Which condition is characterized by the thickening of the skin due to excessive growth of skin cells?

The condition characterized by the thickening of the skin due to excessive growth of skin cells is hyperkeratosis. This process occurs when there is an overproduction of keratin, the protein that forms the outer layer of the skin. Hyperkeratosis can manifest in various ways, such as calluses or thickened areas of the skin that appear as rough patches. It is often a response to friction, pressure, or irritation, leading to protective skin growth.

Other conditions, such as psoriasis and eczema, can exhibit skin thickening as well, but they also involve other symptoms and underlying inflammatory processes. Psoriasis, for instance, is an autoimmune disease that leads to rapid skin cell turnover and may result in scaly patches, while eczema is primarily characterized by inflammation and itching. Dermatitis generally refers to inflammation of the skin triggered by irritants or allergens, without necessarily causing the specific thickening seen in hyperkeratosis. Thus, hyperkeratosis is the most accurate definition of skin thickening due to excessive growth of skin cells.