It has long been known that red or near-infrared laser light promotes tissue repair and regeneration and low-intensity light called low-level laser therapy (LLLT) stimulates cellular activity. The most commonly used devices have wavelengths in the range 500–1,100 nm (the so-called optical window of tissue) and they deliver fluences of 1–10 J/cm2 with a power density of 3–90 mW/cm2. LLLT has shown beneficial effects for a variety of medical conditions such as wound healing, nerve regeneration, joint pain relief, stroke recovery, and the prevention and treatment of mucositis. The ability of lasers to induce hair growth was incidentally noted as early as 1967 when Mester et al. used low-level laser therapy (LLLT) to treat cancer in mice with shaved backs. Dr. Mester applied a ruby laser beam of 694nm to the backs of shaved mice, seeking to evaluate potential carcinogenic changes, when he noted instead more rapid regrowth of hair. Since then, hypertrichosis (increased hair growth) has been recognized to be a possible side-effect of laser treatment.
Recently, attention has been drawn towards an uncommon but striking adverse effect of lasers being used for hair removal. It has been noticed in some cases that, increase in hair density, color or coarseness or a combination of these occurs at or around sites treated for hair removal. The name given for this phenomenon is “Paradoxical Hypertrichosis” and the incidence varies from 0.6% to 10%.
Laser light generated by low-powered (cold) lasers has recently come into use as a non-surgical hair restoration treatment for pattern hair loss. Hand-held “comb”, “brush” or “cap” laser devices are marketed for use at home. Larger “hood” or “cap” devices are used in hair restoration clinics.The “cold” lasers used as a hair replacement therapy for the treatment of pattern hair loss deliver what is called low-level laser therapy (LLLT). The LLLT lasers are called “cold” because their light is absorbed by target tissue but does not heat the target tissue as occurs with lasers used to cut and remodel tissue.
Low Level Laser Light and Mechanisms of Cell Biostimulation
Laser phototherapy is assumed to stimulate anagen re-entry in telogen hair follicles, prolong duration of anagen phase, and increase rates of proliferation in active anagen hair follicles and to prevent premature catagen development.
Low level laser light is defined in part by its wavelength which is visible light in the 500nm-1100nm wavelength range, and this determines its properties of tissue absorption. The other characteristic is low power and low power density ensures a low thermal output and prevents tissue heating. Maintaining low power in LLLT devices helps avoid thermal injury to tissue and allows the opportunity for photostimulation to occur. The first law of photobiomodulation states that a cell must have a chromophore or photoacceptor that absorbs light photons in order to stimulate a biologic response. The most common photoacceptors in tissue are melanin, hemoglobin (oxyhemoglobinanddeoxyhemoglobin), and water. These are well known to doctors who may have lasers for hair removal or other cosmetic uses as these are targets for laser light. However, these chromophores actually have their lowest rate of absorption of light for the above range of wavelengths, thus creating what is referred to as the “optical window,” because with minimum absorption by these chromophores, the light wave can be absorbed elsewhere for its biostimulating effects to occur.
Studies reveal the cellular organelles involved in low level laser biostimulation are the mitochondria. Specifically, a portion of that organelle’s energy and respiratory chain contains a chromophore called cytochrome c oxidase—it is the last step in the electron transport system of the mitochondria. Evidence suggests that LLLT acts on the mitochondria and may alter cell metabolism by photodissociation of inhibitory nitric oxide (NO) from cytochrome c oxidase (CCO), causing increased ATP production, modulation of reactive oxygen species, and induction of transcription factors such as nuclear factor kappa B, and hypoxia-inducible factor-1. These transcription factors in return cause protein synthesis that triggers further effects down-stream, such as increased cell proliferation and migration, alteration in the levels of cytokines, growth factors and inflammatory mediators, and increased tissue oxygenation. Weiss and coworkers, by using RT-PCR and microarray analysis, demonstrated that depending on the treatment parameters, LLLT modulates 5-α reductase expression, which converts testosterone into DHT, alters vascular endothelial growth factor gene expression as wells as matrix metalloproteinase (MMP-2) which have significant roles in hair follicle growth, and in turn the group reported stimulation of hair growth on human dermal papillae cells.
Moreover LLLT may cause vasodilation and increased blood flow which was reported in several studies. Yamazaki and coworkers observed an upregulation of hepatocyte growth factor (HGF) and HGF activator expression following irradiation of the backs of Sprague Dawley rats with linear polarized infrared laser.
While the effects of these biochemical and cellular changes have broadly been studied in both animal models and clinical studies with patients, and have shown benefits in diverse conditions, such as increased healing in chronic wounds, improvements in sports injuries and carpal tunnel syndrome, pain reduction in arthritis and neuropathies, and amelioration of damage after heart attacks, stroke, nerve injury and retinal toxicity, [7, 9] the effects on hair growth stimulation have only recently gained the attention of the scientific community.
Safety and Possible Side Effects
A 510(K) is a premarket submission made to FDA to demonstrate that the device to be marketed is at least as safe and effective, that is, substantially equivalent, to a legally marketed device that is not subject to premarket approval.
A 510(k) clearance is often granted to devices that can show that they are technically and functionally similar to or as safe as an already legally marketed and distributed medical device, known as the “predicate” device. Often, it is not necessary for a 510(k)-cleared device to provide any evidence of efficacy—and most of the currently 510(k) cleared LLLT devices for hair loss treatment have not provided published clinical data. For this reason, it is only accurate to refer to these devices as “cleared” for safety, rather than FDA “approved.” Websites that suggest their device has been approved are inaccurate and potentially misleading to the public who are unaware of the difference between premarket approval and 510(k) clearance.
LLLT has demonstrated a remarkably low incidence of adverse effects when it has been used over 50 years for diverse medical conditions and in a variety of anatomical sites. In the specific area of LLLT for hair growth, the only adverse reports in humans, was the temporary onset of TE developing in the first 1–2 months after commencing LaserComb treatment, but disappearing on continued application. Some other possible considerations are presence of dysplastic or malignant lesions on the scalp which could be stimulated to grow by proliferative effects of LLLT.
LLLT can be used safely in conjunction with other medications including Propecia and Rogaine and there are no contraindications which would interfere with hair transplant surgery.
Low-Level Laser Therapy is useful for hair loss in men and in women where the thinning tends to be diffuse. These low-level laser devices appear to be safe and have been FDA approved for the treatment of androgenetic hair loss. Although their short-term usefulness has been validated in multiple studies, their long-term effectiveness has yet to be determined.
While mechanisms are still emerging, LLLT may increase anagen hairs through release of NO from CCO by photodissociation and LLLT may reduce inflammation in AA. However, more studies are needed to optimize treatment parameters and determine long-term efficacy as well as safety of emerging LLLT technologies. Most studies investigating effects of LLLT on hair growth have used wavelengths that range from 635 to 650 nm, but as of today no study has compared the effect of near-infrared wavelengths such as 810 nm, which have deeper penetrating capacities, to red light. Moreover, further studies are required to compare efficacy of different light sources (continuous vs. pulsed) and methods of light delivery (laser vs. LED).