Question: what is a major difference between a vesicle and a wheal?
Answer: A bulla is essentially a large vesicle. It is a circumscribed collection of free fluid that is greater than 0.5 centimeters in diameter. What is the definition of a wheal? A wheal is a firm, edematous plaque resulting from infiltration of the dermis with fluid, wheals are transient and only last for a few hours.