What is a fissure in the skin?

A fissure in the skin refers to a deep crack or break that extends into the dermis, making option B the correct choice. Fissures can result from various factors, including dry skin, fungal infections, or conditions that cause the skin to lose its elasticity, which can lead to painful splits. They may be seen in different dermatological conditions, especially where the skin is subjected to stresses that facilitate cracking.

In contrast, other options relate to different skin issues or conditions. Acne is a skin condition that arises when hair follicles become clogged with oil and dead skin cells. Eczema, on the other hand, typically presents with inflamed, red, and itchy skin, and while it may involve cracks, it is not specifically defined by them. Reactions to allergens involve various symptoms, usually manifested as rashes, itching, or swelling, but they do not specifically describe a physiological crack in the skin. Therefore, understanding the unique definition and implications of a fissure distinctly sets it apart from other skin conditions and symptoms.