The hair follicles are specialized structures in the skin that produce hairs. I think of them like tulip bulbs. They are planted deep in the skin. In fact, they stick out of the underside of the skin. They are well-protected in this location. Any treatment to remove the hairs without damaging the skin must be selective. The puzzle has always been, how does one destroy the hair follicle without damaging the surrounding skin?

Hair removal has always been made difficult by the location of the hair follicles, which are deeply situated in the skin. Lasers that nonselectively remove the top layers of the skin are therefore ineffective. Sometimes patients ask if the resurfacing lasers such as the erbium:YAG laser and the CO₂ laser will get rid of their facial hair. They will vaporize surface hair, but because these wavelengths do not penetrate deeply into the dermis, the hair follicle is unaffected. A new hair grows out to replace the vaporized one.

However, lasers that produce wavelengths that penetrate more deeply into the skin are ideally suited for this purpose. All that remained was a suitable target which could absorb the laser energy and deliver it to the hair follicle.

For years, lasers have been used to treat a variety of skin conditions, such as port wine stains, benign pigment conditions and tattoos. In 1983, the concept of Aselective photothermolysis@ was introduced. This described the use of medical lasers of the appropriate wavelength and energy settings to act on targets in the skin, without causing damage to the surrounding tissue.

There was no such thing as Alaser hair removal@ before the 1990's. Like so many important discoveries (microwaves for example), the use of a laser for hair removal was discovered by accident, while lasers were being used for tattoo removal. Doctors noticed that when they treated tattoos with a ruby laser, fewer hairs grew back in the treated area, introducing a new application of the laser to the old problem of hair removal. The laser target was the pigment in the skin.

Fortunately, you don’t need to have a tattoo for the treatment to work. Pigment cells containing melanin are concentrated around hair follicles. Melanin is a naturally-occurring pigment in the skin that may be targeted by a laser using a wavelength that is well absorbed by melanin. By absorbing and then releasing the laser energy next to the hair follicle, the follicle may be disabled. The energy is concentrated in a very short pulse (milliseconds), so that heat does not build up sufficiently to cause damage to the surrounding skin cells. In this way, hair follicles may be safely deactivated, with minimal risk of scarring.

In 1991 the use of the ruby laser for hair removal was patented. Several clinical studies were performed, and in 1997, the FDA approved three types of ruby lasers for hair removal, including the EpiTouch and the EpiLaser. The FDA-approved alexandrite and diode lasers, with similar specificity for melanin, were introduced shortly afterward. Our facility has considerable experience with the long-pulsed alexandrite Apogee® laser (Cynosure Inc., Westford, Mass.).

The ruby (694 nm), alexandrite (755 nm), and diode (810 nm) lasers all have wavelengths that are appropriate for hair removal. Shorter wavelengths are more absorbed by melanin, but do not penetrate as deeply into the skin. The alexandrite laser provides a favorable balance of penetration and melanin absorption.

The Nd:YAG laser has a wavelength of 1064 nm. Consequently, it penetrates more deeply into the skin but at the price of much reduced melanin absorption. To compensate for this, a topical black carbon-mineral oil preparation was rubbed into the skin to act as a target for the laser energy. In fact, this was the first laser system marketed for hair removal (Softlight, manufactured by Thermolase). Patients needed to be waxed first to remove the hairs from the follicles and let the lotion penetrate the hair follicles. The need for waxing and a rubbed-in ointment were obvious disadvantages and it is no longer used. However, the Nd:YAG laser is sometimes used today to treat patients with dark skin types (Fitzpatrick V and VI) who cannot be treated with the newer systems, but the poor melanin absorption compromises its effectiveness.

Our center first used the ruby laser before switching to the long-pulsed alexandrite laser. The alexandrite offered advantages – a larger spot size and faster repetition rate, reducing treatment times and making them less expensive. Also, the longer “pulse duration” offered at least a theoretical advantage in delivering more energy per pulse. Although the evidence is anecdotal, our patients seemed to require fewer treatments with the long-pulsed laser. A cooling unit that blows refrigerated air over the skin provides sufficient cooling, reducing discomfort. Topical anesthetic cream such as EMLA is not required.

There are alternative Intense Pulsed Light (IPLTM) systems (such as EpilightTM) that use a flashlamp and then a filter to narrow the range of wavelengths. These light-based systems are sometimes confused with lasers. The advantage of laser treatment is specificity. All of the energy is delivered on the desired wavelength so that there is less wasted energy.

Most areas of the face and body may be treated. Women often wish to have the upper lip, chin, lower face and neck treated. These are common areas of unwanted hair, usually an inherited tendency. They are typically treated in 20 minutes or less. The bikini area and underarms are also commonly treated. The arms and legs are larger areas that may be treated and will take longer.

Men may experience overgrowth of hair in the beard area. The lower face and neck may be treated to reduce growth in these areas. This may also reduce ingrown hairs and folliculitis. The back of the neck, shoulders, and back are often treated. These areas are large and require a longer treatment session, usually over an hour.

While laser treatment is a huge step forward, making possible what was previously impossible, it is not perfect. Hair follicles are not all vulnerable to the laser treatment at one time, so it’s not possible to eliminate them all in one laser treatment. Hair follicles cycle, from a dormant resting stage of invulnerability (“telogen”) to the growth phase (“anagen”), a brief breakdown phase (“catagen”) and then back to their “hibernating” telogen phase again. The cycle length is different, depending on the anatomic location. For most areas of the body, it’s between 4 and 10 months long and about half this time is spent in the anagen phase. The scalp has a much longer anagen phase, accounting for the longer hair length of scalp hairs.

Of course, the hairs are not all in the same phase of their cycle. They only seem to be vulnerable to laser treatment in their growth phase. Perhaps this is because only during this phase there is a hair shaft present in the bottom of the follicle to absorb laser energy (the reason to avoid plucking before laser hair removal). Additionally, hair follicles that are in anagen may not be permanently deactivated with a single laser treatment. A significant percentage will survive, although the hair may be less coarse and lighter. Consequently, laser hair removal cannot effectively remove all the hair in one treatment. This is why treatments are spaced out at least a month apart, so that hairs emerging from their “hibernation” can be treated. Over the course of treatments, few hair follicles will escape exposure to the laser energy.