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Avci et al. Page 3 Although LLLT is now used to treat a wide variety of ailments, it remains somewhat controversial as a therapy for 2 principle reasons. First, there are uncertainties about the fundamental molecular and cellular mechanisms responsible for transducing signals from the photons incident on the cells to the biological effects that take place in the irradiated tissue. Second, there are significant variations in terms of dosimetry parameters: wavelength, irradiance or power density, pulse structure, coherence, polarization, energy, fluence, irradiation time, contact vs non-contact application, and repetition regimen. Lower dosimetric parameters can result in reduced effectiveness of the treatment and higher ones can lead to tissue damage.1 This illustrates the concept of the biphasic dose response that has been reported to operate in LLLT 1,18,19. Many of the published studies on LLLT include negative results. It is possibly because of an inappropriate choice of light source and dosage. It may also be due to inappropriate preparation of the patient’s skin before application of LLLT, such as: lack of removal of makeup and oily debris, which can interfere with the penetration of the light source, and failure to account for skin pigmentation.17 Inappropriate maintenance of the LLLT equipment can reduce its performance and interfere with clinical results as well. It is important to consider that there is an optimal dose of light for any particular application. Laser radiation or non-coherent light has a wavelength and radiant exposure dependent capability to alter cellular behavior in the absence of significant heating.20 Phototherapy employs light with wavelengths between 390–1,100 nm and can be continuous wave or pulsed. In normal circumstances, it uses relatively low fluences (0.04–50 J/cm2) and power densities (< 100 mW/cm2).21 Wavelengths in the range of 390 nm to 600 nm are used to treat superficial tissue, and longer wavelengths in the range of 600nm to 1,100nm, which penetrate further, are used to treat deeper-seated tissues (Figure 2).4 Wavelengths in the range 700 nm to 750 nm have been found to have limited biochemical activity and are therefore not often used.1 Various light sources used in LLLT include inert gas lasers and semiconductor laser diodes such as helium neon (HeNe; 633 nm), ruby (694 nm), argon (488 and 514 nm), krypton (521, 530, 568, 647 nm), gallium arsenide (GaAs; > 760 nm, with a common example of 904 nm), and gallium aluminum arsenide (GaAlAs; 612–870 nm).17 A wide range of LED semiconductors are available at lower wavelengths, whose medium contains the elements indium, phosphide and nitride. One question that has not yet been conclusively answered is whether there is any advantage to using coherent laser light over non-coherent LED light.22 While some medical practitioners treat deep tissue lesions using focused lasers in “points”, in dermatology the use of LEDs is becoming increasingly common due to the relatively large areas of tissue that require irradiation. LLLT for Skin Rejuvenation Skin starts showing its first signs of aging in the late 20s to early 30s and it usually presents with wrinkles, dyspigmentation, telangiectasia, and loss of elasticity. Common histologic and molecular-level features are reduction in the amount of collagen, fragmentation of collagen fibers, elastotic degeneration of elastic fibers, upregulation of matrix metalloproteinases (MMPs), especially MMP-1 and MMP-2, dilated and tortuous dermal vessels, and atrophy and disorientation of the epidermis.23,24 Both chronological and Semin Cutan Med Surg. Author manuscript; available in PMC 2014 August 08. NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptPDF Image | Low-level laser (light) therapy (LLLT) in skin: stimulating, healing, restoring
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