What condition is defined as infections and inflammation of deep skin structures?

The condition defined as infections and inflammation of deep skin structures is cellulitis. This condition occurs when bacteria penetrate the skin, often through a break or wound, leading to an infection that causes inflammation in the deeper layers of the skin and subcutaneous tissues. Symptoms typically include redness, swelling, warmth, and pain in the affected area, and it can spread rapidly without adequate treatment, making timely medical attention crucial.

The other conditions listed do not fit this definition. Dermatitis is a general term that describes inflammation of the skin but is not primarily characterized by infections affecting deeper structures. Eczema refers to a group of conditions that cause the skin to become inflamed or irritated, but it does not specifically denote an infection. Similarly, psoriasis is a chronic autoimmune condition that leads to the rapid growth of skin cells, resulting in scaling and inflammation but does not involve infection of deep skin structures. Hence, cellulitis is the specific condition that matches the description provided in the question.