Wood’s lamp is mainly used to diagnose pigment-altering diseases, skin infections and porphyrias. Pigment-altering diseases (a) Hypopigmentation and depigmentation: 1. Vitiligo: bright white fluorescence, contrast increase is obvious. 2, simple furfura: post-inflammatory depigmentation, contrast increase is not obvious. 3, nodular sclerosis, a pigmentless nevus: contrast increase is not obvious. 4, Ito pigmentation reduction: the contrast increases insignificantly. （Pigmentation: 1. Melasma: epidermal type, with obvious contrast increase. Dermal type, light blue under natural light, the color does not deepen when examined under Wood’s lamp. Nevus of Ota: contrast increase is not obvious. 3.Freckles: the contrast increases obviously. 4, Pigmented dry dermatosis: contrast increase is not obvious. 5.Coffee spots: the contrast is not obvious. Infectious diseases (a) bacteria 1, ringworm: show coral red fluorescence. 2, acne: show orange-red fluorescence, the intensity of fluorescence within the facial hair follicles and the number of Propionibacterium acnes has a significant relationship. Acne: show yellow-white fluorescence. 3.Pseudomonas aeruginosa infection: yellow-green fluorescence. 4, Axillary lichen planus: show dark green fluorescence. 5, Pseudomonas spp: show green fluorescence. (ii) Fungi: 1, dermatophytes: tinea capitis: specific fluorescence is seen in the follicles of broken hair or plucked hair. Bright green fluorescence is seen in Audu ounce, canine small, crooked, rust and plaster-like microsporidia infected individuals. Xanthophylls caused by Trichophyton mentagrophytes, on the other hand, may show faint blue fluorescence or dark green fluorescence. And the broken hair Trichophyton mentagrophytes and warty Trichophyton mentagrophytes do not occur fluorescence under Wood lamp. 2, ringworm: show yellow-white fluorescence or copper-orange yellow fluorescence. 3.Tinea versicolor: show bright green fluorescence. (iii) Others: 1, pubic lice: white fluorescence of the size of a pinhead overlying the pubic hair shaft. (2) Scabies: grayish tunnels are easily detected in the finger cracks, wrist side and male glans. In patients with porphyrin metabolism anomalous disease delayed cutaneous porphyria, their urine specimens show bright pink and orange fluorescence under Wood’s lamp. In congenital porphyria teeth, urine, and bone marrow may show red fluorescence. In erythropoietic protoporphyria, blood erythrocytes fluoresce briefly under a fluorescence microscope. And urine is non-fluorescent. Others 1. Squamous cell carcinoma: show bright red fluorescence. 2.Contact dermatitis: show the distribution of certain allergens in the skin.