Dermal damage promoted by repeated low-level UV-A1 exposure despite tanning response in human skin

Frank Wang, Noah R. Smith, Bao Anh Patrick Tran, Sewon Kang, John J. Voorhees, Gary J. Fisher

Research output: Contribution to journalArticlepeer-review

Abstract

IMPORTANCE Solar UV irradiation causes photoaging, characterized by fragmentation and reduced production of type I collagen fibrils that provide strength to skin. Exposure to UV-B irradiation (280-320 nm) causes these changes by inducing matrix metalloproteinase 1 and suppressing type I collagen synthesis. The role of UV-A irradiation (320-400 nm) in promoting similar molecular alterations is less clear yet important to consider because it is 10 to 100 times more abundant in natural sunlight than UV-B irradiation and penetrates deeper into the dermis than UV-B irradiation. Most (approximately 75%) of solar UV-A irradiation is composed of UV-A1 irradiation (340-400 nm), which is also the primary component of tanning beds. OBJECTIVE To evaluate the effects of low levels of UV-A1 irradiation, as might be encountered in daily life, on expression of matrix metalloproteinase 1 and type I procollagen (the precursor of type I collagen). DESIGN, SETTING, AND PARTICIPANTS In vivo biochemical analyses were conducted after UV-A1 irradiation of normal human skin at an academic referral center. Participants included 22 healthy individuals without skin disease. MAIN OUTCOMES AND MEASURES Skin pigmentation was measured by a color meter (chromometer) under the L variable (luminescence), which ranges from 0 (black) to 100 (white). Gene expression in skin samples was assessed by real-time polymerase chain reaction. RESULTS Lightly pigmented human skin (L* >65) was exposed up to 4 times (1 exposure/d) to UV-A1 irradiation at a low dose (20 J/cm 2 ), mimicking UV-A levels from strong sun exposure lasting approximately 2 hours. A single exposure to low-dose UV-A1 irradiation darkened skin slightly and did not alter matrix metalloproteinase 1 or type I procollagen gene expression. With repeated low-dose UV-A1 irradiation, skin darkened incrementally with each exposure. Despite this darkening, 2 or more exposures to low-dose UV-A1 irradiation significantly induced matrix metalloproteinase 1 gene expression, which increased progressively with successive exposures. Repeated UV-A1 exposures did not suppress type I procollagen expression. CONCLUSIONS AND RELEVANCE A limited number of low-dose UV-A1 exposures, as commonly experienced in daily life, potentially promotes photoaging by affecting breakdown, rather than synthesis, of collagen. Progressive skin darkening in response to repeated low-dose UV-A1 exposures in lightly pigmented individuals does not prevent UV-A1-induced collagenolytic changes. Therefore, for optimal protection against skin damage, sunscreen formulations should filter all UV wavelengths, including UV-A1 irradiation.

Original languageEnglish (US)
Pages (from-to)401-406
Number of pages6
JournalJAMA Dermatology
Volume150
Issue number4
DOIs
StatePublished - Apr 2014

ASJC Scopus subject areas

  • Dermatology

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