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Premature Aging Takes the Heat with Infrared

Infrared A radiation increased levels of the collagen-degrading enzyme MMP-1 and depleted cutaneous antioxidents.

Excessive exposure to sunlight ages skin prematurely. Although researchers have attributed the harm primarily to UVA and UVB radiation, sunlight includes wavelengths outside the UV spectrum. In fact, approximately 30% of all solar energy that reaches the earth’s surface lies within the infrared A (IRA) range (760–1440 nm). To determine whether infrared A contributes to photoaging, investigators exposed 23 volunteers to 360 or 720 J/cm² IRA, levels that can be reached with a few hours of sun exposure in temperate climates.

In approximately 80% of the volunteers, these doses produced 3-fold to 14-fold increases in matrix metalloproteinase-1 (MMP-1), an enzyme that degrades elastin and types I and III collagen. The effect of infrared A on MMP-1 occurred primarily in the dermis, regardless of age, sex, and skin type. By contrast, infrared A had no effect on the tissue inhibitor of MMP-1 (TIMP-1), which counteracts MMP-1 activity. Previous in vitro studies showed an oxidative stress response in fibroblasts exposed to IRA. Consistent with this observation, when volunteers underwent IRA exposure, a transient depletion of antioxidants in the skin was evident. Topical application of a mixture of antioxidants (including grape seed extract, ubiquinone, vitamin C, and vitamin E) inhibited the increase in MMP-1 mRNA expression.

Comment: Additional studies are still needed to establish that an increase in infrared A-induced enzyme level corresponds to increased collagen and elastin degradation. Assuming that this is so, these provocative findings demonstrate that skin photoaging is not restricted to the UVA and UVB spectra. For the practicing dermatologist, this finding means that preventing photoaging is even more difficult than we thought, as sunscreens presumably do nothing to diminish the effects of IRA. These results highlight the need for new photoprotective agents with novel modes of action and scientifically proven antioxidant activity on the skin. Until such agents have been identified, clinicians should recommend that patients use sun avoidance and photoprotective clothing in addition to sunscreens.

— Craig A. Elmets, MD

Published in Journal Watch Dermatology October 17, 2008

Citation(s):

Schroeder P et al. Infrared radiation-induced matrix metalloproteinase in human skin: Implications for protection. J Invest Dermatol 2008 Oct; 128:2491.

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