In this chapter I discuss the elements within the skin (chro-mophores) that absorb laser energy as well as the guiding principle behind all cutaneous cosmetic laser treatment (selective photother-molysis). I will recount the history of the use of lasers to improve the skin's appearance. This use significantly predated our understanding of both chromophores and selective photothermolysis.
The skin is the most accessible organ of the human body and is particularly well suited to treatment with lasers. The effect of a particular laser on the skin is determined by optical qualities of skin components such as color or absorption characteristics, and by physical properties of the laser including wavelength, power, and duration of exposure (pulse width). Wavelength determines how far into the skin laser light will penetrate. The power of the laser and the duration of the pulse of laser light determine how much laser energy is imparted to the skin. These variables can be strategically selected and combined to provide a remarkable degree of precision, using the principle of selective photothermolysis. This principle underlies nearly all cosmetic lasers introduced in the past 15 years. New cosmetic lasers include nonsurgical machines, which remove a specific undesired skin component but do not alter overall skin structure, and surgical machines, which safely remove entire layers of skin without damaging the remaining skin but which require a period of healing. Nonsurgical lasers are used—without damaging the skin or changing its appearance in any way—to remove such unwanted skin features as tattoos, pigmented age spots, and birthmarks; vascular lesions including dilated blood vessels and port wine stains; and even excessive hair. The most common surgical cosmetic laser procedure is laser resurfacing, in which sun-damaged, aged superficial skin layers (including the entire epidermis and some of the dermis) are removed in a controlled fashion. Most of the improvement that follows is a result of the skin's remarkable ability to regenerate itself while healing, producing new tissue to replace what was removed by the laser.
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