Hawthorne states that the birthmark symbolises mortality to Aylmer. People are mortal and imperfect, just like everything else in nature. Aylmer wants to remove the birthmark based on his desire to make her perfect, to cure her of her sins and flaws.
Georgiana's birthmark horrifies Aylmer as he increasingly views it as a reminder of death. Aylmer decides to use his science to combat nature, to remove the mark that symbolises death, and take hold of power over life and death. With growing distaste for the birthmark, Aylmer loses sight of Georgiana's beautiful nature and bright spirit. Rather than attaining power over mortality by removing the birthmark, Aylmer's quest for perfection results in Georgiana's death.