Keratosis. Light micrograph (LM). Keratosis is a pre-cancerous area induced by ultraviolet light exposure, more common in fair-skinned people and those who are frequently in the sun. It can turn into a skin cancer called squamous cell carcinoma. Histologically, senile keratosis can show a variety of alterations such as epidermal thickening, hyperkeratosis, disordered epithelial layers, atypical keratinocytes with a loss of polarity, pleomorphism (variability in the size, shape and staining of cells), anaplasia (cells with poor cellular differentiation) ) and dermal lymphocyte infiltrates. Magnification: x 100 when printed at 10 centimetres high.