Tattoo Anatomy

During the tattooing process, tattoo ink is injected intradermally. The epidermis and upper papillary dermis are homogenized and ink particles (ranging in size from 2 to 400 nm) are deposited intracellularly and extracellularly. After 2 to 3 months, the skin layers are reestablished and ink is concentrated in the dermis within fibroblasts, beneath a layer of fibrotic scar tissue (Figure 30-2).

FIGURE 30-2 Tattoo placement and dermal incorporation of ink (A) immediately after tattooing, (B) 1 month, and (C) 2 to 3 months after.

Numerous chemicals and inks are used in the tattoo industry and the component ink compounds in a given tattoo are usually unknown by the patient at the time of presenting for tattoo removal. The Food and Drug Administration (FDA) does not regulate tattoo inks and, therefore, tattoo inks are not evaluated for safety. In general, amateur tattoos are often carbon based such as burnt wood or pen ink, and there is a lower density of pigment particles. Professional tattoos are typically composed of organic dyes mixed with metallic elements that give the color: red is often made from mercury; yellow from cadmium; green from chromium; blue from cobalt; white from titanium dioxide; and flesh color from iron oxide. Tattoo inks are usually combinations of colors, so a green, red, or light blue tattoo may also contain darker colors such as black ink.

Laser Principles

Tattoo ink serves as a cutaneous chromophore for lasers. Certain wavelengths of light are selectively absorbed by different ink colors.⁴ In this way, colored inks can be targeted and removed by laser light with minimal damage to surrounding tissues. The chromophore absorption spectrum of the tissue chromophores, melanin and oxyhemoglobin, as well as wavelengths used for tattoo removal, are shown in Figure 30-3. Wavelength selection for different tattoo colors is shown in Figure 30-4 and is as follows:

FIGURE 30-3 Chromophore absorption spectra and tattoo removal lasers.

FIGURE 30-4 Laser wavelengths used for different tattoo colors.

(Copyright Rebecca Small, MD.)

• Black and dark blue inks are best treated with a 1064 nm wavelength.

• Red ink (and variations of red such as orange and yellow) is best treated with a 532 nm wavelength.

• Green ink is best treated with 650, 694, or 755 nm wavelengths.

• Sky blue is best treated with a 585 nm wavelength.

• Purple is a combination color and can be treated with 585 and 532 nm wavelengths.

Laser parameters including wavelength, pulse duration, and fluence can be tailored to maximize tattoo ink destruction and minimize thermal damage to surrounding tissue. Short pulsed, Q-switched lasers further employ photoacoustic vibration to fragment tattoo ink into smaller particles. These smaller ink particles are eliminated through epidermal extrusion, lymphatic drainage, and macrophage phagocytosis. In addition, laser-treated ink particles have altered optical properties that render the ink remaining in the skin less visible to the eye.⁵

Laser Parameters and Tattoo Treatments

• Pulse width, or pulse duration (measured in nanoseconds) is the length of time that laser light is in contact with the skin. Q-switched lasers have fixed nanosecond pulse widths and this parameter cannot be adjusted for treatments.

• The thermal relaxation time (measured in seconds) is defined as the time required for the absorbed energy within the target chromophore to cool to one-half its original value immediately after irradiation. To specifically target the chromophore ink and reduce unwanted thermal damage to surrounding tissues, very short pulse widths (shorter than the target thermal relaxation time) are used to heat and ablate the ink faster than heat is conducted to the surrounding tissue.

• Spot size (measured in millimeters) is the diameter of the laser beam on the skin surface. Use of a larger spot size results in less scatter of the photons and deeper laser beam penetration. This maximizes the distribution of laser light to the dermal ink and reduces epidermal injury. Larger spot sizes should be used as long as sufficient fluence can be obtained to achieve the desired clinical endpoint. A smaller spot size (e.g., 2 to 3 mm) has greater scattering of photons, delivers energy less efficiently, and causes more epidermal injury than larger spot sizes (e.g., 6 to 8 mm).

• Wavelength (measured in nanometers) is chosen based on the tattoo ink color. In general, as the wavelength increases, so does the depth of penetration.

• The energy output is known as fluence (measured in joules per square centimeter). More specifically, fluence is defined as the amount of energy delivered per unit area. Fluence should be sufficient to produce immediate whitening with tattoo treatment without bleeding or blistering. The fluence emitted with a given spot size is dependent on the device used. Adequately powered tattoo laser devices can maintain high fluences (e.g., more than 4.5 J/cm²) with large spot sizes (e.g., 6 mm).

Patient and Tattoo Selection

Lasers may be used for tattoo removal in patients of all skin types (Fitzpatrick types I through VI). However, patients with darker skin types (IV through VI) are at greater risk for side effects, specifically hypopigmentation and hyperpigmentation. Topical hydroquinone (2% to 8%) can be used preprocedure, and resumed once the skin is healed postprocedure, to reduce the risk of postinflammatory hyperpigmentation in patients with darker skin types. Additionally, patients of Asian or African descent have a greater predisposition to hypertrophic and keloidal scarring. In general, Fitzpatrick skin type VI patients have the greatest risk of complications with any aesthetic procedure, and providers should consider treatment of this skin type an advanced laser application.

Almost any tattoo is indicated for laser tattoo removal. Multiple treatments are needed to achieve satisfactory results. Due to great variation in tattoo ink depth, density, composition, and techniques used for placement, the number of treatments needed for removal can be difficult to estimate accurately. In general, professionally placed tattoos have a high ink density and require 9 to 14 treatments, whereas amateur tattoos typically require 4 to 8 treatments. Several other factors can affect the number of treatments necessary for removal: faded, older tattoos on paler skin types in more proximal locations tend to resolve with fewer treatments than intense, multicolored tattoos on darker skin types in distal locations.⁶ Patients should be questioned about other tattoo removal methods used previously. Methods that create scar tissue, such as burning or abrasion, can make tattoo removal with lasers less successful.

Certain types of tattoos are considered advanced, and treatment should not be undertaken until the provider is fully confident in his or her skill with artistic tattoo removal. Advanced tattoos include cosmetic tattoos, such as those used for permanent eyeliner or lip liner, flesh-colored inks, and traumatic tattoos.

Indications

Laser tattoo removal is indicated for the treatment of ectopic skin pigment. This pigment is usually from purposefully placed ink in tattoos (both professional and amateur artistic tattoos) as well as tattoos associated with medical procedures (e.g., radiation therapy tattoos). In rare cases ectopic pigment may be the result of trauma (traumatic tattoos) where materials such as asphalt are trapped in the dermis.

Alternative Therapies

The following alternatives to Q-switched laser tattoo removal methods are not recommended:

• Dermabrasion (not to be confused with microdermabrasion)

• Salabrasion

• Cryotherapy (liquid nitrogen)

• Continuous-wave lasers

• Chemical acids

• Thermal injury (electrocautery).

The results of using these alternative modalities are often unsatisfactory to both patients and health care professionals. These techniques significantly increase the risk of adverse effects including scarring, hypopigmentation, hyperpigmentation, depigmentation, incomplete resolution of ink, pain, prolonged healing time, infection, textural changes, and unpredictable outcomes. The advantage of these techniques is that they are relatively inexpensive and may offer faster ink resolution when compared to laser tattoo removal treatments. Some providers use surgical excision as a method of tattoo removal.

Products Currently Available

Q-switched lasers are now widely regarded as the gold standard for laser tattoo removal. Current Q-switched lasers available include:

• Q-switched Nd:YAG laser (1064 nm)

• Frequency doubled (532 nm)

• Dye modules (650 nm and 585 nm)

• Q-switched alexandrite laser (755 nm)

• Q-switched ruby laser (694 nm).

The Q-switched Nd:YAG (neodymium-doped yttrium aluminum garnet) produces a 1064 nm wavelength of light that is ideal for treating black ink. A primary disadvantage is its limited efficacy in removing yellow and green inks. With some devices, through a process called frequency doubling, an Nd:YAG laser can also produce light with a wavelength of 532 nm to treat red, orange, and yellow inks.²⁰ The Nd:YAG laser has an advantage of treating darker skinned patients with less risk of hypopigmentation, hyperpigmentation, and textural changes.⁷ This can be attributed to the increased dermal penetration of this longer wavelength and the lower melanin absorption. The wavelength of the light emitted by the Q-switched alexandrite laser is 755 nm. This wavelength has excellent absorption by black, good absorption by green and blue, but poor absorption by red ink. The ruby laser was one of the first Q-switched lasers, and it emits a 694 nm wavelength. It works well for darker colors (black, blue-black, and some green), but poorly on yellow and red ink. Although more effective for green ink than the Nd:YAG, the ruby laser commonly causes hypopigmentation and hyperpigmentation and, although usually transient, may be permanent.⁵

Recently, a number of lower cost, Q-switched devices have become available. Although considerably less expensive, these units have little to no long-term track records and are of unknown quality. Choosing a device with a more established company is recommended.