What is a vesicle?

A vesicle is characterized as a small collection of clear fluid, often referred to as a blister. This formation occurs when fluid builds up between the layers of the skin, resulting in a raised area that is typically less than 1 centimeter in diameter. Vesicles can be observed in various medical conditions, including infections and skin reactions, and serve as a protective mechanism for the underlying skin as the fluid-filled sac helps to cushion and heal the affected area.

The other options describe different skin lesions or abnormalities. A hard, raised lesion refers to a solid growth that can be associated with different dermatological issues but does not share the fluid-filled nature of a vesicle. An open sore akin to an ulcer indicates a different type of skin injury that tends to be deeper and involves the loss of skin integrity rather than the superficial fluid accumulation seen in vesicles. A lump caused by a polyp pertains to a growth that can occur in various tissues, typically more substantial than a vesicle and often related to internal developments rather than a surface-level fluid response. Thus, the clear fluid distinction is pivotal in defining a vesicle correctly.