Wood’s light: How does it work ?

What happens

• light is shone on to the skin
• this causes the collagen in the dermis to fluoresce.

Examples

• In vitiligo, the lesions are devoid of melanin and therefore lesions are very visible wheareas the surrounding skin appears dark due to the inability of light to fluoresce.

• In melasma:

1. If the melanin is epidermal, the light will appear stronger as the dermal collagen bundles will fluoresce. (the melanin which is only localized in melanocytes (and a few keratinocytes) will NOT stop the light) = pigmentation is enhanced. Lesions appear dark brown and well delineated.
2. If the melanin is dermal, it will filter the light so that the collagen fibres will fluoresce less and won’t be reflected (the melanin in the dermis is diffuse and will absord the light before it reaches the collagen bundles) = pigmentation appears reduced. Lesions appear brown-grey and are poorly delineated.

Contributors:

Dr Christophe HSU – dermatologist. Geneva, Switzerland

Bibliography: Disorders of Pigmentation. 70th Annual Meeting of the AAD (American Academy of Dermatology) – San Diego, California, United States of America (USA)