Unlike previous treatment modalities for pig-mented lesions, Q-switched lasers induce minimal side effects. These include pigmentary changes, partial removal, infection, bleeding, textural changes, and tattoo ink darkening.
Pigmentary changes following laser treatment of pigmented lesions are not uncommon. Transient hypopigmentation is most common after treatment with the 694- or 755-nm wavelengths because absorption by melanin is so strong. Permanent hypopigmentation can be seen with repetitive treatment sessions, particularly at higher fluences. The 1064-nm wave length is the least injurious to melanocytes and is therefore the treatment of choice for dark-skinned individuals undergoing laser tattoo treatment. Transient hyperpigmentation, which has been reported in up to 15% of cases, is more common in darker skin types or following sun exposure (Kilmer et al. 1993). The incidence of scarring is less than 5%. It is associated with the use of excessive fluences. It is also more common when certain areas like the chest and ankle are treated. This complication has also been observed in areas with dense deposition of ink, such as in double tattoos. Larger laser spot sizes tend to minimize epidermal damage and are associated with fewer textural changes.
Pigment darkening of cosmetic skin color tattoos can occur after exposure to any Q-switched laser. The darkening occurs immediately and is most often seen with the red, white, or flesh-toned ink colors that are frequently used in cosmetic tattoos. These colors often contain ferric oxide and titanium dioxide that can change to a blue-black color after Q-switched laser treatment. The mechanism probably involves, at least for some tattoos, reduction of ferric oxide (Fe2O3, "rust") to ferrous oxide (FeO, jet black). Recently, multiple color changes following laser therapy of cosmetic tattoos has been reported (Fig. 3.11). Performing small test areas before complete treatment and using several laser wavelengths throughout the course of therapy are essential to the successful treatment of cosmetic tattoos.
Localized allergic reactions can occur with almost any treated tattoo color. It can result in an immediate hypersensitivity reaction such as urticaria (Ashinoff 1993). In the alternative, a delayed hypersensitivity reaction such as granuloma formation may occur. The most serious complication reported after Q-switched laser tattoo removal was a systemic allergic reaction. The Q-switched laser targets intracellular tattoo pigment, causing rapid thermal expansion that fragments pigment-containing cells and causes the pigment to become extracellular. This extracellular pigment may then be recognized by the immune system as foreign, potentially triggering an allergic reaction. Therefore, if a patient exhibits a local immediate hypersensitivity reaction, prophylaxis before subsequent laser treatments with systemic antihistamines and steroids should be considered. Pulsed CO2 and erbium lasers do not seem to trigger this reaction, since the particle size does not change. These lasers may be used to enhance transepi-dermal elimination of ink.
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