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Morphology of Primary and Secondary Skin Lesions

»	Why do dermatologists use words that no one else understands?
»	But why are the descriptions so long?
»	How can I possibly learn the language of dermatology?
»	What is a primary skin lesion?
»	How is each of the primary lesions defined?
»	How do you determine whether a lesion is flat or raised?
»	How does a primary lesion differ from a secondary lesion?
»	How are secondary skin lesions defined?
»	What is a maculopapular eruption?
»	Give some examples of special skin lesions.
»	What are telangiectasias?
»	Are telangiectasias pathognomonic for a certain disease?
»	What is a burrow?
»	What is a comedo?
»	What is the difference between petechiae and purpura?
»	What are targetoid (target) lesions?
»	List some of the additional descriptive adjectives used in dermatology that refer to color or pigmentation.
»	How do atrophy and lichenification differ?
»	Do skin diseases have characteristic arrangements or configurations?
»	What is the Koebner phenomenon?
»	Do skin diseases characteristically occur in certain locations?

What is a comedo?

Fig. 2.3 Comedo.

A comedo (Fig. 2-3) is a folliculocentric collection of sebum and keratin. Comedonal acne characteristically consists of both open (blackheads) and closed comedones (whiteheads). When the contents of a closed comedo are exposed to air, a chemical reaction occurs, imparting the black color of an open comedo.