Key points
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Laser hair removal is now accepted as the safest and most effective technique for the removal of unwanted terminal pigmented hairs.
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A variety of laser/light source wavelengths have been successfully used for the removal of unwanted hair growth.
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Guidelines for effective laser hair removal continue to evolve.
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Complications from laser hair removal are rare, but clearly do occur.
Introduction
Requests for removal of unwanted body hair are common in dermatologic and surgical practices. Technology continues to improve in achieving a more permanent reduction through the use of lasers. Despite the increased use of lasers, to date, few guidelines exist in terms of how to approach laser hair removal. Specifically, one must understand the mechanism of hair growth and how lasers work to target the hair follicle. There is significant variation among practitioners in pre and post laser recommendations to patients, as well as intervals between treatment sessions.
Laser hair removal has become a widely accepted treatment modality for long-term hair reduction. This approach has come to rival electrolysis in the successful treatment of small hair bearing areas. It surpasses any modality in the treatment of larger hair-bearing areas as well as in those who have darker skin. This chapter describes laser hair removal, mechanisms of action, available technology, complications and a look at guidelines for successful laser and light-based hair removal.
Indications and patient selection
Those seeking removal of unwanted hair fall into three major categories:
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Some patients present with hypertrichosis. Hypertrichosis is defined as an increase in hair growth that is not androgen dependent. It may result from intake of certain medications such as phenytoin, cyclosporine, various steroids or penicillamine. Hypertrichosis has also been seen in a variety of diseases such as porphyria cutanea tarda, thyroid disorders, metastatic carcinoma, and malnutrition and/or anorexia nervosa.
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Some patients present with hirsuitism. Hirsuitism is characterized by the growth of terminal hair in women on androgen-dependent areas of the body. These anatomic areas include the upper lip, chin, or chest. Because hirsuitism is often the result of androgen excess, it may be accompanied by acne, androgenetic alopecia, and irregular menstrual cycles. The most common hormonal cause of hirsutism is polycystic ovary disease, estimated to occur in 1–4% of the female population of reproductive age. Rapid onset of hirsuitism or other signs of androgen excess should prompt a hormonal evaluation, to rule out the presence of an androgen secreting tumor.
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Most individuals seek consultation for unwanted hair, primarily because of cosmetic concerns. Facial or body hair in excess of the cultural norm can be very distressing to some patients. The most common areas treated include the axillae, bikini line, legs, and face in women, and the chest, back, shoulder, neck, and ears in men.
Understanding the biology of hair
Hair biology
It has always been assumed that the hair shaft was produced by rapidly dividing matrix stem cells located in the deepest portion of the hair follicle, 2–7 mm below the skin surface. However, recent evidence suggests that follicular stem cells are located in the outer root sheet, in an area called the bulge, near the attachment of the arrector pili muscle, approximately 1.5 mm below the epidermis. Thus both bulge and bulb are important targets for permanent hair follicle destruction.
Animal studies have shown that the hair growth cycle affects the hair follicle destruction by ruby laser pulses: actively growing and pigmented anagen stage hair follicles were sensitive to hair removal by normal mode ruby laser exposure, whereas catagen and telogen stage hair follicles were resistant to laser irradiation. However, in humans, the efficacy of laser hair removal does not appear to always be influenced by the hair growth cycle. Unlike the animal model, there is enough melanin present in each growth cycle of the human hair follicle to obtain selective damage to the hair.
A recent study showed no acute changes in the immunohistochemical staining properties of hair follicles treated with an 800 nm diode laser or a 1064 nm Nd : YAG laser. These findings challenge the widely accepted belief that the mechanisms of laser hair removal are mediated by frank destruction of follicular stem cells. Instead, functional alterations of these cells may lead to the desired clinical outcomes. Future studies may elucidate the exact mechanism of laser hair removal.
Light destruction of hair
There are three ways light can potentially destroy hair follicles: thermal (due to local heating), mechanical (due to shockwaves or violent cavitation), and photochemical (due to generation of toxic mediators like singlet oxygen or free radicals). All of these methods have been used in light based hair removal.
Techniques
Photothermal destruction
Photothermal destruction is based on the principle of selective photothermolysis. This principle predicts that selective thermal damage of a target structure (such as a pigmented hair) will result when sufficient fluence at a wavelength, preferentially absorbed by the target, is delivered during a time equal to or less than the thermal relaxation time of the target.
The millisecond 694 nm ruby, millisecond 755 nm alexandrite, 800 nm pulsed diode lasers, long pulsed millisecond 1064 nm Nd : YAG lasers, and filtered flashlamp technology, alone or in combination with electrical energy from radiofrequency, all employ this mechanism.
In the visible to near infrared region, melanin is the natural chromophore for targeting hair follicles. Lasers or light sources that operate in the red or near-infrared wavelength region deliver light-based energy in this spectrum, where selective absorption by melanin is combined with deep penetration into the dermis. Deep, selective heating of the hair shaft, hair follicle epithelium, and the heavily pigmented matrix is therefore possible in the 600–1100 nm region. However, melanin in the epidermis presents a competing site for absorption. Selective cooling of the epidermis has been shown to minimize epidermal injury. Cooling can be achieved by various means, including a cooled gel layer, a contact cooled chamber or window, air cooling, and a pulsed cryogen spray.
Laser pulse width also appears to play an important role in laser hair removal, as explained by the thermal transfer theory. Thermal conduction during the laser pulse heats a region around each microscopic site of optical energy absorption. To obtain spatial confinement of thermal damage, the pulse duration should be shorter or equal to the thermal relaxation time of the hair follicle. Thermal relaxation of human terminal hair follicles has never been measured, but is estimated to be about 10–50 ms, depending on the size of the treated hair. This explains why current laser hair removal devices emit pulse durations in terms of milliseconds.
Photomechanical destruction
Photomechanical destruction as the result of small local ‘explosions’ are induced by Q-switched laser pulses. It should be noted that unlike photothermal millisecond pulses, nanosecond Q-switched laser pulses effectively damage individual pigmented cells within hair follicles by confinement of heat at the spatial level of melanosomes. Because of this, only temporary hair loss has been seen after over a decade of treating tattoos in hair bearing areas with Q-switched lasers.
Photochemical destruction
Photodynamic therapy is the use of light and a photosensitizer to produce a targeted photochemical reaction and therapeutic effect. ALA is a precursor in the porphyrin synthesis and is rapidly and selectively converted to protoporphyrin IX (PPIX) by cells derived from the epidermis and follicular epithelium. Upon absorption of a photon, PPIX efficiently crosses into an excited triplet state, which in turn generates singlet oxygen by collision with ground state oxygen. Singlet oxygen is a potent oxidizer that damages cell membranes and protein. This is a so called photodynamic reaction. A host of other topical substances can act as photodynamic agents and are being investigated for their roles in photodynamic therapy. It is likely that ALA or one of these other drugs will prove useful for hair removal. This approach will potentially provide an effective means of treating non-pigmented hair.
Laser and light source hair removal wavelengths
694 nm ruby laser
Because of high melanin absorption at 694 nm, the ruby lasers have historically been very popular for light skinned individuals with dark hairs. Because of this limitation, their large size, poor service records and relatively slow repetition rate, ruby lasers have become less popular and are rarely used today. In fact millisecond ruby lasers sold today are usually packaged with the more popular tattoo and pigmented lesion nanosecond Q-switched ruby lasers ( Figure 7.1 ).
755 nm alexandrite lasers
Long-pulsed alexandrite lasers (755 nm) are effective, highly popular devices for hair removal. At this longer wavelength, the ratio of energy deposited in the dermis to the epidermis is greater because of greater depth of penetration. The risk for epidermal damage in darker skin types is therefore reduced when compared to ruby lasers but this wavelength is typically used in light skinned patients with dark hair ( Figure 7.2 ).
800 nm diode lasers
High-powered diode lasers are also very popular. Long-term results suggest that the pulsed, 800 nm diode laser is very effective for removal of dark, terminal hair. Similar to what is seen with the 755 nm alexandrite laser, permanent hair reduction can be obtained in a significant percentage of patients. In addition, because of the longer wavelength, active cooling, and the longer available pulse widths with this laser, darker skin types can be treated more safely than with ruby and alexandrite lasers ( Figure 7.3 ).
Q-switched 1064 nm Nd : YAG laser
High-powered, Q-switched 1064 nm Nd : YAG lasers are also used for hair removal. The longer wavelength (1064 nm) makes this system useful for darker skin types. Although capable for inducing a growth delay, it appears that the emitted nanosecond pulse is generally ineffective for long term hair removal.
Long-pulsed 1064 nm Nd : YAG lasers
Several long-pulsed millisecond 1064 nm Nd : YAG lasers are now available for hair removal laser treatment on all skin types.
The long pulsed Nd : YAG lasers emit deeply penetrating 1064 nm wavelengths. The reduced melanin absorption at this wavelength necessitates the need for high fluences in order to adequately damage hair. However, the poor melanin absorption at this wavelength coupled with epidermal cooling device makes the long pulsed Nd : YAG laser a safer laser treatment for darker skin types up to phenotype VI. All skin types as well as tanned patients may be treated with lasers at this wavelength ( Figure 7.4 ).
