Parakeratosis is a term used to describe the presence of a nucleus within a specialized skin cell called a keratinocyte. Skin is made up of several different layers of cells. The abnormal keratinocytes in parakeratosis are found in the outermost layer of the skin called the stratum corneum. Pathologists can see these keratinocytes when looking at a sample of skin under the microscope.
The nucleus is a specialized part of the cell that holds most of the cells’ genetic material. Normally as a keratinocyte develops and moves towards the outside surface of the skin, the nucleus is removed from the cell before it reaches the stratum corneum. For this reason, parakeratosis in the skin is an abnormal finding.
Parakeratosis can be seen in several inflammatory skin diseases such as psoriasis and spongiotic dermatitis (eczema). Parakeratosis can also be seen in some types of skin cancer such as squamous cell carcinoma and the precancerous condition squamous cell carcinoma in situ. Because parakeratosis can be seen in a variety of conditions, it is a description and not a diagnosis by itself. Pathologists use the presence of parakeratosis along with other features to make a final diagnosis.