The hair follicle is a hormonally active structure (Fig. 4.1) that is anatomically divided into an infundibulum (hair follicle orifice to insertion of the sebaceous gland), isthmus (insertion of the sebaceous gland to the insertion of the arrector (erector) pili muscle), and inferior (insertion of the arrector pili to the base of the hair follicle) segments. The dermal papilla provides neurovascular support to the base of the follicle and helps form the hair shaft.

Figure 4.1 Hair follicle anatomy.

Reproduced from Tsao SS, Hruza GJ 2005 Laser hair removal. In: Robinson JK, Hanke CW, Sengelmann RD, Siegel DM (eds) Surgery of the Skin. Elsevier Mosby, Philadelphia, p 575-588.

Every hair follicle is controlled by a programmed cycle that is dependent on the anatomical location. The hair cycle consists of anagen, catagen, and telogen phases. Anagen is characterized by a period of active growth where the hair shaft lengthens. A catagen transition period follows in which the lower part of the hair follicle undergoes apoptosis. A resting period, telogen, then ensues, and regrowth occurs when anagen resumes. Hair regrowth (entry into another anagen cycle) is dependent on stem cells within or near the hair bulb matrix. Slow-cycling stem cells have also been found in the follicular bulge arising off the outer root sheath at the site of the arrector pili muscle attachment.

The main types of hair include lanugo, vellus, and terminal hairs. Lanugo hairs are fine hairs that cover a fetus and are shed in the neonatal period. Vellus hairs are usually non-pigmented, and have a diameter of roughly 30–50 µm. Terminal hair shafts range from 150 to 300 µm in diameter. The type of hair produced by an individual follicle is capable of change (e.g. vellus to terminal hair at puberty or terminal to vellus hair in androgenic alopecia).

The amount and type of pigment in the hair shaft determine hair color. Melanocytes produce two types of melanin: eumelanin, a brown-black pigment; and pheomelanin, a red pigment. Melanocytes are located in the upper portion of the hair bulb and outer root sheath of the infundibulum.

Definitions of what constitutes excessive or unwanted body hair depends on cultural mores, but can usually be classified as either hypertrichosis or hirsutism. Hirsutism is the abnormal growth of terminal hair in women in male-pattern (androgen-dependent) sites such as the face and chest. Hypertrichosis is excess hair growth at any body site that is not androgen dependent. Additionally, the use of grafts and flaps in skin surgery can often introduce hair to an area that causes a displeasing appearance or functional impairment.

Mechanism of LHR

The theory of selective photothermolysis enables precise targeting of pigmented hair follicles by using the melanin of the hair shaft as a chromophore. Melanin has an absorbance spectrum that matches wavelengths in the red and near-infrared (IR) portion of the electromagnetic spectrum. To achieve permanent hair removal, the biological ‘target’ is the follicular stem cells located in the bulge region and / or dermal papilla. Due to the slight spatial separation of the chromophore and desired target, an extended theory of selective photothermolysis was proposed that requires diffusion of heat from the chromophore to the desired target for destruction. This requires a laser pulse duration that is longer in duration than if the actual chromophore and desired target are identical. Temporary LHR can result when the follicular stem cells are not completely destroyed, primarily through induction of a catagen-like state in pigmented hair follicles. Temporary LHR is much easier to achieve than permanent removal when using lower fluences. Long-term hair removal depends on hair color, skin color, and tolerated fluence. Roughly 15–30% long-term hair loss may be observed with each treatment when optimal treatment parameters are used (Fig. 4.2). A list of laser and light devices that are currently commercially available for hair removal is given in Table 4.1.

Figure 4.2 Laser hair removal is safe and effective. (A) The upper cutaneous lip of a hirsute female. (B) Appearance of same subject following only three treatments with a long-pulsed 755 nm alexandrite laser used with a 12 mm spot size, 16 J/cm², 3 ms pulse duration and DCD setting of 30/30/0. (C) Axilla of an adult female. (D) Following four treatments with a long-pulsed diode laser with a large spot size and vacuum-assisted suction. The fluence used was 12 J/cm² and the pulse duration was 60 ms. Both of the above subjects achieved excellent hair reduction and further benefit would likely be attained with additional treatments.

Table 4.1 Commercially available lasers and light sources for hair removal^*

Key factors in optimizing treatment

LHR has revolutionized the ability to eliminate unwanted hair temporarily and permanently in many individuals of all skin colors. Proper patient selection, preoperative preparation, informed consent, understanding of the principles of laser safety, and laser and light source selection are key to the success of laser treatment. An understanding of hair anatomy, growth and physiology, together with a thorough understanding of laser–tissue interaction, in particular within the context of choosing optimal laser parameters for effective LHR, should be acquired before using lasers for hair removal.

Patient selection

A focused medical history, physical examination, and informed consent, including setting realistic expectations and potentials risks, should be performed prior to any laser treatment (Box 4.1). Patients with evidence of endocrine or menstrual dysfunction should be appropriately worked up. Similarly, patients with an explosive onset of hypertrichosis should be evaluated for paraneoplastic etiologies. Treatment of a pregnant woman for non-urgent conditions is discouraged by the authors, although there is no evidence suggesting a potential risk to pregnant women undergoing LHR. The past medical history should be reviewed to identify patients with photosensitive conditions, such as autoimmune connective tissue disorders, or disorders prone to the Koebner phenomenon. A history of recurrent cutaneous infections at or in the vicinity of the treatment area might warrant the use of prophylactic medications. Any past history of keloid or hypertrophic scar formation should be elicited as well. Previous hair removal methods, including past laser treatments, should be reviewed. Any methods of hair shaft epilation (e.g. waxing or tweezing) that entirely remove the target chromophore render LHR less effective for at least 2 weeks. Although there is little evidence for the time frame a patient must wait after complete epilation of the hair shaft and laser treatment, we recommend a minimum of 6 weeks. Shaving and depilatory creams can be used up to the day of laser treatment as they do not remove the entire hair shaft.

Box 4.1

Pertinent medical history for laser / pulsed light hair removal

Presence of conditions that may cause hypertrichosis:

Hormonal

Familial

Drugs (i.e. corticosteroids, hormones, immunosuppressives, self or spousal use of minoxidil)

Tumor

History of local or recurrent skin infection

History of herpes simplex, especially perioral

History of herpes genitalis, important when treating the pubic or bikini area

History of keloids / hypertrophic scarring

History of koebnerizing skin disorders such as vitiligo and psoriasis

Previous treatment modalities – method, frequency, and date of last treatment, as well as response

Recent suntan or exposure to tanning or light cabinet

Onset of hair regrowth (recent)

Tattoos or nevi present

Patient’s expectations

Patient’s hobbies or habits which might interfere with treatment

Present medications:

– Photosensitizing medications

– Isotretinoin intake within the past month

Case Study 1

A 27-year-old Hispanic female with Fitzpatrick skin type IV presents to you for hair removal on the ‘beard area’. She has been treated five times with a diode laser over the course of 2 years at a local spa and notes only a minimal reduction of hair. On review of systems, you discover that the patient has had a history of irregular menses and periodically flaring acne. She does not see a gynecologist.

While it appears that the patient is responding poorly to laser treatment, a thorough history reveals that the patient has clinical and historical evidence of hormonal dysfunction. This imbalance may be driving the conversion of vellus hair to terminal hair and can make it appear that laser hair removal treatments are ineffective, when in reality the patient is responding to treatment but is creating new hair follicles.

Pearl 1

It is imperative to counsel the patient not to partake in any epilation activities that remove the entire hair shaft. Shaving or using a chemical depilatory prior to treatment is acceptable but waxing or plucking will be counteractive to the laser treatments. A 2-week interval after such procedures is recommended for improved efficacy.

A medication history should be obtained. Gold intake is a contraindication for laser therapy with Q-switched lasers as there is a risk of the complication of chyrsiasis. The use of any photosensitizing medications or over-the-counter supplements should be held before treatment. Although there is a lack of convincing data, a washout period for patients on isotretinoin may be considered prior to laser treatment. Topical retinoids used in the treatment area should be discontinued 1 to 2 days prior to treatment. Finally, the patient’s reaction to unprotected sun exposure (Fitzpatrick skin phototype) should be elicited as part of the history.

The physical exam should corroborate the patient’s Fitzpatrick skin phototype. This will help determine which lasers and light sources are safe to use for that patient (see Table 4.1) because epidermal melanin in darkly pigmented patients competes with the melanin within hair follicles as a chromophore. Importantly, every patient should always be evaluated for the presence of a tan and, if present, laser treatment should be delayed or the treatment parameters appropriately adjusted until the tan has faded. Finally, the patient’s hair color should be noted as the chromophore for LHR is melanin. Black and brown terminal hairs typically contain sufficient amount of melanin to serve as a chromophore for LHR. In contrast the lack of melanin, paucity of melanin or presence of eumelanin in the hair follicle, which clinically correlates with white, gray, or red / blonde hair respectively, is predictive of a poor response to laser hair removal (Fig. 4.3). For patients with little to no melanin in their hair follicles, attempts have been made to use exogenous chromophores that can be topically delivered to the hair follicles, thereby making the removal of white, gray, red, and blonde hair hypothetically possible. This concept was first demonstrated with a topical carbon solution dissolved in mineral oil. However, we have noticed very little long-term hair reduction efficacy of topical chromophores in our experience. The coarseness and density of hair are also important to note as these factors will influence parameter settings (see below).

Figure 4.3 Effective laser hair removal can be obtained for dark, pigmented hairs, but not for white hairs: (A) before, and (B) after treatment.

Pearl 2

Treatment on tanned patients should be delayed until the tan fades. Risk of pigmentary alteration is significantly higher in these patients.

Pearl 3

Patients with white, gray, or blonde hair are currently not appropriate candidates for laser hair removal. Other methods of epilation should be encouraged.

Informed consent

Informed consent requires a review of the potential risks of LHR, which include, but are not limited to, temporary and permanent hypo / hyperpigmentation, blister formation, scar formation, ulceration, hive-like response, bruising, infection, acne flare, and folliculitis. For those patients with Fitzpatrick skin type IV or greater or of Mediterranean, Middle Eastern, Asian or South Asian descent, the low risk of paradoxical hypertrichosis (conversion of vellus hairs to thicker, more obvious terminal hairs), especially when treating the lateral face and jaw, should be reviewed. Patients should be counseled that permanent and complete hair removal is not likely but that, with multiple treatments, significant long-term reduction can be achieved. Hirsute women with hormonal abnormalities such as polycystic ovarian syndrome may require continued maintenance therapy and should be advised of this possibility. Procedural pain is expected with LHR but can be minimized with topical anesthetics. Erythema and edema are also expected with treatment and may last up to 1 week. Patients should be aware of the need for strict sun avoidance for a minimum of 6 weeks before and after each treatment.

Case Study 2

A 32-year old Egyptian female presents for laser hair removal of the lateral preauricular face. On physical exam, she is a Fitzpatrick skin type V with fine, dark vellus hairs in the area of interest.

This patient is a challenge for a variety of reasons (dark skin type, caliber of hair to be treated). Importantly, it is critical for the laser surgeon to also review the rare risk of paradoxical hypertrichosis (see above). Paradoxical hypertrichosis is a poorly understood phenomenon in which laser stimulates hair growth or a change in hair type from vellus to terminal hairs. This produces an obvious worsening in the appearance of the affected hairs in a cosmetically sensitive area, i.e. the face. Although challenging, these increased hairs can be treated with further hair removal but they may be more resistant to therapy.

Preoperative preparation and laser safety

The need for topical anesthesia is variable among patients and anatomic sites. Various topical anesthetics including lidocaine, lidocaine / prilocaine, and other amide / ester anesthetic combinations can be used to diminish the procedural discomfort, and should be applied 30 minutes to 1 hour before treatment under occlusion. Care should be taken when using lidocaine or prilocaine to apply these medications to a limited area to diminish the risk of lidocaine toxicity or methemoglobulinemia, respectively. Deaths have resulted from lidocaine toxicity resulting from occlusion of the back as well as lower extremities with topical lidocaine. Likewise, systemic toxicity can occur with the use of any topical anesthetic in large amounts.

Pearl 4

Occlusion increases the absorption of topical medications by at least an order of magnitude. Lidocaine is a cardiotoxic medication and prilocaine can convert hemoglobin into methemoglobulin. Large areas such as the back or legs should have topical anesthesia applied with caution.

Patients should be placed in a room with a treatment chair that makes the desired treatment area easily accessible. The room should be adequately cooled to keep the laser device from overheating and be free of any hanging mirrors or uncovered windows. A fire extinguisher should be readily available. If possible, supplemental oxygen should be turned off when performing laser treatments. Having a vacuum device on hand during treatment can minimize the plume and unpleasant odor created by each laser pulse. Because the retina contains melanin that can be damaged by wavelengths in the red and near-infrared range, proper eye protection is absolutely critical for both the patient and laser surgeon. Goggles are not interchangeable between lasers or IPL devices of different wavelengths. Furthermore, because of the risk of retinal damage from the deeply penetrating wavelengths used for LHR, one should never treat a patient for LHR within the bony orbit.

Case Study 3

A 35-year old female with Fitzpatrick skin type II and jet-black hair presents to you for laser hair removal. During the consultation, she states her primary concern is that she would like to have her eyebrows shaped permanently. She is inconvenienced by her current regimen of waxing every several weeks.

The patient is an ideal candidate for LHR with her fair skin and dark hair. Almost any hair removal laser would be appropriate for use. The issue of concern in this case is the location of treatment. Caution must be taken when treating near the eye, as there is a risk of damage to retinal pigment.

Device variables

Wavelength

The chromophore for laser hair removal is melanin. Within the hair follicle, melanin is principally located within the hair shaft, although the outer root sheath and matrix area also contain melanin. Melanin is capable of functioning as a chromophore for wavelengths in the red and near-IR portion of the electromagnetic spectrum, and can be targeted by ruby, alexandrite, diode and Nd : YAG lasers, as well as IPL devices.

The long-pulsed ruby laser (694 nm) was the first device used to selectively target hair follicles, resulting in long-term hair loss. The long-pulsed ruby laser can be safely used in Fitzpatrick skin phototypes I–III. Table 4.1 lists the long-pulsed ruby lasers that are commercially available.

The long-pulsed alexandrite (755 nm) laser has been shown to be effective for long-term hair removal in multiple studies. The long-pulsed alexandrite laser can be safely used in Fitzpatrick skin phototypes I–IV, although some experts limit the use of the long-pulsed alexandrite laser to Fitzpatrick skin phototypes I–III. A few studies have demonstrated the safety of the long-pulsed alexandrite laser in a large cohort of patients with Fitzpatrick skin phototypes IV–VI. Combination treatment of alexandrite and Nd : YAG lasers provides no added benefit over the alexandrite laser alone. The commercially available long-pulsed alexandrite devices are summarized in Table 4.1.

The long-pulsed diode (800–810 nm) laser (LPDL) has also been extensively used for LHR. The diode laser can be safely used in patients with Fitzpatrick skin phototypes I–V and has good long-term efficacy for LHR.

The long-pulsed Nd : YAG laser has been thought to offer the best combination of safety and efficacy for Fitzpatrick skin phototype VI patients. Long-term hair reduction with 18-month follow-up showed 73.6% clearance following four treatments at 2-month intervals.

IPL is composed of polychromatic, non-coherent light ranging from 400 to 1200 nm. Various filters can be used to target particular chromophores, including melanin. Long-term (>1 year) hair removal has not been convincingly demonstrated to date. Various reports have demonstrated short-term efficacy. One study of patients treated with a single IPL session reported 75% hair removal 1 year after treatment. Two studies providing a head-to-head comparison of IPL versus either the long-pulsed alexandrite laser or Nd : YAG laser both found the IPL to be inferior to laser devices for hair removal. In contrast, a study of hirsute women, some with a diagnosis of polycystic ovarian syndrome, who underwent a split-face treatment with six IPL or LDPL show statistically equivalent reductions in hair counts at 1 (77% versus 68%, respectively), 3 (53% versus 60%, respectively) and 6 months (40% versus 34%, respectively) after the final treatment.

Pearl 5

One should always evaluate the patient’s Fitzpatrick skin type when evaluating a patient for LHR. Darker skin types require longer wavelengths, which pose a lower risk of side effects from the absorption of energy by epidermal melanin.

Fluence

Fluence is defined as the amount of energy delivered per unit area and is expressed as J/cm². Higher fluences have been correlated with greater permanent hair removal, but are also more likely to cause untoward side effects. Recommended treatment fluences are often provided with each individual laser device for non-experienced operators. However, a more appropriate method of determining the optimal treatment fluence for a given patient is to evaluate for the desired clinical end point of perifollicular erythema and edema seen within a few minutes of treatment (Fig. 4.4). The highest possible tolerated fluence that yields this end point without any adverse effects is the best fluence for treatment. Fluences that cause epidermal disruption are too high and should be reduced.

Figure 4.4 Formation of perifollicular eythema and edema immediately after laser treatment.

Pearl 6

When treating a patient for LHR for the first time, it may be prudent to try several test spots at varying fluences to determine the optimal settings. The highest tolerable fluence without epidermal damage will yield the greatest amount of hair clearance per treatment.

Pulse duration

Pulse duration is defined as the duration in seconds of laser exposure. The theory of selective photothermolysis enables the laser surgeon to select an optimal pulse duration based on the thermal relaxation time (TRT). Terminal hairs are about 300 µm in diameter, and thus the calculated TRT of a terminal hair follicle is about 100 ms. However, unlike many other laser applications, the hair follicle is distinct in that there is a spatial separation of the chromophore (melanin) within the hair shaft and the biological ‘target’ stem cells in the bulge and bulb areas of the follicle. The expanded theory of selective photothermolysis takes this spatial separation into account and proposes a thermal damage time (TDT), which is longer than the TRT. Shorter pulse widths are also capable of removing hair, and it is unclear which is more effective in producing permanent hair removal. Longer pulse widths are likely more selective for melanin within the hair follicle and can minimize epidermal damage as the pulse widths are greater than the TRT of the melanosomes in epidermal keratinocytes and melanocytes.

Pearl 7

When treating darker Fitzpatrick skin types, a longer pulse duration is preferred as the pulse duration exceeds the thermal relaxation time of the epidermal melanin, and minimizes the risk of epidermal damage.

Spot size

The spot size is the diameter in millimeters of the laser beam. As photons within a laser beam penetrate the dermis they are scattered by collagen fibers, and those that are scattered outside the area of the laser beam are essentially wasted. Photons are more likely to be scattered outside of the beam area for smaller spot sizes, whereas in a larger spot size the photons are likely to remain within the beam area following scatter. A double-blind, randomized controlled trial of a long-pulsed alexandrite laser for LHR of the axillary region comparing 18 and 12 mm spot sizes at otherwise identical treatment parameters showed a 10% greater reduction in hair counts with the larger spot size. Recently, a prospective study using a LDPL with a large 22 × 35 mm handpiece at low fluences and no skin cooling was shown to have similar long-term hair removal efficacy to published studies of LPDLs with smaller spot sizes using higher fluences and skin cooling. Thus, larger spot sizes are preferable to smaller spot sizes.

Pearl 8

Using the largest possible spot size allows for optimal penetration and minimizes the number of pulses it takes to cover a treatment area, thereby translating to faster treatment courses.

Skin cooling

The presence of epidermal melanin, particularly in darker skin types, presents a competing chromophore to hair follicle melanin, which can be damaged during LHR (Fig. 4.5). Cooling of the skin surface is used to minimize epidermal damage as well as pain, while permitting treatment with higher fluences. All of the skin-cooling methods function by acting as a heat sink and removing heat from the skin surface. The least effective type of cooling is the use of an aqueous cold gel, which passively extracts heats from the skin and then is not capable of further skin cooling. Alternatively, cooling with forced chilled air can provide cooling to the skin before, during, and after a laser pulse. Currently, most of the available LHR devices have a built-in skin cooling system, which consists of either contact cooling or dynamic cooling with a cryogen spray. Contact cooling, usually with a sapphire tip, provides skin cooling just before and during a laser pulse. It is most useful for treatments with longer pulse durations (>10 ms). Dynamic cooling with cryogen liquid spray pre-cools the skin with a millisecond spray of cryogen just before the laser pulse. A second spray can be delivered just after the laser pulse for post-cooling, but parallel cooling during the laser pulse is not possible as the cryogen spray interferes with the laser beam. Dynamic cooling is best suited for use with pulse durations shorter than 5 ms.

Figure 4.5 Inadequate contact cooling resulting in postinflammatory hypopigmentation in a patient with type V skin.

Photograph courtesy of Nathan Uebelhoer.

Pearl 9

Skin cooling is beneficial for minimizing epidermal damage and treatment-associated pain. However, cooling can be overdone and result in pigmentary alterations, particularly with cryogen liquid spray.

Post-procedure care

It is expected for the patient to have perifollicular erythema and edema in the treatment area following LHR. This generally persists for 2 days but can last for up to 1 week. Ice and application of a topical corticosteroid can be used to shorten the duration of these undesired clinical findings. Patients will often find that a single treatment of LHR with shorter pulse durations results in nearly total epilation of the hair follicles in the treatment area. It is important to counsel the patient that a majority of these hairs will likely regrow, and this isn’t considered a treatment failure. Generally, only about 15% of hairs are permanently removed with each laser treatment. On the other hand, LHR treatments with longer pulse durations may leave behind many hairs that appear to ‘grow’ following treatment. It is important to reassure the patient that these ‘growing’ hairs are dislodged from the hair follicle and require 1–2 weeks to be completely shed. Nearly any method of epilation can be used to hasten their removal.

The importance of strict sun precaution following LHR treatments cannot be overemphasized. This can be achieved by the use of topical sunscreens, ultraviolet light impermeable garments, and, most importantly, sun avoidance.

Pearl 10

Beyond SPF30, higher SPF values do not necessarily correlate with increased protection from the sun. The SPF value of a product only reflects its protection from UVB rays. It is far more important that the product contain broad-spectrum protection, including UVA rays.

Long-term efficacy

Evidence of permanent hair removal was evident as early as the seminal hair removal trial from the Wellman Center involving a single treatment with the normal mode ruby laser. Seven of the 13 original subjects were evaluated at 2-year follow-up. Of the 7 subjects, 4 had evidence of persistent permanent hair reduction at 2-year follow-up, whereas 3 subjects experienced complete regrowth. Follow-up of 18 out of the 50 original study subjects treated with a LPDL showed a 25–33% and 36–46% hair reduction at a mean follow-up of 20 months after one or two treatments (9 mm spot size, pulse duration of 5–20 ms, fluences of 15–40 J/cm², single or triple pulsed) respectively. A head-to-head trial comparing a LPDL to a long-pulsed alexandrite laser found a 49–94% hair reduction at 1-year follow-up after four treatments (9 mm spot size, pulse duration of 20 ms, fluences of 12–40 J/cm²) with the LPDL in 15 subjects. Similar results were achieved with the alexandrite laser used in this study. Fifteen of 20 subjects with Fitzpatrick skin phototypes III–IV treated with a long-pulsed alexandrite laser (12 and 18 mm spot size, 3 ms pulse duration and fluences of 20 or 40 J/cm²) or a long-pulsed Nd : YAG laser (12 mm spot size, 3 ms pulse duration and fluence of 40 J/cm²) for four sessions at 8-week intervals showed 76–84% and 74% hair reduction 18 months after the last treatment respectively. Another head-to-head trial of a high fluence LPDL (9 mm spot size, pulse duration of 30 ms, fluences of 20–50 J/cm²) versus a low fluence LPDL (12 × 10 mm spot size, pulse duration of 20 ms, fluences of 5–10 J/cm²) in 22 subjects showed similar, 94% and 90% hair reduction at 18 month follow-up following five treatments spaced 6–8 weeks apart, respectively. Finally, the authors recently reported statistically significant hair clearance, 54% and 42%, at 6- and 15-month follow-up visits following three monthly treatments using a LPDL with a large handpiece in the largest prospective trial to date. Remaining hairs were found to also grow back less thick and lighter.

Complications

The most common complications of LHR are epidermal damage (Fig. 4.6) and pigmentary alterations, including hyper- and hypopigmentation (Fig. 4.7). This may result from selecting a non-optimal wavelength, pulse duration or fluence, using inadequate epidermal cooling or treating a tanned patient (Fig. 4.8). Pigmentary alterations may also occur even when optimal treatment parameters are used. These changes are often transient and improve with time, although permanent hypopigmentation can occur (Fig. 4.7B). Zones of untreated hairs can result from a lack of overlapping between laser pulses (Fig. 4.9). Scarring is an exceedingly rare complication but can occur when excessive fluences and / or pulse stacking are used.

Figure 4.6 Epidermal damage with focal crusting resulting from excessive laser fluence.

Figure 4.7 Example of laser hair removal induced hyperpigmentation (A) and permanent hypopigmentation (B).

Figure 4.8 Treatment of recently tanned skin resulted in development of hypopigmentation.

Figure 4.9 Zones of untreated skin resulting from lack of appropriate overlapping.

Treatment of the lateral cheeks and chin area, or less commonly other areas, may result in the induction of terminal hairs, a phenomenon known as paradoxical hypertrichosis (Fig. 4.10). This has been reported to occur more commonly in females of Mediterranean, Middle Eastern, Asian and South Asian descent. The exact mechanism remains uncharacterized but it is thought that subtherapeutic laser fluences may lead to the stimulation of hair growth.

Figure 4.10 Paradoxical hypertrichosis. Conversion of fine, vellus-like hairs (A) to terminal dark hairs (B) after a single laser hair removal treatment.

Caution should be exercised to avoid treatment of tattoos and nevi, particularly atypical nevi.

Conclusion

Future directions

Electro-optical synergy (ELOS) technology combines electrical (conducted radiofrequency) and optical (laser / light) energies. A handful of devices based on this technology have been produced (see Table 4.1). The theory behind ELOS is based on the optical component (laser or IPL) heating the hair shaft, which then is thought to concentrate the bipolar radiofrequency (RF) energy to the surrounding hair follicle. Based on this combination, lower fluences are needed for the optical component, thereby suggesting it might be well tolerated in all Fitzpatrick skin phototypes, and potentially effective in the removal of white and poorly pigmented hair. A study of 40 patients (Fitzpatrick skin phenotypes II–V) with varied facial and non-facial hair colors were treated with combined IPL / RF ELOS technology. An average clearance of 75% was observed at 18 months following four treatments. No significant adverse sequelae were noted and there were no treatment differences between patients of varying skin types or hair color. Pre-treatment with aminolevulinic acid (ALA) prior to use of a combined IPL and radiofrequency device has been shown to further augment the removal of terminal white hairs.

In conclusion, hair removal has made a dramatic shift from an art to science based on the theory of selective photothermolysis. Since the first reports of selective hair removal in 1996 by Anderson and colleagues, there has been a tremendous explosion in the number of devices used for LHR, making LHR the most commonly requested cosmetic procedure in the world. This chapter provides the reader with the fundamentals of hair follicle anatomy and physiology, points for patient selection and preoperative preparation, principles of laser safety, an introduction to the various laser / light devices and a discussion of laser–tissue interactions that are vital to optimizing treatment efficacy while minimizing complications and side effects.

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Laser hair removal

Introduction

Basic hair biology