Attempts to reduce the pain associated with laser treatment include application of topical analgesics [191-196]. In February 2007, the Food and Drug Administration (FDA) issued a Public Health Advisory regarding the use of skin products containing numbing ingredients for cosmetic procedures causing life-threatening side effects. These included: lido – caine, tetracaine, benzocaine, and prilocaine in a cream, ointment, or gel for use as topical anesthetics used in conjunction with laser treatment. The FDA concern arose from reports of two deaths attributed to local anesthetics applied over large body surfaces to reduce pain / discomfort associated with laser hair removal. Though the topical application of analgesis/ anesthetics can reduce pain and discomfort associated with laser treatment, such exposure may carry significant health risks, and should be done with caution and under medical supervision.
To better appreciate the toxicological evaluation of lasers, it helps to compare it to the equivalent approach used for a drug/cosmetic. For a topically applied chemical entity, the pharmacokinetics, that is, absorption, distribution, metabolism, and elimination serve as a suitable starting point. A chemical that is absorbed into the skin or general circulation will, most likely distribute to body compartments such as the blood, undergo biotransformation (metabolism), and be eliminated over time. To understand the toxicological implications of this complex ADME process, preclinical studies are needed, where the parent compound along with any metabolites is evaluated. This evaluation includes the site of application for topically administered drugs and systemic endpoints, for example, reproductive toxicity, repeat exposure toxicity, etc. In contrast, with laser light, we are concerned about the toxicological consequences of the energy (i. e., wavelength) at the site of application/treatment or local, but not systemic toxicity. Thus, for any chemical entity, the toxicological concerns are much more complex, given the ADME and local and systemic toxicity. Further, for most drugs/chemicals the mechanism or the mode of action is unknown. In contrast, for nonablative laser treatments, the mechanism of action is known, and the events are predictable, based on this mechanism. This does not mean the toxicological evaluation of laser light is trivial; rather, the specificity of such devices can be evaluated in a more precise manner.
The toxicological consequences of contemporary nonablative laser treatments are related to the production of heat following the absorption of the energy emitted from such devices. The list of common adverse events attributed to the use of lasers, such as erythema, pain, and discomfort, although frequent in occurrence, are not severe. More important, the most common side effects are reversible. There are some events including pigmentary changes which are infrequent events, largely reversible over time, although less predictive than other toxicological events. Finally, the repeated exposure to laser energy does not appear to have toxicological consequences at this point in time.
It has been 40 years since the first compact microwave ovens were introduced to the American kitchen. In the beginning, such devices were large, awkward, and expensive, and there were many health-related concerns including radiation poisoning, blindness, and sterility. However, over time these fears have been replaced by confidence and enjoyment of the benefits of microwave cooking with an estimated 90% of households in the United States having such a device. Though lasers have not yet become household items like microwaves, concerns regarding health-related fears are analogous. Currently, the majority of dermatological practices use some laser/pulsed light devices in treatment. As such, it is not unreasonable to suggest the future of laser devices most probably includes home use for diagnostic and nonmedical/cosmetic benefits. In fact, there is a hand-held hair removal device available for home use that is available in some countries [23].
To summarize, the use of lasers is in its infancy. Nonetheless, based on existing principles of photobiology/phototoxicology, widespread clinical use of lasers, fluence/spectral response and anticipated uses, there is good reason for optimism regarding human safety.