TESTING
59
Assessment of homogeneity and UV filter skin retention
Vincenzo Nobile – Complife Italia, Italy
Sunscreens are the most popular products used, for more than a century, to protect the skin against the harmful effects of ultraviolet radiation.1
ABSTRACT Although the UV filters
used in sunscreen formulation are highly regulated and undergo rigorous toxicological testing, there are an increasing number of manuscripts reporting their systemic absorption.2-5
Sunscreen products also have
environmental repercussions. In recent years, benzophenone-3 (oxybenzone) and ethylhexyl methoxycinnamate (octinoxate) have been restricted in Palau, Thailand, Philippines and Hawaii due to their harmful effect on the coral reefs.6
Sunscreens represent then both a valid
protection against dangerous effects derived from UV radiation and a concern for humans and the environment. Sunscreen formulators are then facing the challenge of increasing sunscreen performance while decreasing the UV filters’ concentration. The idea of increasing the performance
of sunscreens products and “decreasing” the UV filters is very attractive. Early studies from Sohn and colleagues reported an influence of solvents on the absorbing properties of UV- filters which was shown to be connected to the solvent polarity.7
Sunscreens have been used for more than a century to protect the skin against the harmful effects of ultraviolet radiation. Although the beneficial role of sunscreens in protecting the skin, there is increasing evidence of UV filters’ systemic absorption and environmental repercussions. Sunscreen formulators are now facing the challenge of increasing sunscreen performance while decreasing the UV filter concentration. In a collaborative study with a
customer we evaluated the ability of a raw material in increasing the homogeneity of application and the retention on skin of UV filters. In order to reach this goal, a preliminary study on 6
From a methodological point of view, the assessment of UV filter retention on skin, addresses the need of fast and reliable techniques. Conventional techniques include absorption studies both in vitro and in vivo10 using reconstructed epidermis, skin stripping (ST) and HPLC.10
demonstrated to be effective in improving the SPF and the UVA-PF.8-9
Antioxidants have been also The sunscreen industry should
have, in the near future, the mission to research and develop new molecules with booster effect or increase the protecting effectiveness of UV filters via synergic mechanisms.
A
spectroscopy11 (LSM)12
Fourier transform infrared (FTIR) or laser scanning microscopy
to detect the UV filters. Despite their
reliability, the timing and/or the cost of these techniques could limit the effective routinary screening of sunscreen products. This is the reason why in a collaborative project with a customer we developed a fast and reliable
B
subjects was carried out using two simple and reliable techniques: UV fluorescence emission and the skin stripping technique. The test product demonstrated
a better homogeneity of application (≈50%) and a better retention on skin than the base formula containing only the UV filters. These results were confirmed by the SPF measurement (5.2 points higher than the base cream plus UV filters). UV fluorescence and skin stripping are
a valuable tool to preliminarily assess sunscreen homogeneity of application and retention on skin. Further testing is in progress to standardise the study design.
method to evaluate the retention and the homogeneity of application of the UV filters.
Materials and methods Test products The test product was a raw material named Celus-Bi® Feel (ROELMI HPC srl, Origgio, Italy). Celus-Bi Feel (zea mays starch, polyvinyl alcohol, glycerin) has a medium granulometry spheroidal physical structure. For test purposes the raw material was added to 3.5% concentration to a base formula (aqua, stearic acid, cetearyl alcohol, isononyl isononanoate, chlorophenesin, disodium EDTA, o-cymen-
C
Figure 1: Homogeneity of the distribution of the sunscreen. a) Base cream: no fluorescence emission under Wood Lamp. b) Base cream + UV filters: non-homogeneity of fluorescence emission under UV lamp. c) Base cream + UV filters + test product: fluorescence emission under Wood Lamp is very homogenous.
www.personalcaremagazine.com June 2021 PERSONAL CARE
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