How is "keratosis" defined?

Keratosis is defined as a growth of keratin on the skin, which often results in rough bumps or lesions. Keratin is a key structural protein that forms the primary component of the outer layer of skin, as well as hair and nails. When there is an excessive proliferation of keratinocytes, the skin cells that produce keratin, it leads to the thickening of the outer layer of the skin, resulting in the characteristic appearance of keratosis. This condition can manifest in different forms, such as seborrheic keratosis or actinic keratosis, which can vary in appearance but are generally associated with rough, raised patches on the skin's surface.

The other definitions provided do not accurately describe keratosis. For example, a fungus infection on the skin pertains to conditions like tinea or candidiasis, while allergic reactions typically involve inflammation and redness rather than the growth of keratin. Skin cancer represents a distinct category of malignant growths and is not synonymous with keratosis, although some forms of keratosis may carry a risk of progression to skin cancer if left untreated.