Summer is approaching, and as your patients start to show more skin, they may also reveal some old tattoo or unwanted hair that was conveniently covered up during winter. In fact, they may decide that this is the year where they want to be free of the stubble or colourful adornments, and they may ask you about their options for hair and tattoo removal. Here’s what you need to know about what laser treatment can do in this respect.
A versatile approach
The word LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. By definition, lasers emit a single wavelength or a very narrow band. The emission spectrum depends on the type of active medium used (Table 1).
Light from a laser can be continuous or pulsed. Continuous lasers have a limited peak power while pulse waves can deliver high-energy radiation in short bursts, and are critical for targeted therapy. When a laser beam hits the skin, a small amount of light (< 10%) is reflected at the surface, and the rest is scattered, transmitted or absorbed in the skin. Only absorbed radiation has a clinical effect that can be harnessed for hair or tattoo removal.
Absorbing skin molecules — called chromophores — receive energy from the absorbed photons. Examples of important chromophores in this context include melanin, water and hemoglobin. Melanin absorbs broadly across the spectrum, while hemoglobin absorbs light < 700 nm, and water absorbs predominantly in the infrared range of the spectrum (> 700 nm).
For wavelengths between 280 and 1,300 nm, there’s a direct relationship between the depth of penetration and wavelength. In addition, the size of the spot produced by the laser affects penetration — the larger the spot, the greater the chance that more photons will go deeper into the skin.
What happens inside the skin
When laser energy is absorbed, it’s converted to heat, which dissipates from the chromophores into surrounding tissues. To minimize heat injury, the target should be treated for a shorter amount of time than it takes to lose half of the heat. So if the properties of the material are known, laser therapy can be applied with minimal damage to surrounding tissue by selecting the appropriate wavelength, pulse duration and energy delivered. It’s important to keep in mind that chromophores in neighbouring locations may be affected unintentionally. For instance, melanin in the epidermis may absorb radiation — leading to epidermal injury — when melanin in the hair follicle is the intended target. For this reason, skin cooling either before or during laser therapy is essential.
Tattoos may be done for cosmetic appeal or as marking for medical procedures, or they may be due to trauma (e.g. gunpowder, lead). Many techniques have been tried for removal — including cryosurgery, surgical excision, dermabrasion and caustic chemicals — but all these methods are likely to cause scarring. Laser therapy, when done by a skilled professional, is arguably a more effective option with less likelihood for scarring. There’s no guarantee of complete removal, however, as nearly a third of patients will have persistent tattoo markings despite multiple laser sessions.
Each type of ink constitutes a distinct chromophore, i.e. different tattoo colours require a variety of lasers (Table 2). The absorbed light energy breaks apart the ink molecules and destroys pigment-containing cells. Broken-up ink particles are then carried away by lymphatics. Depending on the size, type of pigments used, density of pigment, and age of the tattoo (fresh tattoos are more difficult), patients will need up to 5-10 treatments for best results.
Although lasers produce local pain, anesthetics are rarely necessary. Right after treatment, there’s local whitening of the skin that resolves within an hour. A crust soon forms and falls off after 2 weeks. Purpura can develop if hemoglobin is unintentionally targeted; it may last up to 1 week.
Other side effects include pigmentary changes. Darker skin, because of its higher content of epidermal melanin, is at greater risk, so lower energy settings are used. There can also be paradoxical darkening of the tattoo, especially for brown, red and white ink. Less common side effects include microexplosions (gun powder) and allergic contact dermatitis reactions due to chromium contained in green ink, cadmium in yellow pigment and mercury, cadmium and azo dyes in red tones.
Perhaps the most popular cosmetic use of lasers is for hair removal. The laser destroys stem cells of the hair follicle so that a new hair follicle can’t regrow. Unfortunately, there are no chromophores in the stem cells. Instead, melanin in the hair shaft is targeted — with longer pulse durations, heat will diffuse to neighbouring stem cells, resulting in their destruction.
Hair loss can be temporary or permanent. Lower energy lasers may only induce catagen, i.e. the shedding phase of the hair cycle, and temporary hair loss. Higher energies produce permanent hair loss by either causing hair follicles to shrink — in which case they only grow fine, colourless hair — or by completely destroying the hair follicle, inducing fibrosis.
Because the hair follicle is located in the dermis, longer wavelengths are required for adequate penetration. Red to near-infrared lasers are best; Nd:YAG lasers are considered safest, followed by Diode and Alexandrite. The main downfall of relying on melanin in the hair follicle is that hair with minimal melanin (e.g. red and blond) is much more difficult to treat. There’s also a risk of damage to epidermal melanin, which may result in permanent pigmentary changes. Skin cooling can minimize this effect and is especially important in dark-skinned individuals.
Multiple treatments are required for good results. After a single session, only 20-30% of treated hairs will be permanently lost, assuming optimal technique. There may be up to 90% hair loss after 10 treatments. Sessions should be spaced in 2-3-month intervals to allow hair to regrow.
As with tattoo laser therapy, local anesthesia is rarely required. Pigmentary changes, affecting up to 5% of individuals, are more likely in those with dark skin. All patients should be instructed to avoid the sun after laser therapy and to use sunscreen. Blistering occurs with epidermal injury, and local inflammation can last up to 3 days following treatment. Shaving hair before a treatment helps reduce damage. If a person is known to have keloidal scarring or skin diseases such as psoriasis that occur at sites of trauma, extra care should be taken.
Charles Lynde, MD, FRCP(C) is an assistant professor of Dermatology at the University of Toronto.
John Kraft, MD, is in his second year of the Dermatology Residency Program at the University of Toronto.
Table 2 - Lasers used for different tattoo inks