The skin is the biggest organ of the body, representing its barrier to the environment. It provides protection against water loss, keeps microorganisms from invading our body, and responds sensitively to external stimuli. The skin barrier is formed by the uppermost cell layer, i.e., the stratum corneum, consisting of dead horny cells. Underlying the stratum corneum are various layers of living cells. The capillary structures of the blood vessels appear from a depth of approximately 150 µm beneath the skin surface. The homogeneous structure of the skin surface is interrupted by hair follicles and sweat glands. As a sensory organ the skin is an essential means of interpersonal communication. This is why we devote particular attention to skin care and dermal treatment. In this context, diagnostics and therapy control play a decisive role. Easily accessible, the skin is an ideal object to be investigated by noninvasive optical and spectroscopic methods. An ample range of such methods is available for dermal analysis, including fluorescence, reflectance, Raman, and CARS measurements. Laser scanning microscopy has proven to be specifically suitable for investigating the skin barrier and the underlying living cell layers up to a depth of 200 µm depending on the wavelength applied, imaging both cellular and molecular structures. The primary purpose of these investigations is to analyze the integrity of the skin barrier, which is characterized by the organization of the cellular structures and by the composition of the lipid layers surrounding the cells. The application both of laser scanning microscopy and optical coherence tomography is focused mainly on the detection of dermal lesions, in particular of skin tumors, and their response to different therapies.

Optical imaging methods are also becoming increasingly popular in the field of pharmacology, specifically for investigating the penetration of topically applied substances into and through the skin barrier.

Due to the rapid development of optical techniques, both in terms of excitation by lasers and light-emitting diodes, and in terms of detection using capacitive sensors, optical and spectroscopic methods are increasingly applied in medicine, cosmetics, and cutaneous physiology. The articles published in this special section provide some impressive examples.

In this special section, 31 papers describe the broad application of optical methods for skin imaging. Laser scanning microscopy and multiphoton tomography are often used techniques in skin research and clinical diagnostics [, J. Biomed. Opt. 18(6), 061207Guojin et al.; , J. Biomed. Opt. 18(6), 061211Ulrich et al.; J. Biomed. Opt. 18(6), 061229; , J. Biomed. Opt. 18(6), 061216Hoffman et al.; , J. Biomed. Opt. 18(6), 061217Sanchez et al.; , J. Biomed. Opt. 18(6), 061227Abeytunge et al.; , J. Biomed. Opt. 18(6), 061231Tanaka et al.; and , J. Biomed. Opt. 18(6), 061225Lai et al.].

Several papers are related to the application of Raman spectroscopy for the analysis of human skin tissue [, J. Biomed. Opt. 18(6), 061202Syed et al.; , J. Biomed. Opt. 18(6), 061210Franzen et al.; , J. Biomed. Opt. 18(6), 061230Darvin et al.] and of nickel allergy [, J. Biomed. Opt. 18(6), 061206Alda et al.].

The application of optical coherence tomography in dermatology is discussed by , J. Biomed. Opt. 18(6), 061213Liew et al. and , J. Biomed. Opt. 18(6), 061224Sattler et al.. The application of optical methods permits distinguishing between different types of skin cancer and is helpful for therapy planning [, J. Biomed. Opt. 18(6), 061208Darlenski et al.; , J. Biomed. Opt. 18(6), 061211Tchvialeva et al.; and , J. Biomed. Opt. 18(6), 061221Drakaki et al.].

Optical methods are also applied for blood flow imaging [, J. Biomed. Opt. 18(6), 061204Sun et al.; , J. Biomed. Opt. 18(6), 061209Wang et al.; , J. Biomed. Opt. 18(6), 061219Klein et al.; and , J. Biomed. Opt. 18(6), 061220Nishidate et al.] and for the analysis of wound healing processes [, J. Biomed. Opt. 18(6), 061202Pesqueira et al.; , J. Biomed. Opt. 18(6), 061204Medina-Preciado et al.; and , J. Biomed. Opt. 18(6), 061222Deka et al.].

The interaction of nanoparticles with human skin is a topic of increasing interest. Research into this specific field using optical imaging methods is presented by , J. Biomed. Opt. 18(6), 061207Yu et al.; , J. Biomed. Opt. 18(6), 061214Zhang et al.; , J. Biomed. Opt. 18(6), 061215Song et al.; , J. Biomed. Opt. 18(6), 061218Labouta et al.; and , J. Biomed. Opt. 18(6), 061226Fixler et al..

Very often model calculation of skin physiological processes are based on results obtained by optical imaging techniques [, J. Biomed. Opt. 18(6), 061232Okamoto et al.; , J. Biomed. Opt. 18(6), 061228Liu et al.; and , J. Biomed. Opt. 18(6), 061223Terstappen et al.].

It will also be shown that a single technique suitable for all issues is not available, but that it is necessary to select the optimum technique for the specific purpose.