Looking for a grey needle in a ‘hair’ stack! Using a Wood’s lamp for evaluating canities
How to cite this article: Kaliyadan F, Jayasree P, Ashique KT. Looking for a grey needle in a ‘hair’ stack! Using a Wood’s lamp for evaluating canities. Indian J Dermatol Venereol Leprol 2023;89:636–7.
Young patients who present with early onset greying of hair require a proper evaluation to assess the extent and number of grey hair. This is often difficult if the grey hair are few in number, in patients with darker skin types and a lighter shade of hair colour (brown/brown-black) or when hair colour has been used.
The Wood’s lamp is a handy device, widely used in dermatology practice, to aid in the diagnosis of pigmentary disorders and certain fungal infections. The principle of its use in pigmentary disorders is that melanin absorbs the ultraviolet spectrum emitted by Wood’s lamp, and thereby reduces the intensity of the fluorescence.1
We have observed that the same principle can be applied to hair devoid of melanin. Under Wood’s lamp, grey hair (partial, complete and even coloured) stand out compared to normally pigmented hair [Figures 1a and 1b]. This phenomenon can be used in the evaluation of conditions like premature canities and also possibly to assess the regrowth in alopecia areata (where the new hair tend to be lighter in colour). The main limitation is that this does not work well in people with blonde hair. An additional benefit is that when documenting grey hair, the images are clearer than natural light photography because the reflections from the hair surface often make it difficult to distinguish true grey hair [Figures 2 and 3].
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