13 Hair Removal
Laser hair removal is based on the concept of selective photothermolysis.
Melanin is the hair follicle′s only endogenous chromophore and is the target for laser hair removal.
The use of lasers with longer wavelengths, such as the Nd:YAG, has allowed patients with darker skin to undergo treatment for unwanted hair.
Adjustment of other laser parameters, such as pulse width, also aids in the reduction of complications and optimizes results.
Future advancements are needed in the treatment of hair lacking melanin, such as blond or gray hair.
The desire to remove unwanted hair is common in both women and men. Temporary methods such as waxing, shaving, and bleaching continue to be used for this purpose, but patients and practitioners have for years sought a more permanent solution. Until the mid-1990s, the only reliable, long-lasting method to remove hair was electrolysis, which, unfortunately, is poorly tolerated by patients and can be expected to achieve only a 15 to 50% permanent reduction in hair.1,2 Since then, lasers (light amplification by stimulated emission of radiation) have been used for hair reduction, and laser hair removal has taken over as a popular, effective way to achieve a permanent reduction in hair.
Background: Basic Science of Procedure
A reduction in hair was noted with the first lasers and was achieved by epidermal injury.1 In 1996, Grossman first reported the removal of hair using the ruby laser.3 There were no significant advances in hair reduction until the method in which lasers worked (selective thermolysis) was understood.
Selective photothermolysis is the selective destruction (or absorption) of a target chromophore using a brief pulse of radiation with preservation of surrounding structures using the appropriate wavelength, fluence, pulse duration, and energy.4 The chromophore targeted in laser hair reduction is melanin, and the laser parameters used vary according to the specific laser and patient characteristics, including hair color and patient skin type. Various studies over the years have shown that selective removal of hair is possible using a variety of laser systems and intense pulsed light (IPL).1
Today, the primary wavelengths used for hair removal range from 755 to 1,100 nm, which absorb melanin well.5 These correspond to the alexandrite, diode, and neodymium: yttrium-aluminum-garnet (Nd:YAG) lasers. The IPL system can also be used for hair removal but is not a laser. Instead, IPL systems emit a spectrum of light that can be used to direct energy to specific targets, such as melanin, by adding filters.2
As noted previously, laser hair removal is based on the concept of selective photothermolysis. Melanin is the hair follicle′s only endogenous chromophore and is found in the bulb and bulge of the hair follicle.1,6 Absorption of the heat from the laser by the melanocyte damages, and, ideally, destroys, the follicle.7 The main competing chromophores are melanin within the superficial epidermis and hemoglobin found within superficial capillaries.1 Being able to target primarily the melanin within the hair follicle without affecting competing chromophores is one of the main struggles as well as the focus for research in this field.
To fully understand the concept of laser hair removal, a review of the normal hair cycle and hair biology is warranted. Hair follicles have a cyclical growth pattern, and the duration of each cycle varies with anatomical subsite.2 The first cycle is the anagen, or growth, phase; the second stage is called the catagen phase and is the time in which apoptosis occurs; this is followed by the final, quiescent, telogen phase, during which the hair falls out.
It is the anagen phase of the hair cycle during which laser treatments are believed to be the most effective. The anagen phase of hair follicle growth typically lasts for 2 months to 1 year for hair follicles in the face but varies due to factors such as body site, age, sex, hormonal influences, and genetics.2 In spite of this variation, between 80 and 85% of hair follicles are in the anagen phase of the hair cycle at any given time.2 Repeated laser treatments are performed every 4 to 12 weeks, with the thought that it is during this time period that there is a burst of rapid hair regrowth.2
The depth of each hair follicle varies between 2 and 7 mm from the skin surface, depending on the specific anatomical subunit within the body.2 Although it is not entirely understood which portion of the hair follicle is responsible for hair growth, it is thought that the major growth center is the matrix. The follicle has an exceptional ability to regenerate and self-repair, which impedes the effectiveness of laser hair removal therapy.8 Current laser hair removal techniques attempt to permanently damage the entire follicle at an estimated depth; the specific depth chosen is based on the targeted anatomical subunit.8
During the initial consultation with any patient interested in laser hair reduction, it is important to obtain a thorough history and physical examination, as well as have an open discussion regarding the patient′s expectations as compared with the potential results. The history should include information such as whether the patient has undergone previous hair reduction treatments because it is prudent to wait 6 weeks prior to performing any additional treatment.
During the examination, the physician should note the patient′s Fitzpatrick skin type, hair color/thickness, the presence of tattoos or suspicious moles, and the possible presence of a systemic disorder, such as hirsutism (the presence of terminal, coarse hairs in females in a male-like pattern).4 If one suspects hirsutism, a referral to a specialist may be indicated prior to laser hair treatment because it is typically a sign of an underlying endocrine abnormality.4 Pre-treatment photographs of the areas to be treated are taken and can be useful tools for posttreatment comparison and evaluation of whether the treatment was successful.
Patient education is performed prior to the first treatment. It is important that patients understand that they should anticipate needing three to seven treatments to achieve the desired results. We also counsel our patients to avoid tanning or burning prior to the treatment because darker skin will decrease the effectiveness of the treatment and may increase the risk of complications, such as blistering, scarring, and hyperpigmentation.1 Finally, we also ask our patients to avoid tweezing or waxing on the day of the procedure because these processes can remove the target chromophore (melanin) at the base of the hair follicle.
Technical Aspects of Procedure
Lasers are composed of an energy source, a focusing (or gating) system, and a radiating medium. The medium determines the wavelength emitted, such as 755 nm for an alexandrite laser Video 13.1. The characteristics of the laser itself can be adjusted by changing one or more of the following parameters: fluence (amount of laser energy per unit area [joules per square centimeter]), pulse width (length of time of exposure to the skin), and spot size (surface area of skin exposed to the laser beam).9
Laser parameters can be adjusted to more selectively injure the hair follicle.1 One method is to lengthen the pulse width. When the pulse width is longer than the thermal relaxation time of the superficial melanin but shorter than that of the hair follicle, the hair follicle can be injured without damage to the skin.1
Cooling of the skin can also help to protect the skin surface during laser hair removal. In addition, skin cooling may have an added benefit of increased patient tolerance to the treatment because it has been found to help reduce pain.9 Skin cooling in combination with longer pulse widths has also allowed patients with darker skin to benefit from laser hair removal.9 Compression of the skin during treatment can also help to push blood out of the capillaries in the area to reduce the absorption by the competing chromophore, hemoglobin.
There are several lasers used for hair removal treatments. The following section reviews the specific technical aspects for the Nd:YAG laser. A brief summary of the other laser systems used to remove hair follows.
There are three main parameters that need to be set when using the Nd:YAG laser for hair reduction treatment: cooling temperature, fluence, and pulse width. Each can be adjusted to a specific patient′s needs. The common starting settings are discussed here, although there is not a fixed setting appropriate for all patients.
Performing a test spot prior to each treatment can also help to reduce the risk of complications. If any blistering, excessive swelling, or redness is noted, then another test spot should be performed with different laser parameters. Treatment should not be performed until a satisfactory test spot result is seen.1
As noted previously, pretreatment discussion with the patient about expectations, possible complications, and pretreatment care is necessary. All patients should have pretreatment photos taken for documentation, and all should give informed consent. A topical anesthetic may be applied to the treatment area 30 minutes before the procedure to decrease patient discomfort. The skin should also be washed with a gentle cleanser and thoroughly dried prior to treatment.
The cooling temperature is typically set on a separate chilling device. Zero to 15°C will usually provide for maximal patient comfort, and most treatments can be done with a cooling temperature of 15°C. A coating of colorless gel is also placed on intended treatment areas to permit better heat removal. Of note, if the fluence is increased, the cooling temperature should be decreased and vice versa.10
The fluence used is dependent on the starting surface area temperature of the skin, as well as such factors as whether or not the patient has been treated before and his or her response to treatment. In general, one may start at 65 J/cm2 and increase fluence by 10% at each subsequent treatment.
The pulse width is set from 15 to 40 msec. Keeping the pulse width shorter or equal to the thermal relaxation time of the hair follicle (~ 10 to 50 msec) helps to limit or prevent collateral thermal damage.11 The specific setting used is partially determined by the size of the hair shaft and follicle. Coarse hair typically requires a pulse width of 20 msec, whereas in those with darker skin tones, a longer pulse width is used ( Fig. 13.1a–d ). As the hair reduces in size over the course of treatments, the pulse width may also need to be reduced. We typically decrease pulse width by 5 msec at each treatment session. The Nd:YAG laser has been successfully used to remove hair in patients with darker skin types ( Fig. 13.1 ).