Specify the exact anatomical site of oral cancer most commonly associated with chronic ultraviolet light exposure.

The exact anatomical site of oral cancer most commonly associated with chronic ultraviolet light exposure is the vermilion border of the lower lip. The vermilion border is the distinct transitional zone where the reddish, moist tissue of the lip meets the surrounding drier skin of the face. The lower lip is disproportionately affected because its anatomical position subjects it to more direct and prolonged chronic sunlight exposure compared to the upper lip. This long-term ultraviolet radiation exposure causes cumulative DNA damage within the epithelial cells of the vermilion tissue, leading to an increased risk of malignant transformation, most commonly resulting in squamous cell carcinoma.