Visible light and skin health: mechanisms of damage and photoprotection

Visible light (VL, 400–700 nm) and long-wavelength ultraviolet A1 (UVA1, 370–400 nm) significantly impact human skin, inducing pigmentation, oxidative stress, inflammation and exacerbation of existing pigmentary disorders. These effects present challenges for photoprotection, as traditional sunscreens inadequately shield against these wavelengths. This thesis explores the biological effects of VL and UVA1 on skin and evaluates novel photoprotection strategies, including antioxidant-enriched formulations and tinted sunscreens.

Inspired by the initial work by Kollias et al [1], a series of studies investigated the dose-response relationship between VL/UVA1 exposure and pigmentation in individuals with diverse skin phototypes. The first study described in this work Mahmoud et at [2] showed that VL can induce more pigmentation in subjects with dark skin phototypes than UVA1 radiation. Further studies demonstrated that VL induces persistent pigmentation and melanogenesis through photoadaptive pathways [3]. In darker skin phototypes, exposure to VL resulted in intense and sustained pigmentation, characterized by activation of melanogenic pathways and increased tyrosinase activity. This pigmentation often persisted for weeks, exacerbating conditions like post-inflammatory hyperpigmentation and melasma. Additionally, darker skin exhibited a heightened oxidative stress response to VL and UVA1 exposure, emphasizing the need for targeted photoprotection strategies that address these unique vulnerabilities.

Light-skinned individuals [4] were found to experience transient erythema and delayed tanning with repeated exposures. While less pronounced than in darker skin, these responses highlight the susceptibility of light skin to VL-induced damage, including oxidative stress and inflammation. These findings underscore that VL effects are not exclusive to darker skin and that effective protection is crucial across all skin types.

The first fundamental study investigating the mitigation of visible light-induced effects on the skin was conducted by Liebel et al. [5], demonstrating that Feverfew (Tanacetum parthenium) extract, Soy (Glycine soja) extract, and Gamma-Tocopherol effectively neutralized visible light-induced reactive oxygen species (ROS) in vitro and in vivo by chemiluminescence. This study was pivotal in identifying antioxidants as a potential strategy to counteract visible light-induced oxidative stress; however, it was not designed to demonstrate any effect on mitigating pigmentation or erythema.

Subsequent studies expanded on this approach by formulating and testing blends of antioxidants, including Diethylhexyl Syringylidene Malonate (Oxynex ST®), Glycyrrhetinic Acid, Licochalcone A, Vitamin C, and Vitamin E [5, 6, 7, 8]. These formulations showed significant clinical relevance in reducing both pigmentation and erythema in individuals with varying skin phototypes.

Another strategy to protect skin against VL was to design formulations containing correct attenuation [9] of high energy visible light (HEV- 400-450 nm spectral range) by using the yellow iron oxide and other pigments (black/red iron oxide and pigmentary titanium dioxide) to match skin tone. These findings highlighted the potential of incorporating such agents into comprehensive photoprotection regimens.

This research advances understanding of VL and UVA1’s effects on skin and offers insights into innovative photoprotection strategies. Future work should refine these formulations and establish standardized methods for evaluating their efficacy, addressing a critical gap in dermatological care.