« Back to General Dermatology FAQs

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 the difference between petechiae and purpura?

The size of the lesion is the major difference. Both petechiae and purpura result from extravasation of red blood cells into the dermis; hence, they do not blanch with pressure. Petechiae, however, are much smaller than purpura; they are ,5 mm in diameter.