Dermatology - Vesicles and Bullae

Dermatology - Vesicles and Bullae 
Vesicle is derived from the Latin word "vesicula," which means "little bladder," while bulla is derived from the Latin word "bulla," which means "bubble."
 A skin eruption characterized by the presence of small fluid-filled sacs is referred to as a vesicular exanthem, whereas a skin eruption characterized by the presence of large fluid-filled sacs is referred to as a bullous exanthem.
 A vesicle is a small cavity, measuring less than 0.5 cm, that is raised and contains fluid. On the other hand, a bulla is a larger cavity, measuring more than 0.5 cm, that is also raised and contains fluid.
One can feel vesicles and bulla upon palpation.
Vesicles exhibit a dome-shaped structure and can either be umbilicated (similar to herpes simplex) or flaccid.
Frequently, the roof of a vesicle or bulla is sufficiently thin to be translucent.

The contents of the vesicle/bulla are frequently visible. The vesicles containing serum exhibit a yellowish hue, whereas those containing blood range in color from red to black. Vesicles and bullae form as a result of a separation in different layers of the outermost layer of the skin. This separation might occur just below the top layer, inside the visible layer of the skin, or at the boundary between the outermost layer and the layer beneath it. As vesicles/bullae are consistently located near the surface, they possess a clear and distinct appearance.