Abstract
In order to afford the required level of broad-spectrum photoprotection against UV-B and UV-A radiation, sunscreens must contain a combination of UV filters. It is important that any interactions between UV filters do not adversely affect their photostability nor the overall photostability of the sunscreen formulation. In this work, we explore the feasibility of using methyl anthranilate (MA) as an alternative to the photo-unstable UV-A filter, avobenzone. From the in vitro studies presented here, we conclude that MA does not provide sufficient UV-A protection on its own but that it is more photostable in formulation than avobenzone. In addition, we found that both octocrylene (OCR) and ethylhexyl methoxycinnamate (EHMC), two commonly used UV-B filters, can stabilize MA through quenching of its triplet states, as previously reported, which has a demonstrable effect in formulation. In contrast with previously reported observations for mixtures of EHMC and avobenzone, we found no evidence of [2+2] photocycloadditions taking place between EHMC and MA. This work demonstrates how a clear insight into the photophysics and photochemistry of UV filters, as well as the interactions between them, can inform formulation design to predict sunscreen performance.
Highlights
The increasing awareness of the damaging effects of excessive sun exposure [1] has led to a rise in demand for skincare products that provide protection against solar radiation, referred to as photoprotection
UV-A radiation presents additional challenges compared to UV-B considering that it penetrates much deeper into the skin, it is approximately 20 times more abundant at the Earth’s surface than UV-B, and it can be transmitted through glass, meaning skin can be exposed to UV-A even when indoors [9]
It is entirely possible that, as is the case with avobenzone, the performance of methyl anthranilate (MA) might be improved by combination with UV-B filters, and as such, its photochemical behavior remains of interest
Summary
The increasing awareness of the damaging effects of excessive sun exposure [1] has led to a rise in demand for skincare products that provide protection against solar radiation, referred to as photoprotection. While the most effective means of photoprotection is to avoid direct sun exposure, by staying indoors or wearing protective clothing, sunscreens remain the public’s preferred method to protect skin against photodamage [2]. Sunscreens are skincare products, usually in the form of lotions or sprays, that contain active ingredients which absorb, reflect, or otherwise block solar radiation before it can reach vulnerable skin cells [3]. UV-B radiation is directly absorbed by DNA and, as such, it leads to photoinduced DNA mutations that are often responsible for skin cancer [6]. The concept of ‘critical wavelength,’ defined as the wavelength at which 90% of the integrated UV absorbance is reached
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