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A second-degree burn is characterized by the presence of blisters. These burns affect both the outer layer of skin (epidermis) and the underlying layer (dermis), leading to swelling, redness, and pain. The formation of blisters is a protective response from the body, designed to shield the underlying tissues from further damage and infection.

In contrast, a first-degree burn, which affects only the epidermis, typically results in redness and minor swelling but does not cause blisters. Third-degree burns are more severe and extend through the dermis, potentially damaging deeper tissues; they can appear white, blackened, or charred, and blisters are usually absent due to the destruction of skin layers. Fourth-degree burns extend even deeper, affecting muscles and bones, and also do not present blistering. Thus, second-degree burns are specifically identified by the presence of blisters as a significant sign of damage to the epidermis and dermis.