Identifying Primary and Secondary Skin Lesions

Primary skin lesions are present at the onset of a disease. In contrast, secondary skin lesions result from changes over time caused by disease progression, manipulation (scratching, picking, rubbing), or treatment. These 2 types of skin lesions can be differentiated as follows:

Primary lesions

* Bulla-a vesicle (see definition below) greater than 5 mm in diameter

* Cyst-an elevated, circumscribed area of the skin filled with liquid or semisolid fluid

* Macule-a flat, circumscribed area; can be brown, red, white, or tan

* Nodule-an elevated, firm, circumscribed, and palpable area greater than 5 mm in diameter; can involve all skin layers

* Papule-an elevated, palpable, firm, circumscribed area generally less than 5 mm in diameter

* Plaque-an elevated, flat-topped, firm, rough, superficial papule greater than 2 cm in diameter; papules can coalesce to form plaques

* Pustule-an elevated, superficial area that is similar to a vesicle but filled with pus

* Vesicle-an elevated, circumscribed, superficial, fluid-filled blister less than 5 mm in diameter

* Wheal-an elevated, irregularly shaped area of cutaneous edema; wheals are solid, transient, and changeable, with a variable diameter; can be red, pale pink, or white.

Secondary lesions

* Crust-a slightly elevated area of variable size; consists of dried serum, blood, or purulent exudate

* Excoriation-linear scratches that may or may not be denuded

* Lichenification-rough, thickened epidermis; accentuated skin markings caused by rubbing or scratching (eg, chronic eczema and lichen simplex)

* Scale-heaped-up keratinized cells; flakey exfoliation; irregular; thick or thin; dry or oily; variable size; can be white or tan.

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