Which type of lesions are characterized by a loss of the outer layer of skin?

The correct answer is erosions, which are defined by the loss of the outer layer of skin, specifically the epidermis. Erosions typically occur when the surface of the skin is lost due to the rupture of vesicles or bullae, leading to a moist, often red area that may be sensitive but usually does not involve the deeper layers of skin. Erosions can result from conditions such as blisters, scratches, or inflammatory processes that have caused the top layer of skin to peel away.

Pustules, on the other hand, are small elevations on the skin that are filled with pus, but they do not involve the loss of the skin's outer layer. Wheals are raised, itchy areas caused by an allergic reaction, characterized by swelling, but again, they do not indicate a loss of skin. Papules are small, solid bumps on the skin that do not involve ulceration or the loss of skin layers. Each of these other lesion types has distinct characteristics and implications in dermatology, but only erosions specifically relate to the loss of the outer skin layer.