Skin Resurfacing

Introduction

Facial aging is complex and occurs at all tissue levels, from the underlying skeletal scaffolding, through the musculature, adipose tissue, and skin. Advances in aesthetic medicine now allow us to not only recognize specific changes in these tissue layers, but also address and in some cases correct the clinical signs of aging at its respective anatomic site.

The skin ages through two main processes: intrinsic and extrinsic aging. Intrinsic aging is the result of genetic background and chronology. It is an inevitable consequence of aging seen in all anatomic locations of skin regardless of exposure to ultraviolet (UV) light. Changes characteristic of intrinsic aging include decreased elasticity, decreased skin turgor, and loss of hair. On histology, the skin demonstrates flattened rete ridges and dermal atrophy . Extrinsic aging of the skin is the result of external factors such as UV exposure, alcohol use, tobacco use, and nutrition. These are largely controllable factors and therefore extrinsic aging is not necessarily inevitable. UV exposure is the primary driver of extrinsic aging, with some estimates attributing over 80% of facial skin aging to the sun . Extrinsically aged skin appears primarily in sun-exposed areas such as the face, neck, chest, and extensor arms, and is often referred to as “photo­aging”. Clinically it appears as rhytids, dyschromia, lentigines, loss of elasticity, skin fragility, telangiectasias, and purpura. In more severe cases actinic keratoses and skin cancer begin to develop.

Aging of the skin, particularly that of photoaging, is readily apparent to both patient and practitioner and a common reason to visit a cosmetic physician. Because the pathologic process of photoaging is primarily limited to the epidermis and upper dermis, it is readily amenable to treatment with a wide variety of lasers and light sources. In 2014, over a half a million laser skin resurfacing procedures were performed in the United States, a 218% increase from 2000 . The remainder of this chapter will address the use of lasers to resurface the skin and treat signs of aging. The focus of this chapter is to review the principles and clinical applications of lasers in the treatment of aging skin. A full understanding of the physical properties of lasers used in medicine allows the practitioner to best adjust the settings to each patient and clinical application.

Laser Principles

The word laser is an acronym for L ight A mplification by S timulated E mission of R adiation. Lasers contain four key components: (1) an excitable medium; (2) an energy source; (3) mirrors forming an optical cavity; and (4) a delivery system. When energy is applied to the lasing medium, photons are emitted that stimulate further photon emission equal in energy and wavelength. This results in the emission of photons that are in phase both temporally and spatially; thus, the light emitted by a laser is one single wavelength, or monochromatic. This is a key attribute of lasers and why devices that emit a range of wavelengths, like intense pulsed light, are not lasers but should be referred to as light sources. Emitted light from lasers is completely in phase, meaning all peaks and troughs of the wave are in line. Thus, the light is termed coherent. This property allows the laser to be focused to a spot size as small as the wavelength itself. Additionally, the beam of light from a laser is collimated, meaning it travels in a parallel, nondivergent path unlike that of traditional light sources