vesicle

A vesicle is a small, fluid-filled sac or pouch found in plants and animals. In biology, it can refer to a cyst, a vacuole, or a pocket of embryonic tissue that develops into an organ. A specific type of vesicle is a small elevation on the skin containing watery liquid, which is commonly known as a blister.1

Blisters are classified by size: vesicles are 0.5 cm or less in diameter, while larger ones are called bullae. They often form due to friction, separating skin layers and filling with fluid. Blisters can also be symptoms of skin conditions like contact dermatitis, infections, or autoimmune diseases. The fluid inside is usually clear, but can be yellowish if it contains pus or red if it contains blood.2