According to the American Society for Aesthetic Plastic Surgery, laser hair removal popularity has increased by 53 percent in one year, ranking it as the second most popular nonsurgical cosmetic procedure performed.
The importance of understanding the laser and light systems available for hair removal cannot be overemphasized, as this field continues to grow in popularity.
The alexandrite laser emits energy at a wavelength of 755 nm — well within the absorption spectrum for melanin. As melanin is the target chromophore for hair removal, this makes the laser a great device for removing hair.
There is a caveat to this shorter wavelength, and that is why we see less tissue penetration at shorter wavelengths. This is one of the reasons why the ruby laser became obsolete for epilation. The hair follicle is located at a depth of 2 to 3 mm in the skin. In order to compensate for less penetration of the wavelength, we need to have a larger spot to deliver more effective energy at a greater depth. For successful delivery of energy to the follicle, the alexandrite laser used should have a spot size of at least 12 mm. One group showed an increase in hair reduction of 10.3 percent when using an 18 mm spot size versus a 12 mm spot size.
Several groups have looked at the effectiveness and the side effects of the alexandrite laser for hair removal. Most reports indicate that the alexandrite is equally as effective as the diode laser for hair removal for skin types I through IV. With lighter hair, the alexandrite outperforms the Nd:YAG systems, and as far as tolerability, it is generally found to be less painful than the Nd:YAG.
Managing melanin absorption
There are pros and cons to using a laser that has a wavelength with a high absorption by melanin.
Laser energy from the alexandrite may be effectively absorbed by the melanin in the hair shaft, but it may also be absorbed by the melanin in the epidermis. Absorption by melanin in the skin by the laser will result in hypopigmentation. In fact, the Q-switched version of the alexandrite is very effectively used for pigment removal in tattoos and lentigines.
Post-inflammatory hyperpigmentation can also be seen in the darker skin types when using the alexandrite laser. Most of these complications are reversible. Patient selection needs to be done carefully. In our practice we seldom initially use the alexandrite on skin types IV and darker. When it is used on these darker skin types, pigmentary side effects can be expected.
In general, most of these are temporary in nature. Treatment of non-sun-exposed areas, such as the axillae, will generally result in much fewer complications than treatment of sun-exposed areas such as the legs or face. Altered pigmentation in the area of treatment delays further laser treatment and definitely results in a dissatisfied, if not completely unhappy, patient.
Another way of reducing pigment complications with the alexandrite is to increase cooling to the epidermis. Most alexandrite systems have adjustable cooling mechanisms, allowing the user to increase the length of the cryogen spray when using on darker skin types, or lengthening the contact time of a cooling tip. Dover et al showed that the benefits of cooling are apparent with a cryogen spray duration of 20 to 60 ms. No added benefit was seen with a spray duration longer than 60 ms.
Another factor making the alexandrite laser less user-friendly for darker skin types is its relatively fixed pulse width. Most of the diode lasers available now have adjustable pulse widths, in the super long pulse range. The typical alexandrite has a pulse width of 2 to 40 ms, whereas some of the long-pulsed diodes have pulse widths up to 1,000 ms. This has the potential to make the diode a more "epidermally protective" laser hair removal system. One study showed that by lengthening the pulse duration on the 755 nm laser, there was a trend toward less post-treatment erythema and pigmentation without the sacrifice of efficacy.
Another way to protect the epidermis is to lower the fluence of the laser. However, we know that the higher the fluence used, the more effective the hair removal. So, if the patient's skin can only tolerate the laser at a very low fluence, it is best to switch to a longer-wavelength laser.