Clinical aspects in Laser hair removal
Excess hair and/or unwanted hair are of significant medical, social and cultural importance and are there-fore the subject of much attention, manipulation and regard in both genders and all races. The multitude of treatments available is testimony to these facts. Traditionally, conditions such as hirsutism, hypertrichosis, and cosmetic elegance have been treated with electrolysis/thermolysis, tweezing, shaving, waxing and sugaring, plucking, threading, depilatories and X-raytherapy.1These methods, however, were found to be slow, tedious, painful, impractical for treating large areas, and, in most cases, temporary. Consequently, the need for a long-term, non-invasive, rapid, reliable and safe method became a necessity in our society. When first described some 7 years ago, laser hair removal created controversy.2As the technology matured, laser hair removal generated growing demand not only for a safe, non-invasive, pain-free procedure, but also for effective, rapid pace, easy to operate, and affordable technology. Today, photo epila-tion by laser and other light-based technology is the fastest growing procedure in modern cosmetic dermatology. As more clinical research and experience is gained in the field of laser hair removal, manufacturers and practitioners have been obligated to seek safer and more effective results. Although the technology is relatively new, it has already generated much interest among clinicians and patients alike because of its ability to delay hair regrowth, and non-invasively remove large areas of hair with minimal discomfort, and a low incidence ofcomplications.3However, efficacy and safety of hair removal by laser and light-based technology varies considerably among manufacturers due to differences inpatients’ skin–hair biology traits, optimization of electro-optical parameters and clinical protocols. The purpose of this review is to discuss the major scientific and clinical issues in the field of photo epilation that have evolved in the last decade. Pertaining to our discussion will be the following topics: hair biology; biomedical optics and laser physics; clinical experience with selected technologies; and essential issues in photo epilation.
A hair follicle consists of three regions: the in fundibulum, isthmus, and hair bulb. The general anatomy of hair follicle is shown in Figure1. The inferior segment of the hair follicle lies below the arrector pili muscle insertion and includes the hair bulb and dermal papilla. As will be discussed later, this area is of great importance in photo epilation. On average, the bulb is approximately 4mm in depth from the surface of the skin, a considerable depth of penetration required by the laser light-based systems.4The hair bulb is made up of germi-native matrix cells along with interspersed melanocytes. The dermal papilla, located in the base of the bulb, is fed by the blood stream, which carries nourishment to produce new hair. The bulge is located approximately one-third of the distance down from the skin surface to the follicle bulb. Dermal sheath cells and epidermal outer root cells are found in the follicle bulb. These cell types extend into the isthmus and infundibulum of the hair follicle and play an important role in hair growth. Human hair grows in a cyclic pattern. The cycle consists of a growth or anagen phase followed by intermediate degradation of a portion of the follicle, known as the catagen phase and then by a resting period when no growth occurs – the telogen phase.7Figure2 describes the three phases of the hair growth cycle. It appears that different areas of the body, in addition to having shorter anagen cycles, have varying percentages of hairs actually in the anagen phase. The anagen duration varies greatly depending on age, season, gender (anagen in thigh hair in men is 54 day sversus 22 days in women), body site, hormones and underling genetic susceptibilities.8The catagen phase is generally 3 weeks in duration whereas the telogen phase usually lasts approximately 3 months. At any given time, the majority of the hair follicles (80–85%)are in the anagen phase and the remaining follicles are either in the catagen phase (2%) or the telogen phase(10–15%).9,10TableI shows the duration and percentage of the hair cycle in relation to body areas. For effective hair removal a laser/light source should damage one or more growth centers of hair, and the pluripotential cells of the bulge, dermal papilla, and hair matrix must be treated in the anagen cycle. It is during the anagen phase that melanin production occurs and becomes part of the growing follicle. It is also in the anagen phase that damage can affect the structure theoretically responsible for hair generation. During the telogen phase, the dermal papilla moves upward toward the bulge region and stimulates the onset of the anagen phase. In this active growth phase, the papilla moves down away from the bulge mass and the hair matrix cells regress during the catagen phase. Thus, depending on the stage of the hair cycle, the distance between the bulge region and the dermal papilla varies along with the depth of the dermal papilla within the dermis. These structures represent targets for hair follicle damage, and relative movement with respect to the skin structure attenuate their photo thermal susceptibility to a fixed wavelength laser beam. Thus, to achieve long-term hair removal, it is essential to destroy the structures that are responsible for hair growth: the bulge and bulb.
Laser physics and skin optics in hair removal
Laser hair removal is a multifactorial process that involves complex photo thermal reaction via the epidermis–dermis matrix, aimed to cause hair follicle damage while sparing the epidermis.Thus,hair follicle radication by alaserlight source is a function of various laser (e.g. power, spot size,irradiation time and repetition rate) and tissue (absorption and scattering coefficients, density, heat capacity and thermal conductivity) parameters.12The laser source may be continuous mode or pulsed. A continuous mode laser emits a continuous stream of light as long as the medium is excited, resulting in heating and vaporization of the target tissue. Alternatively, a pulsed laser will emit light only in short amounts, which may vary from nanoseconds to as long as seconds. Various sources of laser/light-based technology exist, including continuous light, flash lamp, radiofrequency, high-voltage discharge, diodes and others. When the lasing medium is excited, the molecules are stimulated to a higher energy level. These excited molecules tend to decay spontaneously to their original lower energy level realizing a photon. All emitted photons bear a constant phase relationship with each other in both time and phase – coherency. In turn, all laser light photons travel in the same direction with low divergence – collimated. Finally, laser light has high irradiance, since all the light is concentrated into an arrow spatial band resulting in a high radiant power per unit area. Energy refers to the number of photons delivered and is measured in joules (J). Power is measured in watts(W) and refers to the delivery rate of energy (1W=1J/s).Fluence is the total energy delivered per unit area and is measured in J/cm2. Pulse duration is the amount of time laser energy is applied (ns, ms). The pulse frequency is measured in hertz (1Hz=1pulse/s). Wavelength is measured in nanometers (nm) and refers to the distance between the peaks of the light waves and is used to characterize the type of light (green, red, yellow).The technology employed for hair removal by lasers/light-based systems is based on the principle of selective photo thermolysis. According to this principle, selective thermal destruction of a target will occur if sufficient energy is delivered at a wavelength well absorbed by the target within a time period less than or equal to the thermal relaxation time (TRT) of the target.12The TRTis the time it takes for the target to cool (half of its baseline temperature) and transfer the heat to sur-rounding structures. Under these conditions, it is possible to selectively target structures (e.g. hair follicle)while sparing the surrounding structures or tissues. The target site for the selective destruction of hair follicle scan either be endogenous melanin or exogenous chromophore.
A corollary of selective photo thermolysis is thermo-kinetic selectivity. This theory proposes that for the same chromophore, a longer pulse duration allows in trapulse cooling of smaller targets more rapidly than larger targets. Longer pulse durations are predicted to limit thermal damage to the epidermis. If the pulse duration exceeds the thermal relaxation time of the basal cell layer (about 0.1ms) or entire epidermis (about10ms), these structures will cool as they are heated during the laser pulse. In other words, larger targets (hair follicles) can be selectively injured more than smaller targets of the same chromophore (epidermis).13Recently, a novel concept of laser hair removal uses the thermal damage time (TDT) rather than the traditional hair follicle TRT concept that has been described. Studies indicate that the ideal pulse duration for medium to coarse hair reduction may be longer than the TRT of the hair follicle. Since the melanin occupies a much smaller volume compared with the follicle, heat is conducted from the shaft and melanized portion of the bulb to surrounding structures according to the laws of thermal diffusion. It has been suggested that widening the pulse duration allows an increase in the threshold of epidermal damage. As we have learned more about the mechanism of hair removal, it has become evident that the true targets for permanent hair removal are located at a distance from the hair shaft, at the outer roots heath of the follicle (stem cells), and the base of the follicle. This important observation has required reconsideration as to the appropriate laser parameters, particularly pulse width and energy density.
particularly pulse width and energy density.14–16When considering photo thermal destruction of hair follicles, there are three parameters that need to be considered: wavelength, pulse duration, and fluence. The longer the wavelength, the deeper the laser light penetrates the skin. To damage hair follicles, laser light must be absorbed by a chromophore within the follicle. Most lasers target the endogenous chromophore melanin within the pigmented hair shaft by delivering red ornear-infrared wavelengths. Melanin is the primary light absorber in the optical window between 600nm and1100nm. Wavelengths in this range are poorly absorbedby competing chromophores such as hemoglobin and water and penetrate deeply into the dermis.17It should be remembered though that the absorption of light bymelanin decreases with longer wavelengths and thatoxy hemoglobin and melanin have similar absorption at wavelengths at 750–850nm.The ability of these wavelengths to damage hair correlates directly with the amount and type of melanin with in the follicle: pheomelan in and eumelanin. Dark hair that contains large amounts of eumelanin readilyabsorbs these wavelengths and is most susceptible to laser-induced damage.18In theory, the use of longer wavelengths increases the ratio of energy deposited in the dermis to the epidermis, which results in relative bulb heating and epidermis sparing. However, although there is more melanin absorption at a wavelength of755nm than 800nm, larger energy density (fluence) must be employed during 800nm than with a 755nmwavelength laser. In the case of brown and black hairs, where the target chromophore is eumelanin, long-pulsed diode lasers at a wavelength of 800nm were found to be safe and clinically effective.19The necessary energy density (i.e. fluence) for the coagulation of hair follicle is proportional to the hair shaft diameter, as long as the bulb and follicle thickness are proportionate to hair shaft diameter; the thinner the hair, the smaller the energy density level.20In general, the fluence of the laser should be greater than or equal to the threshold fluence for tissue destruction. To confine thermal damage to the hair follicle, the laser pulse duration should lie between the TRT for epidermis, which is approximately 3–10ms, and the TRT for the hair follicles which is approximately 40–100ms. Using this concept to deliver light of the right combination of wavelength, energy fluence, and pulse duration, it is possible to precisely target the hair follicle and improve long-term hair removal. The laser pulse width plays an important role in determining selective photo thermolysis. High energy, short pulses of laser light cause extremely rapid heating of the target, with a rapid expansion of the thermal plasma. If the pulse width is too long, however, there will be insufficient time for the heat to dissipate, and undesirable temperature increase will occur with thermal injury to non-follicular structures, which could result in scarring or irregularities in pigmentation.21Ideally, the spot size should be as large as possible to reduce scattering of the light. When light is applied to the skin using a small spot size, the scattering of photons diffuses the beam rapidly. The fluence decays very quickly as a function of depth, so that most of the energy is dissipated in radial directions (outwards) and cannot reach the hair bulbs. With a large spot size, light penetration is more efficient since the ‘source’ of photons has an almost planar geometry. In human skin, about 15–20% of incident light at 700nm penetrates to a depth of 3mm. Thus, by using a larger spot size scattering of light in the dermis is lessened, leading to a greater depth of penetration and a lower threshold fluence.
Essential issues in laser hair removal
Hair removal is an ambiguous term that may carry different meaning for the patient, the physician and the industry. ‘Permanent hair removal’ should be distinguished from ‘permanent hair reduction’. The former is defined as the long-term, stable reduction in the number of hairs regrowing after a treatment regime, which may include several sessions. The number of hairs regrowing must be stable over time greater than the duration of the complete growth cycle of hair follicles, which varies from 4 to 12 months according to body location. Permanent hair reduction, on the other hand, does not necessarily imply the elimination of all hairs in the treatment area. This means that although laser treatments with these devices will permanently reduce the total number of hairs, they will not result in a permanent removal of all hair. Complete hair loss refers to a lack of regrowing hairs (i.e. the number of regrowing hairs is reduced to zero). Complete hair loss may be either temporary or permanent. Laser treatment usually produces complete but temporary hair loss for 1–3months, followed by partial but permanent hair loss. Temporary growth delay seems to be caused by laser damage induction of the telogen phase. Permanent hair loss seems to be associated with miniaturization of hair follicles.
Optimal follicle damage
Which hair cycle phase is the most appropriate, and which follicular elements cause hair-shaft regeneration is a subject of debate. In mice, Lin and colleagues noted that during the anagen phase there was heterogeneous, but widespread injury to the epithelium, increasing with increasing fluence (1.47–3.26J/cm
2). However, no follicular damage was observed during the catagen or telogen phases at any of the fluences used. Full hair regrowth occurred 28–56 days after laser exposure administered during the catagen or telogen phases for all fluence levels. In contrast, regrowth after laser exposure in the anagen phase was fluence-dependent: hair regrowth was moderate (1.47J/cm2) and none
In humans it appears that the most essential variable is the presence of the pigmented hair shaft within the skin that functions as a chromophore. It is there fore likely that both anagen and telogen follicles are sensitive to laser treatment. Because the telogen bulb is high in the dermis one might argue that this would be the optimal time for treatment; however, the superficial location is undermined by the bulb being poorly melanized. In early anagen the bulb is well melanized and still fairly superficial; this may present the best time for treatment. If the damage is not permanent during this cycle, follicles move into the telogen stage as they fall out. Because the duration of the hair cycle differs for different body sites, repeat treatments are usually done when there is a wave of rapid hair regrowth or between 4 and 8 weeks.52Another issue is whether the hair follicle is able to regenerate from the bulge area if the papilla is destroyed by a photo thermal source. Some researchers claim that hair follicles can regenerate in the absence of the hairbulb,53,54while others maintain that the destruction of the hair papilla is essential for permanent epilation.55The recent bulge-activation hypothesis maintains that the bulge area of the outer root sheath near the arrector pili muscle insertion contains pluri potential cells, which contribute to the new hair matrix when induced by the dermal papillae during the late telogen phase.14Thus,injury to the stem cells in the bulge area would lead to follicular destruction.
Safety and skin color
Although numerous lasers are available for laser-assisted hair removal, their use in individuals with a dark skin type presents many challenges due to com-
petition from epidermal melanin. The ideal candidate for hair removal is a light-skinned individual with dark terminal hair. Dark skinned patients with high epider-mal melanin content are prone to adverse side effects ranging from immediate pain and pigmentary disturbances to scarring. Despite the selection of appropriate wavelengths and pulse widths of the targeted chromophore, there is light absorption by the overlying epider-mal melanin Short wavelength (694, 755nm) hair removal laser scan be quite successful in lighter skin types. However, laser hair removal in Asians can be difficult, and multiple treatments are usually required for effective treatment. Recently, Hussain et al56evaluated the safety and efficacy of alexandrite laser hair removal in 144 Asian subjects with Fitzpatrick skin types III–V. The authors reported that no individuals had scarring or long-term pigmentary changes and concluded that there does not appear to be an exact correlation in Asian skin between complications occurring after test patch treatment and those seen with subsequent treatments. In a multicenter prospective study, laser hair removal was associated with a low incidence of side effects that were self-limiting in the majority of cases. The highest incidence of side effects was seen in patients with darker skin treated with the long-pulsed ruby laser.57However,the parameters for laser hair removal emphasize use for Caucasians (Fitzpatrick skin types I, II, or III). The characteristics of oriental skin and hair are black, coarse hairs in darker skin (Fitzpatrick skin types IV or V) and therefore the hair is more difficult to remove by laser. Recently, Lu et al58report 146 oriental patients (156body sites) who underwent treatment with the long-pulsed alexandrite laser (755nm wavelength) depilation system. Minimal and transient complications were noted. In a retrospect study of 900 patients who under went laser-assisted hair removal, Nanni and Alster59founddirect association of skin type on the risk of side effects. TableIII describes selected adverse side effects that may occur during or following laser/light-based hair removal treatment. Adrian and Shay60studied laser hair removal in African-American patients with skin types V and VI. Histologic studies examined efficacy and side effects in an effort to optimize laser hair removal procedures in this patient population. It was found that both laser modes could be used safely in skin type V and VI African-American patients; however, longer pulse durations enabled the delivery of higher fluences with minor and acceptable postoperative complication profiles. In order to avoid thermal damage of the epidermal matrix, current laser and non-laser devices use various parameters of cooling means by different techniques. Currently popular cooling techniques include contact(circulating cold water at 2–6‡C or sapphire), cryogen cooling or forced flow of chilled air. In general, the rational of cooling the skin is to allow the delivery of higher fluences and short pulse widths into the hairfollicle.61During long pulse modes (w100ms), how-ever, the epidermis tolerates a narrower temperature gradient in respect of the cooling method applied. Thus, to achieve effective epidermal protection, the hair color(i.e. black, blond), skin type (Fitzpatrick skin types I–VI)and cooling types should be carefully considered. Since adverse side effects are directly correlated with skin type, with darker-skinned and tanned patients experiencing a much higher rate of complications, skin types IV–VI and tanned skin are best treated with a diode laser (800 nm)or a Nd:YAG (1064 nm) laser. A physician who has a good understanding of hair biology, laser optics, and patient skin phenotypes is able to improve patient outcome and reduce untoward adverse side effects. Nevertheless, no system can provide fully predictable results.
Factors that affect the outcome of treatment include the hair growth cycle, skin color, hair color and density, and the quality of the individual hairs. TableIV shows factors that may influence photo epilation outcome. Because the duration of the hair cycle differs for different body sites, repeat treatments are usually done. Asa general rule, 6 to 10 laser sessions are required during the first year to achieve long-term epilation. With most laser systems, a single treatment can reduce hair by10–40%; three treatments by 30–70%; and repeated treatments as much as 90%. These results are maintained at post-treatment follow-up for as long as 12months. Wendy and Geronemus reported a lower level of hair regrowth after three laser treatments on the face compared with the back, shoulders and arms.62Basedon the duration of cycle length, hairs on the head havea relatively short telogen phase (6–12 weeks). Thus, a1-month interval between treatments is a sufficient time elapse for progression to the anagen phase. On the trunk, a 2-month interval is more appropriate.
- Spot size
- Pulse width
- Skin cooling system
- Fitzpatrick skin type I–III
- Fitzpatrick skin type IV–VI
- Hair thickness
- Hair color
- Follicle depth
- Anagen/telogen follicles ratio
- Hair anatomical location
- Cushing syndrome
- Polycystic ovarian disease
- Hormonal medications
- Testosterone and estradiol
- Growth factors (IGF-1)
- Photosensitive medications
- Plucking, waxing
- Sun tanning
With the proliferation of devices targeting hair and unsubstantiated claims by manufacturers, significant confusion exists in this field. Although an ever-increasing number of published studies have confirmed the long-term efficacy of laser and light-based treatments, the technology still has limits and risks. Most studies on laser hair removal are uncontrolled and have included fewer than 50 patients; none have been blinded, and all have used a variety of treatment protocols, equipment, skin types and hair colors. In addition, none of the presently utilized lasers have been proven to destroy hair permanently and long-term results are still lacking. Because lasers and light-based systems were rushed onto the market without a full understanding of their capabilities and limitations, it is vital that researchers, practitioners and consumers continue to make their experience known to the public. Current data on laser and light-based hair removal are limited by the short duration for which this technology has been practiced. More long-term studies with state-of-the-art laser hair removal technology are still needed to elucidate the optimal parameters clinically appropriate for safe and effective results in all skin and hair types/colors.
How bad does laser hair removal hurt?
Is it painful? Individuals who have undergone this hair removal procedure found it to cause a sensation similar to having a mild rubber band snap on the surface of the skin.
How many sessions do you need for permanent hair removal?
How Many Sessions do you Need for Permanent Hair Removal? Generally, 6 to 8 treatments are enough to get smooth, hairless skin with Laser Hair Removal. But this may vary from person to person based on the number, color, and texture of hair.
Is laser hair removal safe?
Laser hair removal in Dubai is the safest and probably the least painful procedure. It does not have any potential side effects as long as you are following your doctor’s pre- and post-procedural instructions carefully.
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