What is the term for a small blister or sac that contains clear fluid beneath the epidermis?

A vesicle is defined as a small blister or sac that contains clear fluid beneath the epidermis. This fluid-filled structure is typically less than 1 centimeter in diameter and is often seen in conditions such as herpes simplex or contact dermatitis.

In contrast, a papule is a small, raised area of skin that is usually solid and may vary in color. A cyst is a closed sac-like structure that can contain fluid, semi-solid material, or air but is located deeper in the skin than a vesicle. A pustule is also a type of blister but is characterized by a raised bump filled with pus, which gives it a yellowish appearance rather than being clear. Thus, the defining feature of a vesicle is the clarity of its fluid and its placement just under the epidermis.