Wood's lamp

The examination with the Wood's lamp can be useful in some skin diseases such as micosis, vitiligo, erythrasma, melasma and some porphyrias. It is an inexpensive and non-invasive rapid test, though not very sensitive. In vitiligo it allows to highlight the characteristic milky white patches due to the loss of melanin. In acne a red-orange fluorescence proportional to the production of porphyrins produced by Cutibacterium acnes can sometimes be observed at follicular level. In the initial superficial chloasma, Wood's light accentuates the contrast between hyperpigmented skin and healthy skin, whereas in deep and old forms there is no contrast. A yellowish fluoresce is evident in case of infection with the yeast Malassezia furfur, greenish in presence of mycosis type tinea caused by dermatophytes and coral red in case of erythrasma.

The Wood's lamp has been used in dermatology for many years, it consists of a special lamp with a glass tube coloured entirely in purple by means of metal oxides, so as to retain a good part of the visible radiation and to produce an ultraviolet light invisible to the human eye (Wood's black light). As constructed, it emits a non-ionizing light with a wavelength between 340 nm (ultraviolet A) and 420 nm (visual radiation of violet-blue color), so as to make it easier to use in the clinic.