Bulla is a large blister containing:

• A. Opaque sebum
• B. Blood and lymph
• C. Clear, watery fluid
• D. Pus

Answer: (C)

A bulla is a large fluid-filled blister whose contents are serous fluid—a thin, clear, watery liquid that leaks into a split in the epidermis from nearby capillaries. This makes sense because bullae form when layers of the skin separate and fluid from the surrounding tissue accumulates, but without introducing cells like neutrophils or red blood cells. That’s why pus (which is thick and cloudy) and blood (which would indicate a hemorrhagic blister) aren’t the typical contents. Opaque sebum isn’t a blister fluid either; it’s an oily substance produced by sebaceous glands. So the hallmark is clear, watery fluid.