Laser Hair Removal

Anatomy and Physiology

Selective Photothermolysis

Lasers for skin treatment work on the theory of "selective photothermolysis." This term implies a site-specific, thermally mediated injury of microscopic tissue targets by the selective absorption of pulses of radiation by the targets and the chromophores. The natural or artificial chromophores absorb monochromatic or broadband electromagnetic radiation of specific wavelengths. The chromophore employed in laser hair reduction is melanin. Melanin absorbs light in the range of 300 to 1200 nm, and lasers in this range of wavelengths can be effectively used for hair reduction.[3][4]

An Extended Theory of Selective Photothermolysis

Target absorption may not always be uniform. In these cases, the weakly absorbing parts may have to be destroyed by heat diffusion from the highly absorbing parts. This is the "extended theory of selective photothermolysis." This principle is applied to laser photoablation. Melanin content is much higher in melanin-bearing structures like the hair shaft and matrix cells than in the hair follicle. Thus melanin captures energy from the laser and distributes it to the surrounding follicular structures. This results in the destruction of the hair matrix and hair bulge stem cells.[5]

Indications

1. Hirsutism and hypertrichosis
2. Aesthetic purposes
3. Medical indications like pseudofolliculitis barbae, pilonidal sinus, and acne keloidalis nuchae.[6]

Equipment

Lasers for hair reduction include the following:

1. Ruby Laser (694 nm) - Red light is delivered through synthetic ruby crystals, more effective for lighter skin types with dark hair (skin types I-III*)[7]
2. Alexandrite Laser (755 nm) - Greater penetrance, good for lighter hair (skin types I-III)[8]
3. Diode Laser (810 nm) - Penetrates deeper, delivers better fluence, less epidermal damage, safer in darker skin (skin types I-V)[9]
4. Neodymium-doped Yttrium-Aluminium-Garnet (Nd: YAG) Laser (1064 nm) - Better penetration, less epidermal damage, relatively less melanin absorption (skin types I-VI)[10]
5. Intense Pulse Light (IPL) or Broadband Light (BBL) (500-1200 nm) - High-intensity pulses of polychromatic, non-coherent light are delivered by a flash-lamp; various filters allow the narrowing of the emitted wavelength band, can be used on darker skin, larger areas can be covered due to its larger spot size, less expensive than a true laser but not as effective[11][12][13]

* Fitzpatrick Skin Types[10]

• I- Pale white skin, blue/green eyes, blond/red hair; always burns, does not tan
• II- Fair skin, blue eyes; burns easily, tans poorly
• III- Darker white skin; tans after the initial burn
• IV- Light brown skin; burns minimally, tans easily
• V- Brown skin; rarely burns, tans darkly easily
• VI- Dark brown or black skin; never burns, always tans darkly

Preparation

1. Detailed clinical history to rule out infections, drug intake, etc.
2. Hormonal evaluation to assess causes of hirsutism.
3. Counsel the patient to manage expectations. It must be stressed that the procedure provides permanent hair reduction rather than removal.
4. Evaluate skin and hair types to choose the right laser and parameters.
5. Avoid hair epilation by plucking or waxing for 6 weeks before the procedure.
6. Sunscreens may be prescribed 4 to 6 weeks before the procedure, especially on exposed areas.
7. Pre-procedure photographs, with due consent, to maintain a record for evaluation of treatment response.
8. Shave the area long enough before the procedure to allow a slight stubble to develop; this will provide enough of a target for the laser without absorbing too much energy in the hair shaft itself.
9. Obtain an informed consent.
10. If need be, a topical anesthetic cream may be applied one-half to one hour before the procedure.[14][15]

Technique or Treatment

1. Clean the area to remove oils from the skin
2. Position the patient comfortably.
3. Use eye protection for both the operator and the patient.
4. Avoid reflecting surfaces or metallic objects near the laser.
5. Individualize the parameters to each patient's skin and hair type and the type of laser being used. 
6. Place the handpiece perpendicular to the skin. Ensure that it is pressed down gently but firmly to bring the follicles close to the surface and temporarily decrease the blood supply to the treatment area.
7. Perifollicular edema and erythema is an expected side effect, and this must be explained to the patient prior to the procedure.[14][15]

Post-Procedure Care

1. Although most machines have inbuilt cooling systems, ice packs or cooling agents may be used post-procedure to minimize pain and swelling.
2. In case of inadvertent epidermal injury, topical antibiotics may be used.
3. Strict sun protection and the use of sunscreens is a must.
4. Topical steroid creams may be prescribed to minimize erythema and swelling.[14][11]

The hair matrix is only sensitive to laser treatment during the anagen phase of the hair growth cycle; therefore multiple treatments will be necessary in order to address all hair follicles when they are most sensitive to treatment. In the initial phase of hair removal therapy, 4 to 6 sessions spaced 4 to 6 weeks apart are the minimum required to achieve adequate results. Subsequently, patients may need maintenance treatments once every 6 to 12 months as small vellus hair may grow back.[16]

Various factors may affect the outcome, such as:

1. Hair location (axillary and pubic hair respond better than hair on the extremities and chest)
2. Skin and hair color (light skin of Fitzpatrick skin types I-IV with dark hair achieve the best results due to the lack of melanin in the skin and the abundance of melanin to absorb laser energy in the hair follicles)
3. Hair growth stage (anagen hair being most sensitive)
4. Laser type
5. Hormonal status
6. Treatment plan[2]

Complications

Adjacent epidermal structures other than melanin within the hair bulb can compete for absorption, and may cause laser energy to be absorbed by pigment in the epidermis. This hampers the effectiveness of the treatment and causes adverse effects due to adjacent epithelial damage. [17]

Common adverse effects of laser or IPL-based hair removal include post-treatment erythema, pain, and burning.[18]

More severe adverse effects include blistering, crusting, dyspigmentation, purpura, and sometimes scarring.[19][20] Ocular complications due to accidental injury may be seen. Paradoxical hypertrichosis may rarely occur, more commonly in skin type III and with the use of IPL systems.[21][22][23]

Clinical Significance

Selecting the correct lasers with the appropriate parameters, individualized to each patient, is very important, particularly in patients with intrinsically dark skin. Most complications are preventable when adequate precautions are taken with adjustment of the fluence, spot size, wavelength, and the use of appropriate cooling. Thus, it is all the more important that trained personnel with a thorough knowledge of the mechanisms, techniques, and complications carry out these procedures.

Enhancing Healthcare Team Outcomes

Laser hair removal is performed by many healthcare workers including nurses, dermatologists, plastic surgeons, primary care providers and other cosmetic surgeons. Unfortunately, because of lack of oversight, complications are common during this procedure. To make matters worse, patients are often given unrealistic expectations. The key is to use the correct laser, especially in dark skinned individuals. Common adverse effects of laser or IPL-based hair removal include post-treatment erythema, pain, and burning.[18] More severe adverse effects include blistering, crusting, dyspigmentation, purpura, and sometimes, scarring.[19][20] Ocular complications due to accidental injury may be seen. Paradoxical hypertrichosis may rarely occur, more commonly in skin type III and with the use of IPL systems.[21][22][23]

Overall, lasers can remove hair but rarely does the procedure provide a permanent cure for hair growth. Touch up maintenance treatments are required for most patients in the long term.