What describes a condition where there is an excess production of keratin leading to thickened skin?

The condition characterized by an excess production of keratin, resulting in thickened skin, is known as keratosis. This term refers specifically to a group of skin disorders where keratin, the protein that helps make up the skin, hair, and nails, is produced in higher-than-normal amounts. A common manifestation of keratosis is the development of thick, often rough patches on the skin, which can be associated with various types of keratin build-up, such as actinic keratosis or seborrheic keratosis.

Other terms in the options describe different conditions. Erythema refers to redness of the skin due to capillary dilation, which does not involve keratin production. A nevus, commonly known as a mole, is a localized growth of melanocytes and does not pertain to keratin levels in the skin. A papule indicates a small, raised, solid pimple or swelling in the skin, which might not be related to keratin production at all and can represent various dermatological conditions. Thus, keratosis is the most accurate term for describing the effect of excessive keratin production leading to thicker skin.