Laser Principles

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

FIGURE 26-1 Chromophore absorption spectrum and common hair reduction lasers.

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.

FIGURE 26-2 Hair characteristics and laser parameters.

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.

Patient Selection

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.

Indications

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).

Patient Expectations

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

Alternative Therapies

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.

Contraindications

Advantages of LHR

Disadvantages of LHR

Anatomy

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.

FIGURE 26-3 Hair anatomy.

FIGURE 26-4 Three phases of hair growth: (A) anagen, (B) catagen, and (C) telogen.

(From Robinson J, Hanke W, Sengelmann R, Siegel D. Surgery of the Skin: Procedural Dermatology, 2nd ed. Philadelphia: Mosby; 2010.)

Hair growth is initiated by epithelial stem cells located in the “bulge,” a protrusion near the attachment of the arrector pili muscle, and also occurs from the rapidly dividing matrix cells of the hair bulb. Hairs are most susceptible to laser treatment during the early anagen phase when the melanin content of the matrix is greatest. The percentage of hairs in anagen varies for different parts of the body (Table 26-1), and those areas with the greatest percentage in anagen, such as the scalp, respond most rapidly to laser treatments. The duration of the telogen phase serves as a rough guideline for the interval between treatments. For example, the lower legs, which have a long telogen phase, require intervals of approximately 3 months between treatments, whereas the upper lip, which has a short telogen phase, requires approximately 1 month between treatments (Table 26-1).

TABLE 26-1 Percentage of Hairs in Anagen and Duration of Telogen Phase for Different Body Areas

Equipment

Procedure Preparation

Laser Hair Reduction: Steps and Principles⁷

The following recommendations are guidelines for hair reduction treatments using an intense pulsed light (IPL) device (Palomar StarLux 500 using the LuxRs handpiece). Manufacturer’s guidelines for the specific device used should be followed at the time of treatment.

Planning and Designing

A grid pattern may be drawn on the skin using a soft white pencil to help ensure complete coverage of the treatment area (Figure 26-5). This is particularly useful when treating large areas such as the leg and back.

FIGURE 26-5 Grid pattern for laser hair treatments.

(Copyright Rebecca Small, MD.)

Performing Laser Hair Reduction

1. Shave the treatment area if it is unshaven.

CAUTION: If hair is too long at the time of treatment, singed hair on the skin surface may result in epidermal injury.

2. Anesthetize the treatment area if necessary (see Anesthesia section above).

3. Provide appropriate laser-safe eye protection for the patient and all people in the treatment room prior to beginning treatment.

TIP: Always angle the laser tip away from the eyes during treatment.

4. Cover tattoos and permanent makeup with wet gauze and perform treatments at least 2 inches away from them.

CAUTION: Full-thickness burns may result from treating over tattoos.

5. Always operate the device in accordance with your clinic’s safety policies and procedures and the manufacturer’s guidelines.

6. Select the pulse width based on the patient’s Fitzpatrick skin type, using the manufacturer’s guidelines. Darker Fitzpatrick skin types (IV and V) require longer pulse widths due to their greater risk of epidermal injury. For example, the manufacturer may recommend 40- to 100-ms pulse widths initially for a Fitzpatrick skin type IV versus 20- to 30-ms pulse widths for a Fitzpatrick skin type II.

7. Refine the pulse width selection and the fluence using the manufacturer’s guidelines by assessing the hair characteristics in the treatment area including color, coarseness, and density. Coarse, dark hairs and areas with high hair density require longer pulse widths and lower fluences. For example, an initial treatment for a patient with Fitzpatrick skin type IV having black, coarse hair with high density may require a pulse width of 100 ms and fluence of 24 to 26 J/cm². The same patient with black, fine hairs with a sparse distribution may require a 40-ms pulse width and fluence of 30 to 32 J/cm².

8. Apply a clear colorless gel to the skin. Place the tip firmly on the skin, making certain that the entire tip is in contact with the skin and is surrounded by gel.

9. Perform a single pulse in the treatment area and assess for patient tolerance and clinical endpoints (see below). In general, there should be subtle endpoints with initial treatments and pain should be less than or equal to 6 on a scale of 1 to 10.

TIP: Ice may be used immediately prior to treatment to reduce discomfort. Application of ice to the treatment area after treatment also reduces the incidence of paradoxical hair growth.¹⁴

10. Desirable clinical endpoints for LHR treatments include:

• Singed hair smell

• Erythema (Figures 26-6, 26-7 and 26-8)

• Perifollicular edema (PFE) (see Figure 26-7)

• Singed hair (see Figures 26-6 and 26-8)

• Hair extrusion (see Figure 26-8).

11. Figure 26-7 shows the desired clinical endpoints of erythema, which develops rapidly, and perifollicular edema (PFE), which typically develops a few minutes after the pulse and indicates that the hair bulb has been effectively treated. PFE is more commonly seen with longer pulse widths.

12. Figure 26-8 shows the desired clinical endpoints of erythema, perifollicular edema, singed and extruded hair.

TIP: Clean the IPL tip between pulses with moist gauze to reduce the buildup of singed hair.

13. Continually assess laser/tissue interactions and clinical endpoints throughout the treatment and adjust settings accordingly.

14. For subsequent treatments, fluence is increased and pulse width decreased according to the manufacturer’s guidelines to target finer, lighter hairs. In general, only one parameter is changed to intensify treatments in any given visit. Typically, the fluence is increased initially for a few treatments to achieve desired clinical endpoints, and pulse width is decreased in later treatments.

TIP: Finer, lighter hairs are the most challenging to treat. It is important to inform patients that once hair becomes very fine and light, the efficacy limits of the laser may be reached. Subsequent, more aggressive treatments may not be of therapeutic benefit and may be associated with greater risks from high fluences.

15. The entire treatment area is covered at each laser hair treatment session.

16. Ice may be applied immediately after treatment to soothe the treatment area and reduce PFE.

17. A topical steroid may be applied to erythematous areas, such as 1% to 2.5% hydrocortisone cream.

18. A full-spectrum sunscreen (SPF 30 with zinc or titanium) is applied to sun exposed areas.

FIGURE 26-6 Laser hair treatment clinical endpoints of erythema and singed hair.

(Copyright Rebecca Small, MD.)

FIGURE 26-7 Laser hair treatment clinical endpoints of perifollicular edema and erythema.

(Copyright Rebecca Small, MD.)

FIGURE 26-8 Laser hair treatment clinical endpoints of erythema, perifollicular edema, and hair singeing and extrusion.

(Copyright Rebecca Small, MD.)

Results

After the first treatment, patients may experience a prolonged delay in hair regrowth from 1 to 3 months. This is temporary hair reduction, and although patients are usually very pleased with the lack of growth, they should be forewarned that regrowth will occur. Hair regrowth may appear in some parts of the treatment area and not others. This patchy regrowth is normal and indicates that a group of hairs in the anagen phase was effectively treated.

The greatest efficacy with permanent hair reduction is achieved with use of high fluences, a greater number of treatments, and adequately long intervals between treatments that approximate the telogen phase for the treatment area.⁶

Figure 26-9 shows hair reduction results for the anterior neck and chin (A) before and (B) after six treatments using an IPL (Starlux, Palomar).

FIGURE 26-9 Anterior neck and chin hair (A) before and (B) after completion of six hair reduction treatments with intense pulsed light.

(Copyright Rebecca Small, MD.)

Figure 26-10 shows hair reduction results for fine dark upper lip hair in a darker Fitzpatrick skin type (A) before and (B) after a series of treatments using a Q-switched 1064 nm laser. This is one of the only laser devices that can reduce fine hairs (RevLite, HOYA ConBio).

FIGURE 26-10 Upper lip hair (A) before and (B) after completion of a series of hair reduction treatments with a Q-switched 1064 nm laser.

(Courtesy of HOYA ConBio, Fremont, CA; J. Garden, MD, using laser.)

Figure 26-11 shows hair reduction results for the jawline and sideburns (A) before and (B) after completion of a series of treatments using a 755 nm laser (GentleLase, Candela).

FIGURE 26-11 Jawline and sideburn hair (A) before and (B) after completion of a series of hair reduction treatments with a 755 nm laser.

(Courtesy of Candela, Wayland, MA; M. Ercan, MD, using laser.)

Figure 26-12 shows hair reduction results for the axilla (A) before and (B) after completion of a series of treatments using a 755 nm laser (GentleLase, Candela).

FIGURE 26-12 Axilla hair (A) before and (B) after completion of a series of hair reduction treatments with a 755 nm laser.

(Courtesy of Candela, Wayland, MA; M. Ercan, MD, using laser.)

Figure 26-13 shows hair reduction results for pseudofolliculitis barbae in a patient with Fitzpatrick skin type VI (A) before and (B) after a series of treatments using a 1064 nm long-pulse laser (ClearScan YAG, Sciton).

FIGURE 26-13 Pseudofolliculitis barbae (A) before and (B) after completion of 12 hair reduction treatments with a 1064 nm long-pulse laser.

(Courtesy of Sciton, Palo Alto, CA; L. Haney, RN, using laser.)

Aftercare

Erythema and perifollicular edema usually resolve within a few hours to 1 week after treatment and can be managed with application of ice for 15 minutes every 1 to 2 hours and 1 to % hydrocortisone cream two to three times per day for 3 to 4 days or until resolved. Singed hairs may be evident immediately after treatment, and treated hairs may extrude 1 to 2 weeks after treatment. A washcloth may be used to wipe these hairs off in the direction of the hair follicles. Postinflammatory hyperpigmentation can occur with prolonged erythema, and patients are instructed to contact their provider if erythema persists for more than 5 days. Daily use of a full-spectrum sunscreen (SPF 30 with zinc or titanium) and sun avoidance for 4 weeks after treatment helps minimize the risk of pigmentary changes. If blistering and/or crusting occur, manage with moist wound care using bacitracin and a bandage until healed.

Follow-Up

Typical hair reduction treatment intervals include:

After completion of a treatment series, patients may require a touch-up treatment for dormant hairs that have entered the active growth cycle approximately 6 months to 1 year after completion of their series.

Complications

Rare and Idiosyncratic Complications

• Scarring

• Paradoxical hair growth

• Erythema ab igne, a rare reticular erythematous rash related to heat exposure with laser treatments

• Livedo reticularis, a rare autoimmune vascular disease associated with mottled skin and discoloration of the legs or arms exacerbated by heat exposure with laser treatments

• Urticaria, bruising, pruritus.

 

Pain is unavoidable with LHR because all hairs are innervated. Epidermal cooling methods and topical anesthetics can reduce discomfort, but most patients will complain of discomfort during treatment which significantly improves once the laser pulse ceases. Certain areas such as the upper lip, axillae, and genitalia are more sensitive than other areas.

Pigmentary complications are most commonly seen in darker Fitzpatrick skin types (IV and V) and in patients with a recent tan. These complications typically occur with short pulse widths and/or high fluences and poor epidermal cooling. Hyperpigmentation and hypopigmentation are usually transient, lasting on the order of months, and rarely may be permanent. The use of a lightening agent such as hydroquinone for 1 month prior to treatment and after treatment may reduce hyperpigmentation, particularly in darker skinned patients (see Chapter 24, Skin Care Products, for additional information).

A burn can result from aggressive treatment parameters of short pulse widths and high fluences with inadequate epidermal cooling. Figure 26-14 shows an erythematous area with crusting on the back 1 week after a laser hair reduction treatment. Routine moist wound care is performed with application of an antibiotic ointment and bandage until healed. Scarring is highly unlikely, but may occur with overaggressive treatments and with treatments complicated by infection.

FIGURE 26-14 Area of overtreatment with erythema and crust on the back after laser hair reduction treatment in a patient with Fitzpatrick skin type IV.

(Copyright Rebecca Small, MD.)

Herpes simplex and varicella zoster may be reactivated in the treatment area, and pretreatment prophylactic antiviral medication can reduce this risk (see the Procedure Preparation section above). Impetigo may occur, particularly with treatments around the mouth. Folliculitis may also occur, particularly after vigorous exercise, swimming or hot tub use immediately after treatments (Figure 26-15).

FIGURE 26-15 Neck folliculitis after laser hair reduction treatment.

(Copyright Rebecca Small, MD.)

Failure to reduce unwanted hair can be the result of undiagnosed hyperandrogenic conditions such as polycystic ovarian syndrome, suboptimal laser parameters, or intervals between treatment sessions that are too short. For example, if lower extremity LHR treatments are performed at monthly intervals, a large number of hairs will not have cycled out of telogen into anagen and treatments will be less effective.

Hair grows at an angle to the skin and it is possible to unintentionally reduce hair growth adjacent to the treated area. Providers are cautioned against treating near the eyebrows for this reason. Paradoxical hair growth has been described, whereby LHR treatments stimulate hair growth. In this case, LHR may cause conversion of vellus hairs to coarse terminal hairs in the treatment area, or stimulate fine hair growth adjacent to the treatment area. Most cases are reported in skin types IV through VI, particularly with treatment of fine hairs in the lateral face.¹⁴ One study found that immediate application of ice around the treatment area and two passes of the laser in the treatment area reduced the risk of paradoxical hair growth.¹⁵

Tattoos and permanent makeup have concentrated ink pigments and treatment over these may result in epidermal injury. Ocular injury can be avoided by wearing appropriate laser-safe eyewear at all times during treatment, directing the laser tip away from the eye, and treating outside of the eye orbit.

Erythema ab igne and livedo reticularis are extremely rare, as is bruising, pruritus, and urticaria.

Special Populations

Learning the Techniques

Providers may initially perform laser hair reduction treatments on patients with light Fitzpatrick skin types (I through III) who have dark, coarse hair to minimize the risk of side effects and for ease of visualizing clinical endpoints. Axillae are a preferred area to start with as they are usually minimally sun exposed and have coarse hair.

Current Developments

Some of the newer laser hair reduction devices have larger treatment heads to shorten treatment times. Analgesic devices, such as pneumatic skin-flattening tips are available for LHR devices to reduce the discomfort associated with treatment¹⁶ (see Chapter 20, Anesthesia for Cosmetic Procedures). Recently, laser hair reduction devices have become available for use at home. One such device, Tria (by TriaBeauty), is a diode laser (810 nm) that has a long pulse width of 400 ms and low fluences of 7 to 20 J/cm². Another device, Silk’n (by Home Skinovations), is an IPL with a pulsewidth of less than 1 ms and low fluences of 3-5 J/cm². Data is limited on these devices and they will likely provide temporary hair reduction given their limited treatment parameters.

Financial Considerations

LHR is not reimbursable by insurance. The charges for treatments are usually based on the size of the treatment area and are largely determined by local prices. Patients may pay for individual treatments. However, because LHR is only effective with a series of treatments, packages of treatments (usually six) may be offered so that patients achieve the best possible results and have the greatest satisfaction. Box 26-1 lists applicable codes for LHR procedures.

Conclusion

Lasers and intense pulsed light devices can effectively reduce unwanted hair. A series of treatments is required, typically six for lighter Fitzpatrick skin types (I through III) and eight or more for darker skin types (IV and V). Laser hair reduction is generally well tolerated and has a low risk of side effects and complications with proper use of these devices and appropriate selection of treatment parameters.

Resources

See the Aesthetics Buyers Guide (www.miinews.com/productcharts.php) for specific laser technologies made by laser companies.