Introduction to Skin Lesions (3 of 6)

Definitions of Primary and Secondary Lesions

Primary skin lesions are those which develop as a direct result of the disease process.  Secondary lesions are those which evolve from primary lesions or develop as a consequence of the patient's activities.

This classification is naturally artificial; the same lesion type might be a primary lesion in one disease but a secondary lesion in another (eg alopecia is a primary lesion in canine hypothyroidism [direct consequence of lack of thyroxine] but a secondary lesion in feline flea allergy [caused by the patient: hair removed by the itchy cat]).

Do not confuse the term "secondary lesion" with "secondary pyoderma".  The latter term implies a bacterial infection which is complicating an underlying skin disease (common examples in dogs include allergy or demodicosis) but that secondary pyoderma may present with primary lesions such as papules and pustules.