A skin lesion is a part of the skin that has an abnormal growth or appearance compared to the skin around it. There are two categories of skin lesions, primary and secondary. Primary skin lesions are present at birth or are acquired over your lifetime. A birthmark would be an example of a primary skin lesion. Secondary skin lesions evolve from primary lesions or develop as a consequence of your activities. Melanoma resulting from sun exposure would be an example of a secondary skin lesion.