Skin diseases are divided into 28 categories, 1016 diseases, 13 common categories and 6 most common categories. 1, infectious skin diseases Viral infectious skin diseases are divided into herpes virus and papilloma virus infection. The former has herpes simplex, genital herpes, chicken pox and shingles, the latter has common warts, warts, flat warts and condyloma acuminata; bacterial infectious skin disease is divided into coccidioides infectious skin disease, impetigo, folliculitis, boils, dengue and gonorrhea. Mycobacterial infectious skin diseases include leprosy and tuberculosis. Fungal infectious dermatoses include ringworm, ringworm, ringworm and nail fungus. 2.Allergic skin diseases contact allergic dermatitis, eczema, atopic dermatitis, urticaria and drug rash. 3.Erythematous scaly skin disease pityriasis rosea, psoriasis, pityriasis simplex, lichen planus, and seborrheic dermatitis. 4.Vasculitis and lipofuscinosis Allergic cutaneous vasculitis, allergic purpura, Sweet’s disease, leukodystrophy, pigmented purpuric dermatosis, erythema nodosum, Weber-Christan lipofuscinosis, nodular wandering lipofuscinosis, Rosman-Maki lipofuscinosis. 5.Dermal appendage diseases Acne and rosacea. 6.Pigmentary dermatoses are divided into pigment-increasing dermatoses and pigment-reducing dermatoses. The former are freckles, chloasma and nevus of Ota, while the latter are vitiligo, halo nevus, anemic nevus, depigmented nevus and senile leukoplakia.