Ultraviolet radiation (UVR, ‘sunlight’) may improve some skin diseases like psoriasis and eczema but confusingly may also exacerbate the same diseases and induce a number of specific dermatological conditions. This is usually attributable to ultraviolet-B (UVB) and untraviolet-A (UVA). UVB palys a major role in the induction of skin cancers while UVA majorly causes skin ageing. Determination of the waveband or wavebands that contribute to sensitivity may be clinically important. For instance, UVB does not pass through window glass whereas UVA does. The practical corolarry of this is that patients who are markedly UVA sensitive need to wear sunblock and be protected even when inside a car or inside a building where there is strong natural light.

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