Low Level Laser Therapy
Low-level laser (light) therapy (LLLT) is a fast-growing technology used to treat a multitude of conditions that require stimulation of healing, relief of pain and inflammation, and restoration of function. Although the skin is the organ that is naturally exposed to light more than any other organ, it still responds well to red and near-infrared wavelengths. The photons are absorbed by mitochondrial chromophores in skin cells. Consequently electron transport, adenosine triphosphate (ATP) nitric oxide release, blood flow, reactive oxygen species increase and diverse signaling pathways get activated. Stem cells can be activated allowing increased tissue repair and healing. In dermatology, LLLT has beneficial effects on wrinkles, acne scars, hypertrophic scars, and healing of burns. LLLT can reduce UV damage both as a treatment and as a prophylaxis. In pigmentary disorders such as vitiligo, LLLT can increase pigmentation by stimulating melanocyte proliferation and reduce depigmentation by inhibiting autoimmunity. Inflammatory diseases such as psoriasis and acne can also benefit. The non-invasive nature and almost complete absence of side-effects encourages further testing in dermatology.
Increasingly, non-invasive therapies for skin disease and skin rejuvenation are used, especially in Western countries where relatively high disposable incomes are combined with the desire for an ideal appearance fostered by societal pressures. Although the skin is the organ that is naturally most exposed to light, it still responds well to red and near-infrared wavelengths delivered at the correct parameters with therapeutic intent. Low-level laser therapy (LLLT) was discovered in the late 1960s, but only in recent times has it been widely applied in dermatology. The introduction of light emitting diode (LED) devices has reduced many of the concerns formerly associated with lasers, such as expense, safety concerns and the need for trained personnel to operate them. In fact, many LED devices are designed for home use and are widely sold on the internet. This review will cover the use of LLLT as possibly the ultimate non-invasive approach to treating the skin.
Low-Level Laser (Light) Therapy and Its Mechanism of Action
LLLT, phototherapy or photobiomodulation refers to the use of photons at a non-thermal irradiance to alter biological activity. LLLT uses either coherent light sources (lasers) or non-coherent light sources consisting of filtered lamps or light-emitting diodes (LED) or, on occasion, a combination of both. The main medical applications of LLLT are reducing pain and inflammation, augmenting tissue repair and promoting regeneration of different tissues and nerves, and preventing tissue damage in situations where it is likely to occur. In the last few decades, non-ablative laser therapies have been used increasingly for the aesthetic treatment of fine wrinkles, photoaged skin and scars, a process known as photorejuvenation. More recently, this approach has also been used for inflammatory acne. LLLT involves exposing cells or tissue to low-levels of red and near infrared (NIR) light. This process is referred to as ‘low-level’ because the energy or power densities employed are low compared to other forms of laser therapy such as ablation, cutting, and thermally coagulating tissue. Recently, medical treatment with LLLT at various intensities has been found to stimulate or inhibit an assortment of cellular processes.
The mechanism associated with the cellular photobiostimulation by LLLT is not yet fully understood. From observation, it appears that LLLT has a wide range of effects at the molecular, cellular, and tissue levels. The basic biological mechanism behind the effects of LLLT is thought to be through absorption of red and NIR light by mitochondrial chromophores, in particular cytochrome c oxidase (CCO) which is contained in the respiratory chain located within the mitochondria, and perhaps also by photo-acceptors in the plasma membrane of cells. Consequently a cascade of events occur in the mitochondria, leading to bio-stimulation of various processes. Absorption spectra obtained for CCO in different oxidation states were recorded and found to be very similar to the action spectra for biological responses to the light. It is hypothesized that this absorption of light energy may cause photodissociation of inhibitory nitric oxide from CCO leading to enhancement of enzyme activity, electron transport, mitochondrial respiration and adenosine triphosphate (ATP) production. In turn, LLLT alters the cellular redox state which induces the activation of numerous intracellular signaling pathways, and alters the affinity of transcription factors concerned with cell proliferation, survival, tissue repair and regeneration.
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. This illustrates the concept of the biphasic dose response that has been reported to operate in LLLT. 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. 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. 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).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. Wavelengths in the range 700 nm to 750 nm have been found to have limited biochemical activity and are therefore not often used. 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). 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. 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.