Impact of Iron-Oxide Containing Formulations Against Visible Light-Induced Skin Pigmentation in Skin of Color Individuals

July 2020 | Volume 19 | Issue 7 | Original Article | 712 | Copyright © July 2020


Published online June 18, 2020

Hawasatu Dumbuya PhDa, Pearl E Grimes MDb, Stephen Lynch PhDa,b, Kalli Ji PhDa, Manisha Brahmachary PhDa, Qian Zheng Md PhDa, Charbel Bouez PhDa, Janet Wangari-Talbot PhDa

aL’Oréal Research and Innovation, Clark, NJ bVitiligo & Pigmentation Institute, Los Angeles, CA

Abstract
Visible light (400–700nm), which contributes to 45% of solar radiation, contributes to skin darkening and worsening of dyschromias, particularly in individuals with Fitzpatrick skin phototypes III and higher. Currently, sunscreens provide limited protection against that spectrum. Due to their capabilities in absorbing, scattering, and reflecting visible light, topical products containing pigments and/or metal oxides can provide additional photoprotection. In this study, the efficacy of two formulations containing iron oxide was evaluated in preventing visible light-induced pigmentation compared with a non-tinted mineral SPF 50+ sunscreen. Expert grading and colorimetry demonstrated that the iron-oxide containing formulations significantly protected against visible light-induced pigmentation compared to untreated skin or mineral SPF 50+ sunscreen in Fitzpatrick IV individuals. These results highlight that iron-oxide containing formulas in a foundation format have dual functions and can provide additional benefits in patients’ daily routine by masking existing pigmentation and preventing the development of pigmentation triggered by sunlight exposure, extending protection beyond UV spectrum.

J Drugs Dermatol. 2020;19(7): doi:10.36849/JDD.2020.5032

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INTRODUCTION

At the earth’s surface, solar radiation comprises of 5–7% ultraviolet (UV), 45% visible light (VIS), and 48–50% infrared (IR) radiation.1 Studies on the cutaneous impact of radiation have focused on UVB and UVA-mediated effects on the skin. Through different mechanisms, both UVA and UVB are shown to contribute to erythema, tanning, photoaging, and skin cancers.2

In recent years, VIS (400–700nm) was demonstrated to induce both immediate and persistent pigment darkening in subjects with skin phototype III and above.3-5 It has been shown that long wavelength UVA1 (LUVA1) combined with VIS can result in erythema in skin phototype I–III, plus darker, persistent pigmentation and inflammation in subjects with skin phototype IV–VI.6-8 Various protocols consisting of single or multiple exposures have been published to investigate the mechanism of VIS-induced skin darkening.3-9 Growing evidence indicates that pigment formed at earlier time points after VIS irradiation is photo-oxidized melanin while, at later time points, new pigments are synthesized through neo-melanogenesis.5 The proposed molecular mechanism for VIS-induced skin pigmentation is through the activation of Opsin 3, a photo-receptor, which mediates the expression and activity of the rate-limiting enzyme, tyrosinase, in melanocytes.10,11 Despite our growing understanding of the impact of VIS on human skin, commercially available sunscreens have a limited ability to extend protection beyond UV. Using a mini-zone back human model, Duteil el al. showed three products containing iron oxide (FeO), titanium dioxide (TiO2), and pigment, provided protection against VIS (400–700nm)-induced pigmentation following 24 hours after a series of four exposures each at a dose of 144 J/cm2.9 Another study has shown that topical application of a silicone in water emulsion containing 4.5% yellow FeO reduced VIS-induced pigmentation when compared to unprotected skin after 4 consecutive exposures of 150 J/cm2.12 Under real life conditions, daily application of a tinted sunscreen was demonstrated to reduce the appearance of cutaneous hyperchromias after 60 days.13 Additionally, broad-spectrum sunscreens containing FeO alone or in combination with TiO2 and ZnO were shown to improve melasma lesions after 8 weeks, and to prevent relapses after 6 months.14,15

Due to their capabilities in absorbing, scattering, and reflecting visible light, topical products containing metal oxides can provide additional protection.16 Using a similar exposure protocol as Duteil el al., we evaluated the efficacy of two tinted formulations containing a combination of FeO and TiO2 in comparison to a non-tinted mineral SPF 50+ sunscreen with ZnO and TiO2 for protection against visible light-induced pigmentation. The