Which of the following is an example of a primary lesion?

A primary lesion is a term used in dermatology to describe the initial stage or form that a skin condition takes, which can be recognized and classified. Bullae are a type of primary lesion characterized by large fluid-filled blisters that can occur due to friction, burns, or certain skin conditions. They are important to identify, as they indicate the early phase of a skin reaction or condition.

In contrast, scales, crusts, and scars represent secondary lesions. Scales are formed when the outer layer of the skin sheds and can be a sign of conditions like psoriasis. Crusts are formed when a liquid, such as pus or serum, dries on the skin surface, while scars refer to the mark left on the skin after a wound has healed, representing a change in the skin's structure due to damage. Thus, differentiating between primary and secondary lesions helps in diagnosis and determining appropriate treatment for various skin conditions.