Photoprotection
Ultraviolet (UV) radiation consists of UVC (270–290 nanometers [nm]), ultraviolet B (UVB) (290–320 nm) and ultraviolet A (UVA), which is further classified into UVA1 (340–400 nm) and UVA2 (320–340 nm). UVC radiation does not reach the surface of the earth
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Photoprotection Camile L. Hexsel and Henry W. Lim
Author contributions: Dr. Lim and Dr. Hexsel have participated in the conception and design, drafting and critical revision of the chapter for important intellectual content. Conflict of interest: Dr. Lim is a consultant for La Roche-Posay, Orfagen, Johnson and Johnson, and Dow Pharmaceuticals; and he has received research grant support from Johnson and Johnson. Dr. Hexsel has no conflicts of interest to declare.
9.1 Cutaneous Effects of Ultraviolet Radiation Ultraviolet (UV) radiation consists of UVC (270–290 nanometers [nm]), ultraviolet B (UVB) (290–320 nm) and ultraviolet A (UVA), which is further classified into UVA1 (340–400 nm) and UVA2 (320–340 nm). UVC radiation does not reach the surface of the earth as it is filtered by the ozone layer. On the surface of the earth, there is 20 times more UVA than UVB. Cutaneous effects of UV radiation can be divided into acute and chronic. Acute effects include erythema, edema, blisters, and immediate and delayed pigment darkening followed by tanning or neomelanogenesis, acanthosis, and dermal thickening. Exposure to UV can also induce immunosuppression, vitamin D synthesis, and development of photodermatoses. Erythema and edema are primarily induced by UVB, start at 3–4 h after UVB exposure, and peak at
C. L. Hexsel (*) Department of Dermatology, Henry Ford Hospital, Detroit, MI, USA e-mail: [email protected]
8–24 h. They last 24–48 h or longer in light-skinned individuals. Delayed tanning or neomelanogenesis peaks at 72 h after UV radiation. UVB-induced delayed tanning requires a preceding erythemal response and has a sun protection factor (SPF) of 3. In contrast to UVB, UVA-induced erythema peaks at 1–2 h after exposure and subsides gradually over 24–72 h. Because of the longer wavelength of UVA, it takes 1,000-fold more fluence (dose) to induce erythema by UVA compared to UVB. UVA also induces immediate and delayed pigment darkening followed by tanning. Immediate pigment darkening (IPD) occurs within seconds after UVA and visible light irradiation, and resolves in 2 h; it is due to photo-oxidation of preexisting melanin.1 Persistent pigment darkening (PPD) is also a result of a photo-oxidation and redistribution of preexisting melanin; PPD persists from 2 to 24 h after irradiation.1, 2 UVA-induced delayed tanning, which is secondary to neomelanogenesis, appears usually 3 days after exposure.1 Chronic effects of UV radiation include photoaging and the development of actinic keratosis, basal cell carcinoma, and squamous cell carcimona.1, 3, 4 Melanoma has been associated with intermittent intense acute sun exposure and history of sunburns. The specific wavelengths associated with melanoma have not completely been identified; therefore, although sunburns are associated with an increased risk of melanoma, the specific wavelengths of UV responsible for sunburn may not be the same wavelengths responsible for the development of melanoma.3 Although solar radiation comprises a broad range of wavelengths, several eye di
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