| dermatology | ARTICLE
high intensity blue light alone resulted in a significant reduction of 59–67% of inflammatory acne lesions29
. this
resulted in the Fda clearance of intense blue light alone as a treatment for acne30, 31
. the combination of blue and
red light (fluorescent lamps, led) in the treatment of acne was found to be effective8, 32
. light sources first used for Pdt were mainly
broadband light sources, in combination with systemically given photosensitisers. the use of topical ala for skin diseases during the 1980s overcame the problem of generalised cutaneous photosensitivity associated with systemic photosensitisers. topical ala has been used in combination with red and blue light. However, side-effects associated with its use include blistering and crusting33
. Second-generation
photosensitisers, such as ala and mal, have increased absorbance and therefore photoreactivity in the 650– 850 nm range. Porphyrins are the main photosensitisers used in Pdt, primarily with 360–400 nm, and less commonly with 600–635 nm. 5-ala is converted within the target cells to PpIX, which in turn has an absorption spectrum with a blue peak at 417 nm, and a small red peak at 650 nm. therefore, optimal light sources are those that emit wavelengths in the blue spectrum owing to their ideal absorption by porphyrins, and the red spectrum owing to its deeper penetrance, despite being absorbed to a lesser degree33
. lasers were introduced and reported extensively for
use with Pdt in the 1990s. they were mainly of red, and to a lesser extent blue, wavelengths7
. red (copper
vapour dye-630 nm, Nd:yag-630 nm, argon ion-dye-630 nm, argon pumped-dye laser-633 nm), and blue lasers have been used for topical ala–Pdt for the treatment of cutaneous cancers and acne vulgaris. Side-effects include crusting, blistering, pain, erythema, dyschromia (tanning-like reaction), and topical phototoxic reactions33
. lP Pdl (595 nm) has been used for topical ala–Pdt
for enhanced effectiveness and shortened downtimes owing to its better safety profile. the rationale for its use in Pdt is the absorption peak of PpIX at 575 nm. excellent cosmetic results have been reported with lP Pdl for acne treatment7
. other reports suggest that lasers are not
superior to other cheaper and more practical options such as broadband lamps and leds21
.
Photosensitising agents used in PDT for acne vulgaris ala and its methylated ester mal are prodrugs that are endogenously converted by the haem biosynthetic pathway to PpIX5
. the effect of topical Pdt depends on
the concentration of the precursor used, the time of application on the skin, whether skin occlusion is used, and the tissue oxygen availability, as well as the light wavelength and dosimetry22
. topical ala–Pdt has been shown to be effective in
acne. the mode of action of Pdt in acne includes: ■ Photodestruction of P. acnes, which accumulates porphyrins in the presence of ala10 ■ a selective action in the sebaceous glands, resulting in
prime-journal.com | July 2011
the reduction of both sebum production and sebaceous gland size, after illumination11 ■ reduction of follicular obstruction via its action on keratinocytes shedding and hyperkeratinisation34 Initially, the rationale of Pdt use for acne treatment
.
was based on the fact that P. acnes produces porphyrins, especially coproporphyrin III, in small quantities. Visible light may activate these porphyrins and induce a photodynamic reaction that can destroy bacteria (endogenous Pdt)35
. after illumination, the Pdt reaction
is induced in acne lesions, resulting in the production of oxygen species and bacterial destruction33
. However, the
reaction varies and is possibly related to the concentration and type of porphyrins in the follicles of the acne patient, as well as to the ability of light to penetrate in the skin and induce the photodynamic reaction17
. Blue light has been
found to have a lesser effectiveness for treating acne, possibly owing to reduced penetrance depth. on the other hand, red light, although less effective in photoactivation of porphyrin, is able to penetrate deeper, and has been shown to increase effectiveness in acne, in combination with blue light8
. the application of topical ala increases the
effectiveness of Pdt in acne treatment, as ala is selectively uptaken by the sebaceous follicles33
. topical
ala induces selective fluoresence of PpIX in acne lesions, with minimal localisation in the normal
Formation of skin pimples and acne
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