What is the primary characteristic of a vesicle?

The primary characteristic of a vesicle is that it contains clear fluid. Vesicles are small, fluid-filled sacs found within or on the surface of the skin. They typically arise due to various conditions, such as infections or allergic reactions, and they have a well-defined border. Their clear fluid distinguishes them from other types of lesions, which may contain pus or other substances.

Other options describe characteristics of different skin conditions. For instance, pus-filled lesions are indicative of pustules rather than vesicles. Swellings above the skin could refer to a range of other lesions, including papules or plaques. Loss of pigmentation pertains to conditions affecting skin color, distinct from fluid-filled formations. Understanding these distinctions helps in accurately identifying skin lesions in clinical coding and diagnostics.