Up to this point, the types of lasers, their use in treatment of skin conditions, and the presumed mechanism/mode of action have been described. The remainder of this chapter will review the toxicological or adverse events associated with the laser treatments of nonablative dermatological conditions. Considering the mechanism/mode of action of lasers with wavelengths between visible and near IR (500-1300 nm), the areas of toxicological concern include: (i) primary effects such as photon absorption by a chromophore, and the dissipation of energy as heat and potential photochemical conversion of endogenous chromophore to a new chemical entity; (ii) secondary events such as inhibition/stimulation of biomolecules, that is, inhibition of cytochrome enzyme and formation of free radicals; and (iii) events associated with the procedure including exposure to tissue debris, fumes, etc. and the safety of the laser device, that is, electrical/device failure, that is, fire. The focus will be on the primary and secondary events at the site of treatment or exposure. Significantly, systemic toxicity is not considered to be of concern, given the localized effects of laser light in the skin or underlying fat.
Of all potential concerns at the site of exposure, the prominent one is thermal events. In general, the longer wavelength visible and infrared lasers are used at fluences incapable of promoting the majority of biomolecules to electronically excited states and, as such, photochemical conversions such as isomerization, breaking bonds, or formation of photoproducts are not observed. Infrared radiation is absorbed, and produces vibrational energy that may cause thermal damage to the target and, if there is sufficient energy, to the surrounding tissue. Thermal effects are considered in the context of acute and chronic toxicity, with special attention given to reversibility. Secondary toxicities and idiosyncratic responses are reviewed as well. Handley [106] provides an excellent review of adverse events associated with nonablative cutaneous laser treatment.