These may be caused by burns, bites, irritant contact dermatitis Irritant contact dermatitis (ICD) Contact dermatitis is inflammation of the skin caused by direct contact with irritants (irritant contact dermatitis) or allergens (allergic contact dermatitis). Symptoms include pruritus and... read more or allergic contact dermatitis Allergic contact dermatitis (ACD) Contact dermatitis is inflammation of the skin caused by direct contact with irritants (irritant contact dermatitis) or allergens (allergic contact dermatitis). Symptoms include pruritus and... read more , and drug reactions. Classic autoimmune bullous diseases include pemphigus vulgaris Pemphigus Vulgaris Pemphigus vulgaris is an uncommon, potentially fatal, autoimmune disorder characterized by intraepidermal blisters and extensive erosions on apparently healthy skin and mucous membranes. Diagnosis... read more and bullous pemphigoid Bullous Pemphigoid Bullous pemphigoid is a chronic autoimmune skin disorder resulting in generalized, pruritic, bullous lesions in older patients. Mucous membrane involvement is rare. Diagnosis is by skin biopsy... read more . Bullae also may occur in inherited disorders of skin fragility.
Pustules are vesicles that contain pus. Pustules are common in bacterial infections and folliculitis and may arise in some inflammatory disorders including pustular psoriasis Subtypes of Psoriasis Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including... read more .
Urticaria Urticaria Urticaria consists of migratory, well-circumscribed, erythematous, pruritic plaques on the skin. Urticaria also may be accompanied by angioedema, which results from mast cell and basophil activation... read more (wheals or hives) is characterized by elevated lesions caused by localized edema. Wheals are pruritic and red. Wheals are a common manifestation of hypersensitivity to drugs, stings or bites, autoimmunity, and, less commonly, physical stimuli including temperature, pressure, and sunlight. The typical wheal lasts < 24 hours.
Scale is heaped-up accumulations of horny epithelium that occur in disorders such as psoriasis Psoriasis Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including... read more , seborrheic dermatitis Seborrheic Dermatitis Seborrheic dermatitis is a common inflammatory condition of skin regions with a high density of sebaceous glands (eg, face, scalp, sternum). The cause is unknown, but species of Malassezia,... read more , and fungal infections. Pityriasis rosea Pityriasis Rosea Pityriasis rosea is a self-limited, inflammatory disease characterized by diffuse, scaling papules or plaques. Treatment is usually unnecessary. Pityriasis rosea most commonly occurs between... read more and chronic dermatitis of any type may be scaly.
Crusts (scabs) consist of dried serum, blood, or pus. Crusting can occur in inflammatory or infectious skin diseases (eg, impetigo Impetigo and Ecthyma Impetigo is a superficial skin infection with crusting or bullae caused by streptococci, staphylococci, or both. Ecthyma is an ulcerative form of impetigo. Diagnosis is clinical. Treatment is... read more ).
Erosions are open areas of skin that result from loss of part or all of the epidermis. Erosions can be traumatic or can occur with various inflammatory or infectious skin diseases. An excoriation is a linear erosion caused by scratching, rubbing, or picking.
Ulcers result from loss of the epidermis and at least part of the dermis. Causes include venous stasis dermatitis Stasis Dermatitis Stasis dermatitis is inflammation, typically of the skin of the lower legs, caused by chronic edema. Symptoms are itching, scaling, and hyperpigmentation. Ulceration can be a complication. Diagnosis... read more , physical trauma with or without vascular compromise (eg, caused by decubitus ulcers Pressure Injuries Pressure injuries are areas of necrosis and often ulceration (also called pressure ulcers) where soft tissues are compressed between bony prominences and external hard surfaces. They are caused... read more or peripheral arterial disease Peripheral Arterial Disease Peripheral arterial disease (PAD) is atherosclerosis of the extremities (virtually always lower) causing ischemia. Mild PAD may be asymptomatic or cause intermittent claudication; severe PAD... read more ), infections, and vasculitis Cutaneous Vasculitis Cutaneous vasculitis refers to vasculitis affecting small- or medium-sized vessels in the skin and subcutaneous tissue but not the internal organs. Cutaneous vasculitis may be limited to the... read more .
Petechiae are nonblanchable punctate foci of hemorrhage. Causes include platelet abnormalities (eg, thrombocytopenia, platelet dysfunction Overview of Platelet Disorders Platelets are cell fragments that function in the clotting system. Thrombopoietin helps control the number of circulating platelets by stimulating the bone marrow to produce megakaryocytes,... read more ), vasculitis Overview of Vasculitis Vasculitis is inflammation of blood vessels, often with ischemia, necrosis, and organ inflammation. Vasculitis can affect any blood vessel—arteries, arterioles, veins, venules, or capillaries... read more , and infections (eg, meningococcemia, Rocky Mountain spotted fever Rocky Mountain Spotted Fever (RMSF) Rocky Mountain spotted fever (RMSF) is caused by Rickettsia rickettsii and transmitted by ixodid ticks. Symptoms are high fever, severe headache, and rash. (See also Overview of Rickettsial... read more , other rickettsioses).
Purpura is a larger area of hemorrhage that may be palpable. Palpable purpura is considered the hallmark of leukocytoclastic vasculitis. Purpura may indicate a coagulopathy. Large areas of purpura may be called ecchymoses or, colloquially, bruises.
Atrophy is thinning of the skin, which may appear dry and wrinkled, resembling cigarette paper. Atrophy may be caused by chronic sun exposure, aging, and some inflammatory and neoplastic skin diseases, including cutaneous T-cell lymphoma Cutaneous T-cell Lymphomas (CTCL) Mycosis fungoides and Sézary syndrome are uncommon chronic T-cell lymphomas primarily affecting the skin and occasionally the lymph nodes. (See also Overview of Lymphoma.) Mycosis fungoides... read more and lupus erythematosus Variant Forms of Lupus Systemic lupus erythematosus is a chronic, multisystem, inflammatory disorder of autoimmune etiology, occurring predominantly in young women. Common manifestations may include arthralgias and... read more . Atrophy also may result from long-term use of potent topical corticosteroids.
Scars are areas of fibrosis that replace normal skin after injury. Some scars become hypertrophic or thickened and raised. Keloids Keloids Keloids are smooth overgrowths of fibroblastic tissue that arise in an area of injury (eg, lacerations, surgical scars, truncal acne) or, occasionally, spontaneously. Keloids are more frequent... read more are hypertrophic scars that extend beyond the original wound margin.
Telangiectases are foci of small, permanently dilated blood vessels that may occur in areas of sun damage, rosacea Rosacea Rosacea is a chronic inflammatory disorder characterized by facial flushing, telangiectasias, erythema, papules, pustules, and, in severe cases, rhinophyma. Diagnosis is based on the characteristic... read more , systemic diseases (especially systemic sclerosis Systemic Sclerosis Systemic sclerosis is a rare chronic disease of unknown cause characterized by diffuse fibrosis and vascular abnormalities in the skin, joints, and internal organs (especially the esophagus... read more ), or inherited diseases (eg, ataxia-telangiectasia Ataxia-Telangiectasia Ataxia-telangiectasia results from a DNA repair defect that frequently results in humoral and cellular deficiency; it causes progressive cerebellar ataxia, oculocutaneous telangiectasias, and... read more , hereditary hemorrhagic telangiectasia Hereditary Hemorrhagic Telangiectasia Hereditary hemorrhagic telangiectasia is a hereditary disorder of vascular malformation transmitted as an autosomal dominant trait affecting men and women. (See also Overview of Vascular Bleeding... read more ) or after long-term therapy with topical fluorinated corticosteroids.
Lesion Configuration (Secondary Morphology)
Configuration is the shape of single lesions and the arrangement of clusters of lesions.
Linear lesions take on the shape of a straight line and are suggestive of some forms of contact dermatitis Contact Dermatitis Contact dermatitis is inflammation of the skin caused by direct contact with irritants (irritant contact dermatitis) or allergens (allergic contact dermatitis). Symptoms include pruritus and... read more , linear epidermal nevi, and lichen striatus. Excoriations resulting from scratching are typically linear.
Annular lesions are rings with central clearing. Examples include granuloma annulare Granuloma Annulare Granuloma annulare is a benign, chronic, idiopathic condition characterized by papules or nodules that spread peripherally to form a ring around normal or slightly depressed skin. Diagnosis... read more , some drug eruptions, some dermatophyte infections Overview of Dermatophytoses Dermatophytoses are fungal infections of keratin in the skin and nails (nail infection is called tinea unguium or onychomycosis). Symptoms and signs vary by site of infection. Diagnosis is by... read more (eg, tinea [ringworm]), and secondary syphilis Secondary syphilis Syphilis is caused by the spirochete Treponema pallidum and is characterized by 3 sequential clinical, symptomatic stages separated by periods of asymptomatic latent infection. Common manifestations... read more .
Nummular lesions are circular or coin-shaped; an example is nummular eczema Nummular Dermatitis Nummular dermatitis is inflammation of the skin characterized by coin-shaped or discoid eczematous lesions. Diagnosis is clinical. Treatment may include topical corticosteroids and phototherapy... read more .
Target (bull’s-eye or iris) lesions appear as rings with central duskiness and are classic for erythema multiforme Erythema Multiforme Erythema multiforme is an inflammatory reaction, characterized by target or iris skin lesions. Oral mucosa may be involved. Diagnosis is clinical. Lesions spontaneously resolve but frequently... read more .
Serpiginous lesions have linear, branched, and curving elements. Examples include some fungal and parasitic infections (eg, cutaneous larva migrans Cutaneous Larva Migrans Cutaneous larva migrans is the skin manifestation of hookworm infestation. Cutaneous larva migrans is caused by Ancylostoma species, most commonly dog or cat hookworm Ancylostoma braziliense... read more ).
Reticulated lesions have a lacy or networked pattern. Examples include cutis marmorata and livedo reticularis.
Herpetiform describes grouped papules or vesicles arranged like those of a herpes simplex infection Herpes Simplex Virus (HSV) Infections Herpes simplex viruses (human herpesviruses types 1 and 2) commonly cause recurrent infection affecting the skin, mouth, lips, eyes, and genitals. Common severe infections include encephalitis... read more .
Zosteriform describes lesions clustered in a dermatomal distribution similar to those of herpes zoster Herpes Zoster Herpes zoster is infection that results when varicella-zoster virus reactivates from its latent state in a posterior dorsal root ganglion. Symptoms usually begin with pain along the affected... read more .
Texture of Skin Lesions
Some skin lesions have visible or palpable texture that suggests a diagnosis.
Verrucous lesions have an irregular, pebbly, or rough surface. Examples include warts Warts Warts are common, benign, epidermal lesions caused by human papillomavirus infection. They can appear anywhere on the body in a variety of morphologies. Diagnosis is by examination. Warts are... read more and seborrheic keratoses Seborrheic Keratoses Seborrheic keratoses are superficial, often pigmented, epithelial lesions that are usually warty but may occur as smooth papules. The cause of seborrheic keratosis is unknown, but genetic mutations... read more .
Lichenification is thickening of the skin with accentuation of normal skin markings; it results from repeated scratching or rubbing.
Induration, or deep thickening of the skin, can result from edema, inflammation, or infiltration, including by cancer. Indurated skin has a hard, resistant feeling. Induration is characteristic of panniculitis Panniculitis Panniculitis describes inflammation of the subcutaneous fat that can result from multiple causes. Diagnosis is by clinical evaluation and biopsy. Treatment depends on the cause. (See also Erythema... read more , some skin infections, and cutaneous metastatic cancers.
Umbilicated lesions have a central indentation and are usually viral. Examples include molluscum contagiosum Molluscum Contagiosum Molluscum contagiosum is characterized by clusters of pink, dome-shaped, smooth, waxy, or pearly and umbilicated papules 2 to 5 mm in diameter caused by molluscum contagiosum virus, a poxvirus... read more and herpes simplex Herpes Simplex Virus (HSV) Infections Herpes simplex viruses (human herpesviruses types 1 and 2) commonly cause recurrent infection affecting the skin, mouth, lips, eyes, and genitals. Common severe infections include encephalitis... read more .
Xanthomas, which are yellowish, waxy lesions, may be idiopathic or may occur in patients who have lipid disorders.
Location and Distribution of Skin Lesions
It is important to note whether
Lesions are single or multiple.
Particular body parts are affected (eg, palms or soles, scalp, mucosal membranes).
Distribution is random or patterned, symmetric or asymmetric.
Lesions are on sun-exposed or protected skin.
Although few patterns are pathognomonic, some are consistent with certain diseases.
Psoriasis Psoriasis Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including... read more frequently affects the scalp, extensor surfaces of the elbows and knees, umbilicus, and the gluteal cleft.
Lichen planus Lichen Planus Lichen planus is a recurrent, pruritic, inflammatory eruption characterized by small, discrete, polygonal, flat-topped, violaceous papules that may coalesce into rough scaly plaques, often accompanied... read more frequently arises on the wrists, forearms, genitals, and lower legs.
Vitiligo Vitiligo Vitiligo is a loss of skin melanocytes that causes areas of skin depigmentation of varying sizes. Cause is unknown, but genetic and autoimmune factors are likely. Diagnosis is usually clear... read more may be patchy and isolated or may group around the distal extremities and face, particularly around the eyes and mouth.
Discoid lupus erythematosus Variant Forms of Lupus Systemic lupus erythematosus is a chronic, multisystem, inflammatory disorder of autoimmune etiology, occurring predominantly in young women. Common manifestations may include arthralgias and... read more has characteristic lesions on sun-exposed skin of the face, especially the forehead, nose, and the conchal bowl of the ear.
Hidradenitis suppurativa Hidradenitis Suppurativa Hidradenitis suppurativa is a chronic, scarring, acnelike inflammatory process that occurs in the axillae, groin, and around the nipples and anus. Diagnosis is by examination. Treatment depends... read more involves skin containing a high density of apocrine glands, including the axillae, groin, and under the breasts.
When examining the color of skin, health care practitioners should note that the natural color of a patient's skin can change the appearance of colors.
Red skin (erythema) can result from many different inflammatory or infectious diseases. Cutaneous tumors are often pink or red. Superficial vascular lesions such as port-wine stains may appear red.
Orange skin is most often seen in hypercarotenemia, a usually benign condition of carotene deposition after excess dietary ingestion of beta-carotene.
Yellow skin is typical of jaundice Jaundice Jaundice is a yellowish discoloration of the skin and mucous membranes caused by hyperbilirubinemia. Jaundice becomes visible when the bilirubin level is about 2 to 3 mg/dL (34 to 51 micromol/L)... read more , xanthelasmas Xanthelasma The skin of the eyelids is a common site for benign and malignant growths. A xanthelasma is a slightly raised, yellow-white, well-circumscribed plaque that typically appears along the nasal... read more and xanthomas, and pseudoxanthoma elasticum Pseudoxanthoma Elasticum Pseudoxanthoma elasticum is a rare genetic disorder characterized by calcification of the elastic fibers of the skin, retina, and cardiovascular system. Diagnosis is clinical. There is no specific... read more .
Green fingernails Discoloration Deformities are often considered together with dystrophies, but the two are slightly different; deformities are generally considered to be gross changes in nail shape, whereas dystrophies are... read more suggest Pseudomonas aeruginosa infection.
Violet skin may result from cutaneous hemorrhage or vasculitis Overview of Vasculitis Vasculitis is inflammation of blood vessels, often with ischemia, necrosis, and organ inflammation. Vasculitis can affect any blood vessel—arteries, arterioles, veins, venules, or capillaries... read more . Vascular lesions or tumors, such as Kaposi sarcoma Kaposi Sarcoma Kaposi sarcoma is a multicentric vascular tumor caused by herpesvirus type 8. It can occur in classic, AIDS-associated, endemic (in Africa), and iatrogenic (eg, after organ transplantation)... read more and hemangiomas, can appear purple. A lilac color of the eyelids or heliotrope eruption is characteristic of dermatomyositis Autoimmune Myositis Autoimmune myositis is characterized by inflammatory and degenerative changes in the muscles (polymyositis) or in the skin and muscles (dermatomyositis). Manifestations include symmetric weakness... read more .
Shades of blue, silver, and gray can result from deposition of drugs or metals in the skin, including minocycline, amiodarone, and silver (argyria). Ischemic skin appears purple to gray in color. Deep dermal nevi appear blue.
Black skin lesions may be melanocytic, including nevi and melanoma Melanoma Malignant melanoma arises from melanocytes in a pigmented area (eg, skin, mucous membranes, eyes, or central nervous system). Metastasis is correlated with depth of dermal invasion. With spread... read more . Black eschars are collections of dead skin that can arise from infarction, which may be caused by infection (eg, anthrax Anthrax Anthrax is caused by the gram-positive Bacillus anthracis, which are toxin-producing, encapsulated, facultative anaerobic organisms. Anthrax, an often fatal disease of animals, is transmitted... read more , angioinvasive fungi including Rhizopus, meningococcemia Meningococcal Diseases Meningococci (Neisseria meningitidis) are gram-negative cocci that cause meningitis and meningococcemia. Symptoms, usually severe, include headache, nausea, vomiting, photophobia, lethargy,... read more ), calciphylaxis Calciphylaxis All patients undergoing long-term renal replacement therapy (RRT) develop accompanying metabolic and other disorders. These disorders require appropriate attention and adjunctive treatment.... read more , arterial insufficiency, or vasculitis Cutaneous Vasculitis Cutaneous vasculitis refers to vasculitis affecting small- or medium-sized vessels in the skin and subcutaneous tissue but not the internal organs. Cutaneous vasculitis may be limited to the... read more .
Other Clinical Signs of Skin Lesions
Dermatographism (dermographism) is the appearance of an urticarial wheal after focal pressure (eg, stroking or scratching the skin) in the distribution of the pressure. Up to 5% of normal patients may exhibit this sign, which is a form of physical urticaria.
Darier sign refers to rapid swelling of a lesion when stroked. It occurs in patients with urticaria pigmentosa or mastocytosis Mastocytosis Mastocytosis is mast cell infiltration of skin or other tissues and organs. Symptoms result mainly from mediator release and include pruritus, flushing, and dyspepsia due to gastric hypersecretion... read more .
Nikolsky sign is epidermal shearing that occurs with gentle lateral pressure on seemingly uninvolved skin in patients with toxic epidermal necrolysis Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN) Stevens-Johnson syndrome and toxic epidermal necrolysis are severe cutaneous hypersensitivity reactions. Drugs, especially sulfa drugs, antiseizure drugs, and antibiotics, are the most common... read more and some autoimmune bullous diseases Introduction to Bullous Diseases Bullae are elevated, fluid-filled blisters ≥ 10 mm in diameter. The autoimmune bullous diseases include Bullous pemphigoid Dermatitis herpetiformis Epidermolysis bullosa read more .
Auspitz sign is the appearance of pinpoint bleeding after scale is removed from plaques in psoriasis Psoriasis Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including... read more .
Koebner phenomenon describes the development of lesions within areas of trauma (eg, caused by scratching, rubbing, or injury). Psoriasis frequently exhibits this phenomenon, as may lichen planus Lichen Planus Lichen planus is a recurrent, pruritic, inflammatory eruption characterized by small, discrete, polygonal, flat-topped, violaceous papules that may coalesce into rough scaly plaques, often accompanied... read more , often resulting in linear lesions.