Primary lesions include the following:
- Macules are up to 1 cm and are circumscribed, flat discolorations of the skin. Examples: freckles, flat nevi.
- Patches are larger than 1 cm and are circumscribed, flat discolorations of the skin. Examples: vitiligo, senile freckles, measles rash.
- Papules are up to 1 cm and are circumscribed, elevated, superficial, solid lesions. Examples: elevated nevi, warts, lichen planus. A wheal is a type of papule that is edematous and transitory (present less than 24 hours). Examples: Hives, sometimes insect bites.
- Plaques are larger than 1 cm and are circumscribed, elevated, superficial, solid lesions. Examples: mycosis fungoides, lichen simplex chronicus.
- Nodules range to 1 cm and are solid lesions with depth; they may be above, level with, or beneath the skin surface. Examples: nodular secondary or tertiary syphilis, basal cell cancers, xanthomas.
- Tumors are larger than 1 cm and are solid lesions with depth; they may be above, level with, or beneath the skin surface. Examples: tumor stage of mycosis fungoides, larger basal cell cancers.
- Vesicles range to 1 cm and are circumscribed elevations of the skin containing serous fluid. Examples: early chickenpox, zoster, contact dermatitis.
- Bullae are larger than 1 cm and are circumscribed elevations containing serous fluid. Examples: pemphigus, second-degree burns.
- Pustules vary in size and are circumscribed elevations of the skin containing purulent fluid. Examples: acne, impetigo.
- Petechiae range to 1 cm and are circumscribed deposits of blood or blood pigments. Examples: thrombocytopenia and drug eruptions.
- Purpura is a larger than 1 cm circumscribed deposit of blood or blood pigment in the skin. Examples: senile purpura and vasculitis.
Secondary lesions include the following:
- Scales are shedding, dead epidermal cells that may be dry or greasy. Examples: dandruff (greasy), psoriasis (dry).
- Crusts are variously colored masses of skin exudates. Examples: impetigo, infected dermatitis.
- Excoriations are abrasions of the skin, usually superficial and traumatic. Examples: scratched insect bites, scabies.
- Fissures are linear breaks in the skin, sharply defined with abrupt walls. Examples: congenital syphilis, athlete’s foot.
- Ulcers are irregularly sized and shaped excavations in the skin extending into the dermis or deeper. Examples: stasis ulcers of legs, tertiary syphilis.
- Scars are formations of connective tissue replacing tissue lost through injury or disease.
- Keloids are hypertrophic scars beyond the borders of the original injury.
- Lichenification is a diffuse area of thickening and scaling with resultant increase in the skin lines and markings.
Several combinations of primary and secondary lesions commonly exist on the same patient. Examples: papulosquamous lesions of psoriasis, vesiculopustular lesions in contact dermatitis, and crusted excoriations in scabies.
Some primary lesions, limited to a few skin diseases, can be called specialized lesions.
- Comedones or blackheads are plugs of whitish or blackish sebaceous and keratinous material lodged in the pilosebaceous follicle, usually seen on the face, the chest, or the back, rarely on the upper part of the arms. Example: acne.
- Milia are whitish nodules, 1 to 2 mm in diameter, that have no visible opening onto the skin surface. Examples: in healed burn or superficial traumatic sites, healed bullous disease sites, or newborns.
- Telangiectasias are dilated superficial blood vessels. Examples: spider hemangiomas, chronic radiodermatitis.
- Burrows are very small and short (in scabies) or tortuous and long (in creeping eruption) tunnels in the epidermis.
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