What condition is characterized by a thickening of the skin due to a mass of keratinized cells?

The condition characterized by a thickening of the skin due to a mass of keratinized cells is hyperkeratosis. This condition occurs when there is an overproduction of keratin, a type of protein that helps protect the skin. As a result, the outer layer of the skin becomes thickened, leading to rough and scaly patches. Hyperkeratosis can be a response to various stimuli, such as chronic friction, pressure, or irritation.

In contrast, dermatitis and eczema refer to inflammatory conditions of the skin, characterized by redness, swelling, and itching, rather than the specific thickening associated with hyperkeratosis. Psoriasis is a distinct autoimmune condition that also involves skin thickening and scaling, but it is driven by an overactive immune response and leads to other symptoms such as plaques and may involve joint pain. Hyperkeratosis is specifically about the thickening due to keratin accumulation, which is why it is the correct answer.