Hyperkeratosis refers to an abnormal thickening of the stratum corneum, a pathological change in which the epithelial cells on the surface of the skin or mucous membranes become hyperkeratotic and the stratum corneum becomes inflamed and thickened. The following is the specific differential diagnosis. 1, echinoderm hypertrophy type For the most common type of this disease, hyperkeratosis and papillomatosis are often mild, but the epidermis is significantly thickened. In some cases the thickened epidermis though only envelops the narrow papillae. In other cases, a reticular appearance consisting of thickened, intertwined cords of epidermal cells surrounding islands of connective tissue is seen. Many keratotic depressions may be seen in cross-section as numerous pseudoceratocysts. Also seen are true cysts that are abruptly and completely keratinized, with basal cells outnumbering squamous epidermis in a significantly thickened epidermis. The melanin content of this type is more than normal. 2, hyperkeratosis type Also known as finger-like or serrated type, hyperkeratosis and papilloma-like proliferation is obvious, but spine layer hypertrophy is not very obvious. Many of the dermal papillae on the surface of the epidermis are covered with epidermis and extend upward in a finger-like manner, like the roof of a church. The epidermis is mostly composed of squamous epidermis, but small clusters of basal-like cells are seen everywhere, and there is usually no large amount of melanin. 3, glandular type The epidermis shows many thin epidermal cell bundles extending from the epidermis to the dermis and branching and intertwining, many bundles consist of only two layers of basal-like cells. Pure reticular damage without keratinocysts and pseudo-keratinocysts. However, the glandular type is also often accompanied by the spiny layer hypertrophy type, the latter commonly has keratocysts and pseudo-keratocysts, and the basal-like cells of the glandular type commonly have a marked increase in pigmentation. 4. Colony type There are highly prominent cell nests within the epidermis, the latter in some cases being deeply stained due to small nuclei, and intercellular bridges are seen only in a few areas, while resembling the foci of basal cell epithelioma. In some cases, the cell nests consist of rather large cells with obvious intercellular bridges. 5.Stimulated type This type is characterized by the presence of many squamous vortices or squamous beads composed of many eosinophilic flat squamous cells arranged in an onion-like pattern. Therefore, they resemble poorly differentiated keratinized beads. However, these squamous swirls, which are small and numerous, are easily distinguished from the keratinized beads of squamous cell carcinoma by their restricted nature. In addition, irritated seborrheic keratosis can grow downward and exceed the horizontal demarcation line usually seen in non-irritated type. 6.Echinocytoma nigricans is a rather rare histological type of seborrheic keratosis with many large melanocytes filled with melanin scattered within the damage. Silver-stained these cells have large dendrites and contain a considerable amount of melanin, whereas keratin-forming cells contain hardly any melanin. This type differs from the usual pigmented seborrheic keratosis, which has only a few melanocytes, with melanin located almost entirely within the keratin-forming cells.