The Wood lamp was invented in 1903 by American physicist Robert Williams Wood (1868-1953), and the Wood lamp uses a high-pressure mercury lamp as the emitting light source. nm, and the output power is generally I mW/cm2 . The melanin and collagen of epidermis and dermis absorb this wavelength. The blue light-based fluorescence can be emitted, but it is not characteristic. The fluorescence of the tissue itself depends mainly on the composition of elastic fibers (fluorophore is not yet known), collagen fibers (fluorophore is pyridine cross-linked), aromatic amino acids (fluorophore is dominated by tryptophan and its oxidation products), nicotinamide adenine dinucleotide and melanopsin precursors and their products. The actual use of the wood lamp does not require much skill, but it needs to be performed in a dark room. I, the diagnostic role of pigmented diseases 1, hypopigmentation and depigmentation Normally fair-skinned individuals identify hypopigmentation and depigmentation with the naked eye, which can be clearly visible under the w∞d light, manifesting as bright blue-white patches. Vitiligo: Examination with a w∞d lamp can help identify less obvious vitiligo lesions, especially in fair-skinned patients. Follicular pigmentation produced after oral photochemotherapy treatment can also be confirmed at an early stage by Wood’s lamp examination. Thus, it is useful for diagnosis and observation of the efficacy of treatment. Hypopigmented spots in tuberous sclerosis: Hypopigmented spots >10 mm in diameter, as oval or eucalyptus leaf-shaped white spots are the earliest cutaneous manifestations of tuberous sclerosis, and detection of these early lesions may alert the dermatologist to look more closely for other clinical manifestations that may aid in the diagnosis. Others can be used to confirm subtle hypopigmentation in pityriasis albuginea, lichen planus, and Ito hypopigmentation. 2.Pigmentation When the light from the wood lamp is irradiated to the melanin-rich epidermis most of it is absorbed, while it is scattered and reflected when irradiated to the adjacent skin containing less melanin, which forms a clear demarcation line at the junction of the two. Therefore, the wood lamp can be applied to help determine the subtle difference of pigmentation, which has been used clinically to classify melasma.1. Epidermal type Melasma deepens in color when examined by Wood lamp.2 Dermal type Melasma shows light blue color under natural light, but does not deepen in color when examined by Wood lamp.3. Mixed type patients show part of the lesions deepening in color, while the rest of the lesions do not deepen in color.4, The lesions of melasma patients with darker skin tone are more obvious under visible light than under ultraviolet light, so it is called Wood lamp non-display type. In addition, wood lamp can also be used as an effective method to observe the efficacy and prognosis of melasma. They can also be clearly shown under the wood lamp, which can help early diagnosis. The lesions of freckles and pigmented dry skin disease can also be identified with the help of woodlamp. The pigmentation of freckles can be darkened under woodlamp irradiation, while the pigmentation in the dermis, such as blue nevus, is not obvious. B. Judgment of infection 1. Bacterial infection can guide the early clinical diagnosis and the selection of appropriate antibiotic treatment. Pseudomonas spp.: in chronic ulcers and burns of the trauma. wood lamp can be used to detect early skin infection of Pseudomonas spp. especially the pathogenic bacteria of Pseudomonas spp. can produce Pseudomonas aeruginosa (Pseudomonas aeruginosa) fluorescein, which shows yellow-green fluorescence under wood lamp. Fluorescence can occur when the bacterial count is nearly 105/cm2. This is also the amount of bacteria required to cause infection. Therefore, the presence of fluorescence since indicates the possibility of a potential infection. The false-positive and false-negative rates are very low. w00d light can also be used to examine other Pseudomonas spp. infected skin conditions, including folliculitis and interdigital infections contracted through swimming and bathing. However, it should be noted that if the patient has recently washed the lesion, the result may be negative due to dilution of the fluorescent cords. Calf ulcers with bacterial infections can produce protoporphyrin and fecal porphyrins, which will fluoresce red under Wood’s lamp. Tinea rubra and Tinea axillaris: Tinea rubra is an infectious skin disease caused by Corynebacterium minimale. Because the pathogen can produce porphyrins, it fluoresces coral red under the w00d lamp. Axillary ringworm is an infectious disease of the skin caused by Corynebacterium slenderum, which fluoresces dark green under the Wood lamp. Propionibacterium acnes : It is known that orange-red fluorescence can be seen in the facial acne . The intensity of fluorescence in the facial follicles is significantly related to the number of Propionibacterium acnes. Because acne contains dense keratin, it often shows yellow-white fluorescence. Facial w∞d light examination is useful as a guide for those patients who have had poor results with oral antibiotics. 2. Fungal infections Dermatophytes: For oligodermal, nail and palmoplantar dermatophyte infections, Wcod light examination is usually not helpful for diagnosis because of the lack of fluorescence. It is particularly useful for the diagnosis of ringworm of the head, where characteristic fluorescence is seen in the follicles of broken or plucked hair. Tinea albuginea may be seen as bright green fluorescence; Tinea aureus may show faint blue fluorescence; and Tinea nigricans infection does not fluoresce. The fluorescence of diseased hair in general only indicates the presence of infection and usually does not distinguish the causative pathogen. It is also important to note that dressings, scales, ointments, and dry soap can cause false-positive fluorescence. In conclusion, the Wo0d light examination can help to differentiate ringworm and ringworm albicans and to determine the efficacy of the treatment, especially for contacts of ringworm. Ringworm: The Wood lamp is useful for examining the extent of lesions infected by Malassezia furfur. Wood’s lamp is particularly helpful in diagnosing follicular infections caused by such bacteria, and blue-white fluorescence can be seen in the hair follicles, so it is possible to distinguish Malassezia furfur folliculitis from other types of folliculitis. Wood lamp examination is particularly useful for the diagnosis of porphyria. Excess porphyrins can be detected in teeth as well as in urine, feces, and blood specimens. For example, urine specimens from patients with delayed cutaneous porphyrias show bright pink-orange fluorescence under the wood|light, and this reaction is more pronounced after the addition of 1.5 mol hydrochloric acid in the same volume. In various porphyrias, fluorescence in urine is mainly seen in the acute phase, while fluorescence in feces can even occur in remission. Examination of fecal specimens should be mixed with equal amounts of pentanol, glacial acetic acid, and ether to yield the best results and show coral-red fluorescence. In patients with congenital porphyrias, red fluorescence may be seen in their teeth, urine, and bone marrow. In erythropoietic protoporphyria, erythrocytes fluoresce briefly (10-15 s) orange-red under fluorescence microscopy. In contrast, urine is nonfluorescent. Biochemical screening tests can be completed selectively using a mixture of ether, glacial acetic acid, and hydrochloric acid. In patients with erythropoietic protoporphyria, strong red fluorescence is caused by excess protoporphyrin and fecal porphyrins. In acute intermittent porphyria, although metabolites are aggregated, they are not converted to porphyrins, so no fluorescence is observed. In acute intermittent porphyrias, there are metabolite aggregates, but they do not turn into porphyrins, so no fluorescence is observed. In addition, Wood’s lamp can be used for photodynamic diagnosis. Since porphyrin 5-aminolevulinic acid (5-ALA) derivatives accumulate in tumor tissues, the boundaries of recurrent basal cell epithelioma can be determined with Wood’s lamp after topical application of 5-ALA. Photodynamic diagnosis has also been used for other diseases such as heliokeratosis, Bowen’s disease, squamous cell carcinoma and extramammary Paget’s disease. In addition, when clinical distinction between melanoma, melanocytic hyperplasia and hematoma cannot be made, wood lamp examination can also be used. Melanoma and melanocytic hyperplasia appear black under Wood lamp, while hematoma is grape sprinkled red . Five, for the detection of drug fluorescence (1) contact allergens on the skin or supplies can emit fluorescence . Therefore, it can be clarified that contact dermatitis is caused by chemical substances. (2) Used to study the process of transfer to other parts of the body after local use of drugs. If there is a local deposit of tetracycline hydrochloride, the fluorescence changes from coral red to yellow after a few minutes of irradiation with a Wood lamp. In patients taking oral tetracycline, yellow fluorescence of the nail hallux and nail can be observed, which helps to distinguish whether the nail is hyperpigmented due to tetracycline or yellow nail due to other causes . Miparin hydrochloride (Adipine) can also produce yellow-green fluorescent nails. This method can be used to monitor patient compliance with oral administration of such medications. (3) Monitor the efficiency of topical dosing. For example, mineral oil on the skin , even after washing, can be detected in the hair follicles. When certain types of workers in the operation and can not wear gloves, protective cream can play a protective role. Recently, there have been reports of the use of od lights to monitor whether workers are applying protective creams at work. Sixth, other uses in the absence of other high-power UVA light source, Wood lamps can also be used for photosensitivity testing or light spot paste test light source. ManraSso et al. have reported that in 20% trichloroacetic acid or 70% hydroxyacetic acid increased salicylic acid or sodium fluorescein ratio (l:5 and l:15, respectively), under Wood lamp irradiation, salicylic acid produces green fluorescence. In contrast, fluorescein emitted yellow fluorescence. The authors concluded that this method helps to avoid overdosing and allows for uniform treatment of the entire treatment area, thus improving the safety of chemical peels. In addition, Wood’s lamp is occasionally recommended as a comfort treatment for pediatric patients with warts. This is because warts have a tendency to heal on their own. This painless and harmless method can be used for comfort treatment . In vitiligo, the lesions are small and inconspicuous under natural light Under Wood lamp, the lesions become large and conspicuous.