Sunlight exposure is believed to have a beneficial effect on some inflammatory skin conditions. It contains the ultraviolet electromagnetic spectrum, which can kill many organisms, and also has a broad spectrum of electromagnetic radiation. The most important spectrums of solar radiation which reach the surface of the earth are ultraviolet radiation, visible lights, infrared, and radio waves. However, there are many factors that influence the level of energy that reach us, such as area, time of the day, and climate. Artificial light source can help overcome this defect. Many studies show that artificial UV radiation can improve many skin conditions such as psoriasis and vitiligo.
Some patients report improvement of acne after exposure to sunlight [34-36] though some studies state that evidence for improvement of acne due to sunlight is lacking [37]. In addition, UV radiation has complications associated with it, such as erythema, sunburn, pigmentary alterations (prolong hyperpigmentation, melasma), photoaging, and the risk for the development of skin cancer [38].
The basic principle of photomedicine states that when chromophores (any molecule which can absorb some specific electromagnetic spectrum, such as light, and cause a reaction) receive light in the appropriate spectrum, they can produce a reaction which results in
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Figure 17.3 Excitation of protoporphyrin IX. |
changes within the surrounding chromophore area [39]. P acnes, which are involved in the pathogenesis of acne, can produce endogenous chromophores called porphyrins, mainly coproporphyrin III and protoporphyrin IX (Pp-IX) as part of its normal metabolic processes. Corpoporphyrin III can be seen on the face under 365 nm (UVA1- Wood’s lamp) (reddish-orange fluorescences). When these porphyrins (which can react to wavelengths that fall into the ultraviolet to visible light spectrum, but peak at the Soret band of blue light at 400-420 nm) are stimulated by light; this leads to photoexcitation, and the formation of singlet oxygen-free radicals that cause destruction of P. acnes [40,41]. Blue light systems are used based on this theory, and many studies prove their efficacy.