4th July 2023

Background

Photosensitivity describes a group of symptoms, diseases and conditions that are exacerbated by sunlight. Photodermatosis is a rash caused by photosensitivity, whereas it is called photodermatitis if the rash is eczematous. There are many different classifications of photosensitive rashes:

• Primary – exposure to sun causes a specific disease, e.g. polymorphic light eruption, solar urticaria, juvenile spring eruption
• Exogenous – photodermatoses rash is caused by an external photosensitiser such as food, drug or chemical that increases sensitivity to light, e.g. thiazide, tetracycline, NSAID, quinine
• Metabolic – the photodermatitis is caused by a metabolic defect, e.g. porphyria cutanea tarda
• Genetic – associated with a genetic disorder, e.g. xeroderma pigmentosum

Light Spectrum

Image Source: Flickr (2020). Light spectrum, Licensed under a creative commons licence. Available for free at: https://www.flickr.com/photos/rosenfeldmedia/49781640696 (Accessed on: 1 April 2022).