Primary Dermatological Lesions
Primary lesions are physical changes in the skin considered to be caused directly by the disease process.
Types of primary lesions are rarely specific to a single disease entity.

A. BURROW: burrows are linear/curvilinear lesions produced by infestation of the skin and formation of tunnels (namely by the scabitic mite or by cutaneous larva migrans).

B. COMEDONE: a plug of keratin and sebum wedged in a dilated pilosebaceous orifice 

C. MACULE: a circumscribed flat area of altered colour e.g. freckle. A macule greater than 1 cm. may be referred to as a patch.

D. PAPILLOMA: a projecting nipple-like mass e.g. skin tag 

E. PAPULE: a discrete elevation of skin that may be changed in colour. Those arising from the subcutis may be felt rather than seen. Larger lesions (>1 cm) are referred to as nodules. Papules may have a variety of shapes in profile (domed, flat-topped, umbilicated) and may be associated with secondary features such as crusts or scales.

F. PETECHIAE and PURPURA: Petechiae are pinhead-sized flat macules of extravascular blood in the dermis.

                                                          Purpura are larger and may be palpable

                                                          Ecchymosis ('bruise') is where bleeding involves deeper structures 

G. PLAQUE: solid, raised, flat-topped area of skin greater than 1cm in diameter. It is analogous to the geological formation, the plateau. e.g. psoriasis plaque

H. PUSTULE: circumscribed elevated lesions that contain pus. They are most commonly infected (as in folliculitis) but may be sterile (as in pustular psoriasis)

I. SCALE: flake-like compacted desquamated layers of stratum corneum. Desquamation occurs when there are peeling sheets of scale following acute injury to the skin. e.g. psoriasis


J. TELANGIECTASIA: visible (and permanent) dilatation of small cutaneous blood vessels in the skin. Can be isolated lesions or part of a generalized disorder, such as ataxia telangiectasia.


K. VESICLE and BULLA:  small (few mm) and larger (several cm) fluid-filled blisters respectively. Filled with clear fluid. e.g. pemphigoid


L. WEAL: an area of dermal oedema, usually white due to masking of local blood supply by fluid, e.g. nettle sting


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