Final answer:
Keratosis leads to a thickening of the skin due to an overgrowth of keratinized cells in the stratum corneum.
Step-by-step explanation:
Keratosis affects the skin by causing it to become thick. The condition involves an overgrowth of the stratum corneum, which is the outermost layer of the epidermis consisting of dead skin cells. The epidermis is composed of keratinocytes that produce keratin, a fibrous protein that provides protection and waterproofing to the skin. Due to this overproduction of keratin, the surface of the skin with keratosis can become significantly thicker than normal, leading to a feeling of roughness or the appearance of lumps or ridges.