How does a primary lesion differ from a secondary lesion?

Secondary skin lesions are created by scratching, scrubbing, or infection. They may also develop normally with time. For example, the primary lesion in a sunburn is a macular erythema (although it could also be a blister), but with  resolution, scale and increased pigmentation become prominent. Examples of secondary lesions include:
Crusts
Scale
Ulcers
Fissures
Excoriations
Scars
Erosions
Postinflammatory hyperpigmentation