Bullae are large blisters on the skin that are filled with clear fluid. They can be caused by many different skin conditions.
Habif TM. Principles of diagnosis and anatomy. In: Habif TP, ed. . 5th ed. Philadelphia, Pa: Mosby Elsevier; 2009:chap 1.
Bullous pemphigoid, close-up of tense blisters
Poison ivy on the knee
Poison ivy on the leg