26 Hair Reduction with Lasers
Since the first FDA-approved laser hair reduction (LHR) device was introduced in 1995, LHR has become one of the most commonly performed cosmetic procedures with over 1 million treatments annually, according to statistics from the American Society for Aesthetic Plastic Surgery.1 Much of the popularity surrounding LHR can be attributed to its efficacy and excellent safety profile, with minimal discomfort and downtime.2
Unwanted hair growth affects both men and women, although the sites of concern and causes may vary. For men, body areas typically sought for treatment are the chest, back, shoulder, neck and ears, whereas for women, the face, chest, axilla, bikini line, and legs are usual areas of concern. Moreover, some individuals may choose to remove undesired hair for cosmetic, psychosocial, or cultural reasons; others may suffer from hirsutism due to medical conditions. In either case, undesired hair growth, if left untreated, can lead to significant distress for affected individuals and negatively influence self-image and self-esteem.
This chapter provides a basic foundation in laser principles as they relate to hair removal and a practical approach to the treatment of unwanted hair.
Laser hair removal is based on the principle of selective photothermolysis, which is the conversion of laser energy to heat, to selectively destroy hair follicles without damaging the surrounding skin tissues. To achieve this effect, laser energy is first absorbed by melanin, the target chromophore in hair. The energy absorbed by melanin is then converted into heat, which subsequently damages the hair growth structures. The surrounding skin, which minimally absorbs energy, remains unaffected.3,4
Several device parameters affect the safety and efficacy of LHR. These parameters include wavelength, fluence, pulse duration, and spot size (see Laser Parameters in Chapter 19, Aesthetic Principles and Consultation).
To target the hair follicle, wavelength selection should be specific for melanin, which preferentially absorbs laser energy between 650 and 1100 nm (Figure 26-1). These longer wavelengths also penetrate deeper into the skin to better target the hair follicles and facilitate hair removal. Four main lasers fall within this wavelength spectrum: ruby (694 nm), alexandrite (755 nm), diode (810 nm), and Nd:YAG (1064 nm) (see Figure 26-1). Whereas lasers emit single wavelengths of light energy, intense pulsed light (IPL) devices emit polychromatic light in a broad wavelength spectrum, typically between 400 and 1400 nm. Both lasers and IPL devices (collectively referred to as lasers*) used for hair reduction operate under the principle of selective photothermolysis.5
Fluence describes the amount of energy delivered per unit area (J/cm2). In general, the higher the fluence utilized, the better the hair removal results. However, higher fluences are also associated with a greater risk of complications.
Pulse duration is the amount of time the laser pulse is applied to the skin (typically in milliseconds). To confine thermal damage due to laser light energy to the desired target hair follicle, the pulse duration must be shorter than or equal to the thermal relaxation time of the follicle, typically between 10 and 100 ms (see Laser Parameters in Chapter 19 for a discussion of thermal relaxation time). Longer pulse durations are used with coarse (i.e., thick), dark hairs and for areas with high hair density. Shorter pulse durations are used for fine (i.e., thin), light hairs and areas with low hair density. Figure 26-2 summarizes the fluences and pulse durations that are used based on hair characteristics. In addition, longer pulse widths penetrate deeper into the skin and are safer for the epidermis. Therefore, darker skin types are treated with longer pulse widths and lighter skin types are treated with shorter pulse widths.
Spot size, or the diameter of the laser beam emitted (mm), correlates with energy absorption and penetration into the skin. Larger spot sizes are associated with better LHR results because larger spots have higher absorption and deeper penetration compared to small-diameter spots. Furthermore, the larger the spot size, the more body area covered per pulse, which translates to shorter treatment times.
By manipulating these various factors of wavelength, fluence, pulse width, and spot size, maximal efficacy and safety can be achieved with laser hair reduction treatments.
Proper patient selection based on an individual’s Fitzpatrick skin type, hair color, coarseness, and density is crucial for achieving successful treatments. (Refer to Chapter 19 for a review of Fitzpatrick skin types.) The ideal candidate for LHR possesses fair skin and dark, coarse hair. Fair-skin individuals (Fitzpatrick skin types I to III) have little to no epidermal melanin, which, if present, can serve as a competing target for laser energy. Thus, darker skin types (IV to VI) are at greater risk of epidermal injury with LHR treatments. Patients with Fitzpatrick skin types VI pose the greatest challenge to treatment and have the highest risk of complications, and recommendations for treatment are outside the scope of this chapter. White, light-colored (i.e., gray, blonde), and fine vellus hair lack melanin target in the hair follicle, and patients with these hair characteristics are poor candidates for LHR.
Hirsutism is excessive hair growth due to medical conditions associated with hyperandrogenic states, such as polycystic ovarian syndrome. Hypertrichosis is excessive hair growth that is not androgen dependent and, although generally idiopathic and genetic, can be due to thyroid disease, malnutrition, and medications (e.g., phenytoin, corticosteroids, and cyclosporine).
Addressing patient expectations is fundamental to ensuring patient satisfaction. First, it is important to clarify a common misconception that laser hair reduction results in complete permanent hair loss. According to the FDA, LHR is approved for permanent hair reduction, which is defined as “long-term, stable reduction in the number of hairs re-growing after a treatment regime.” Patients may experience a range of different outcomes, such as fewer, thinner, slower hair regrowth, or lighter hairs, all of which are still clinically significant and desirable.
Candidates for LHR should expect to undergo several treatments in order to achieve optimal results. Because hair growth is asynchronous and LHR is most effective for hair follicles in the anagen phase (see below), patients can expect, on average, 20% to 30% permanent hair reduction after one treatment and up to 60% to 90% reduction after completing a treatment series.6 Typically, individuals with Fitzpatrick skin types I to III require a series of six sessions, whereas skin types IV and V require eight sessions or more because treatment fluences are increased more slowly and conservatively over time with darker skin types to minimize the risk of complications.7
Common alternative treatment options to LHR include temporary hair removal methods, such as shaving, chemical depilatories, waxing, and tweezing. Currently, the only other FDA-approved method of permanent hair reduction is electrolysis, which utilizes a high-frequency electric current, via a fine-wire electrode, to destroy the hair follicle. Electrolysis is most effective for treating finer hair and may be used for nonpigmented hair including white, blonde, and gray hair. However, electrolysis is associated with more pain and longer treatment times than LHR.
Products Currently Available
A wide selection of hair removal lasers and IPL devices are available and vary by their emitted wavelengths, peak fluences, pulse durations, spot size, and cooling methods (see the Resources section at the end of the chapter for a list of suppliers).
Ruby lasers (694 nm) were one of the first lasers used for hair reduction. Although this wavelength is effective for hair reduction, it has a significant risk of complications given the high melanin absorption with this wavelength and short device pulse widths; therefore, it is not in general use today.
Alexandrite lasers (755 nm) for hair reduction are commonly used for lighter skin types (I through III).8 Relative to ruby lasers, this wavelength is safer, because it is less strongly absorbed by melanin and penetrates deeper into the epidermis. However, it is still a shorter wavelength than others used for LHR and complications such as postinflammatory hyperpigmentation can occur with darker skin types. Alexandrite devices have the advantage of being easy to use with flexible fiber-optic arms. These devices typically use cryogen spray or cool air as a means of cooling the epidermis.
Diode lasers (810 nm) are popular LHR devices that are highly effective on coarse dark hair. Darker skin types can be treated more safely than with alexandrite lasers due to the longer wavelength with deeper penetration, longer pulse widths and contact cooling of the laser tip.6 These devices also have the advantage of not having disposable parts and are small enough to sit on a tabletop.
Neodymium-doped yttrium aluminum garnet or Nd:YAG lasers (1064 nm) can be used for LHR in all skin types and are the safest devices for darker skin types (V and VI). This long wavelength is deeply penetrating, which aids in hair reduction. It has relatively poor melanin absorption and, while this protects the skin from epidermal injury, reduced melanin absorption is a disadvantage for LHR treatments. This can be overcome with the use of high fluences, coupled with intense epidermal cooling, to adequately damage hair growth structures.9
Q-switched Nd:YAG lasers, previously thought to provide only for temporary hair reduction, have recently been found to achieve permanent reduction of fine dark hair.10 The short pulse widths of these lasers (in the nanosecond range) cause mechanical oscillation of the target, also known as photoacoustic vibration. Damage to the hair follicle results from both photothermolysis and photoacoustic vibration. These lasers are most useful for the treatment of fine dark hairs, particularly on the face, and can be used with all skin types.
Intense pulsed light devices emit noncoherent, multiwavelength light ranging from 400 to 1200 nm. Cutoff filters are used to eliminate short wavelengths and allow for peaks of emission at certain desired wavelengths. For example, IPLs used for hair reduction will often use a filter that cuts off all wavelengths below 590 nm and allows for a wavelength peak between 600 and 800 nm. In this way, IPL devices can target the melanin chromophore and penetrate deeply into the skin.11 IPL devices have either single or multipulse modes (see Chapter 19). One head-to-head study showed similar clinical efficacy in hair reduction with diode, alexandrite, and IPL devices.12 Some devices are now available that combine IPL and 1064 nm to allow for treatment of a wide spectrum of skin types and hair characteristics.
Electro-optical synergy (ELOS) devices utilize radio-frequency (RF) and optical (laser or IPL light) energy together. The electrical RF energy heats the hair bulb and bulge, and the optical energy heats the hair shaft. One disadvantage of this device is that RF tends to be a more painful method of delivering energy to the skin.
In summary, different laser wavelengths are best suited to different skin types and different hair characteristics. The preceding discussion provides general guidelines; however, the indications for treatment of different skin types are device specific and are determined by the FDA. For example, most IPL devices are approved for LHR in skin types I through IV, however, certain IPL manufacturers’ devices are also approved for treatment of skin type V. The specifics about a particular device should be sought from the laser manufacturer.
General Laser Contraindications
The following contraindications apply to LHR and the laser treatments discussed in Chapters 27 through 30:
Advantages of LHR
Disadvantages of LHR
Hair follicles are composed of the bulb (which consists of the matrix and dermal papilla), outer root sheath, bulge, and hair shaft (Figure 26-3). The hair matrix depth in the skin ranges from 2 to 7 mm, depending on the body location, and the hair bulge is approximately 1.5 mm. Hair growth occurs in three phases with distinct changes below the skin in the hair bulb: (1) anagen, the active growth phase during which the hair bulb is most darkly pigmented; (2) catagen, the regression phase when cell division ceases and the follicle begins to involute; and (3) telogen, the resting phase during which the hair bulb is minimally pigmented (Figure 26-4). The hair shaft visible on the surface of the skin, however, is indistinguishable throughout these phases.