Ultra-long UVA: an insidious enemy of the skin

ULTRA-LONG UVA RAYS* (380 TO 400 NANOMETERS) AMOUNT TO 30% OF TOTAL UV RAYS REACHING OUR SKIN.
ULTRA-LONG UVAs PENETRATE THE SKIN DEEPLY, CAUSING LONG-TERM DAMAGES ON SKIN CELLS, DNA AND THE IMMUNE SYSTEM. UP TO THIS DAY, NO SOLAR FILTER WAS COVERING THESE UVA RAYS EFFICIENTLY.
WITH MEXORYL 400, LA ROCHE-POSAY DEVELOPED THE FIRST SOLAR FILTER PROTECTING SKIN FROM ULTRA-LONG UVAs AND THEIR DAMAGES. THIS SCIENTIFIC REVIEW EXPLORES THE LATEST DERMATOLOGICAL KNOWLEDGE ABOUT UVB, UVA AND LONG UVA DAMAGES ON SKIN CELLS, DNA AND THE IMMUNE SYSTEM.
*[380-400nm] = Long-UVA/ [380-400nm] =end of the spectrum that we call ultra-long UVA.

AN INSIDIOUS DANGER

While UVB rays cause rapid damages on skin (i.e.: sunburns…), recent research reveals that ultra-long UVAs cause more severe damages on the mid and long terms, as they penetrate the skin deeper than UVB rays. These damages don’t show instantly but appear progressively.

Sources: Angela Tewari, UVA1 in skin deep: molecular and clinical implications. Photochem Photobiol Sci. 2013 Jan;12(1):95-103.

CELL DAMAGES AND IMMUNOSUPPRESSION

Under ultra-long UVA irradiation, oxidative stress contributes to DNA damages in skin cells such as fibroblasts, melanocytes and keratinocytes. Lymphocytes are also impacted, thus leading to skin immunity losses. UVA rays are already known for being responsible of 75% of immunosuppression resulting from sun exposure. Recent research suggests that, among them, ultra-long UVA rays are likely to be the largest contributors to immunosuppression.

Sources: Gary M Halliday, Ultraviolet A radiation: its role in immunosuppression and carcinogenesis. Semin Cutan Med Surg. 2011 Dec;30(4):214-21 ; Jean-Claude Beani, [Ultraviolet A-induced DNA damage: role in skin cancer].Bull Acad Natl Med. 2014 Feb;198(2):273-95. ; Marionnet, C., et al., Diversity of biological effects induced by longwave UVA rays (UVA1) in reconstructed skin. PLoS One, 2014. 9(8): p. e105263. ; D L Damian, An action spectrum for ultraviolet radiation-induced immunosuppression in humans. Br J Dermatol. 2011 Mar;164(3):657-9.

IMPACTS ON SKIN CANCER

Skin cancers arise from cells present in basal skin layers. Thus, DNA lesions caused by ultra-long UVAs accelerate skin carcinogenesis. Ultra-long UVA rays have a specific ability to generate cyclobutane pyrimidine dimers (CPD), that are implicated in many aspects of skin cancers.

Sources: Tewari A et al, UVA1 induces cyclobutane pyrimidine dimers but not 6-4 photoproducts in human skin in vivo. J Invest Dermatol. 2012;132(2):394-400. ; Angela Tewari, UVA1 in skin deep: molecular and clinical implications. Photochem Photobiol Sci. 2013 Jan;12(1):95-103.