The lesions may be keratinous protuberances are one of the main symptoms of actinic keratosis, the process of keratin formation in the stratum corneum is called keratinization it is the process of transformation from cellular proteins to keratin with completely different physicochemical properties. The process of keratinization includes protofibrillar degeneration of the cytoplasm and breakdown and disappearance of the cytoplasm and nucleus. Differential diagnosis of the disease is: 1, seborrheic keratosis: the surface of the greasy scales, soft mandarin surface smooth without hard cuticle, pathohistology and histology can be seen within the epidermis epidermal cyst formation. 2.Discoid lupus erythematosus: there are dilated follicular pores and follicular keratosis, and there is atrophy, lesions occur in the face, especially in the cheeks and nose, butterfly-shaped distribution. 3.Malignant nevus freckle-like nevus: occurring in the exposed parts, for the pigment spots, not higher than the skin surface can gradually expand, the diameter can be up to a few centimeters, for the brown or black long period of time about 1/3 of the damage can develop into malignant melanoma. 4.Others: attention should be paid to differentiate it from linear epidermal nevus and squamous cell carcinoma.