Overview of cutaneous photosensitivity: Photobiology, patient evaluation, and photoprotection
- Craig A Elmets, MD
Craig A Elmets, MD
- Section Editor — Photodermatology
- Professor and Chair of Dermatology
- University of Alabama at Birmingham
- Section Editors
- Robert P Dellavalle, MD, PhD, MSPH
Robert P Dellavalle, MD, PhD, MSPH
- Section Editor — Dermatology
- Professor of Dermatology and Public Health
- University of Colorado School of Medicine
- Colorado School of Public Health
- Chief, Dermatology Service
- US Department of Veterans Affairs
- Eastern Colorado Health Care System
- Jeffrey Callen, MD, FACP, FAAD
Jeffrey Callen, MD, FACP, FAAD
- Editor-in-Chief — Dermatology
- Section Editor — Skin and Systemic Disease
- Professor of Medicine
- University of Louisville School of Medicine
Photosensitivity is an abnormal cutaneous response to ultraviolet radiation (UVR) and, in some individuals, visible light. Depending upon the type of photosensitivity disease, the abnormal response can manifest as macular erythema, papules, plaques, vesicles, bullae, telangiectasias, or eczematous patches. For some photosensitivity diseases, the rash may result in scarring. One of the key features in establishing the diagnosis of a photosensitive eruption is its distribution. In most instances, it occurs on sun-exposed areas of the skin; the face, ears, dorsal forearms, "V"-area of the neck, and upper chest are commonly affected sites. However, occasionally it can occur on covered areas of the body, especially in individuals who use tanning beds.
The principles of photobiology, evaluation of the photosensitive patient, and general recommendations for photoprotection in the photosensitive patient will be reviewed here. The diagnosis and treatment of specific photosensitivity conditions and sunburn are discussed separately. (See "Photosensitivity disorders (photodermatoses): Clinical manifestations, diagnosis, and treatment" and "Polymorphous light eruption" and "Sunburn".)
Ultraviolet radiation (UVR) emitted from the sun is divided into three wavelength ranges: UVA (320 to 400 nm), UVB (290 to 320 nm), and UVC (200 to 290 nm). UVC is absorbed by the ozone layer in the atmosphere . Because of this, UVC does not reach the earth's surface and usually does not play a role in inducing photosensitivity. However, it is emitted by germicidal lamps and welding arcs and has been rarely reported to provoke photosensitivity in individuals with occupational exposure. UVA and some UVB penetrate the atmosphere and reach the earth's surface.
Patients with photosensitivity may react to UVA, UVB, or visible light (400 to 760 nm) (figure 1). Longer wavelengths penetrate deeper into the skin. UVA passes through the epidermis and into the dermis, whereas UVB enters into the epidermis, but little reaches the dermis. UVR has multiple effects on the skin. Notably, UVR causes DNA damage and mutations, which are initiating events in skin carcinogenesis. UV-induced immunosuppression may also contribute to the development of skin cancers by interfering with the ability of the immune system to identify and eliminate neoplastic cells before they become clinically apparent skin cancers. A further effect of UVR is the generation of reactive oxygen species, such as singlet oxygen, superoxide anion and hydrogen peroxide. The generation of reactive oxygen species leads, among other things, to lipid peroxidation, DNA damage, and activation of signal transduction pathways. These effects have been implicated in the pathogenesis of skin cancer, photoaging, and inflammatory responses in photosensitivity disorders.
EVALUATION OF PATIENTS WITH PHOTOSENSITIVITY DISORDERS
Photosensitivity disorders of the skin are conditions in which an abnormal cutaneous response occurs after exposure to ultraviolet radiation or visible light. The major categories include idiopathic photodermatoses, photodermatoses due to exogenous or endogenous agents, photoexacerbated dermatoses, and photosensitive genodermatoses.
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