Formulating broad spectrum UV protection products

Sun care products must offer full UV spectral coverage or ‘broad spectrum’ protection to protect against erythema, premature ageing and photocarcinogenesis. Varying combinations of UV filters can be used to meet all of the necessary criteria for UV protection products; high SPF, broad spectrum protection, with globally approved filters that are photostable and mild on skin. Meeting these demands and the current cosmetic regulatory requirements can be difficult and time consuming for a formulator. Zinc oxide (ZnO) is a commonly used inorganic UV filter which offers broad spectrum protection across UVA and UVB regions. Nano forms of ZnO are widely used in sun and skin care products; these offer the added benefit of transparency when applied to the skin. The use of ZnO in UV protection products has increased dramatically in recent years. Year to date, August 2013, there was a 96% increase in the number of sun care products with UV protection claims launched also containing ZnO compared to 5 years ago (Source: Mintel). The Scientific Committee on Consumer Safety (SCCS) considers that the use of nano forms and non-nano forms of ZnO, at concentrations of up to 25% as a UV filter in sunscreens are safe. This opinion regarding ZnO was adopted on 18 September 2012 (SCCS/1489/12). This increased confidence in ZnO is great news for a formulator as a new door has opened to formulating broad spectrum sun care products.

UV filters

There are two types of sunscreen or UV filters available on the market these are organic and inorganic. Organic (or ‘chemical’) sunscreens, such as butyl methoxydibenzoylmethane and benzophenone-3, absorb UV radiation. Inorganic (or ‘physical’) sunscreens are composed of mineral UV filters, such as titanium dioxide (TiO2) and ZnO. By contrast these filters attenuate UV via three mechanisms: absorption, reflection and scattering, as shown in Figure 1. Inorganic sunscreens have long been regarded as safe and effective.1 They are especially preferred by individuals with a high propensity for skin irritation over sunscreen containing organic UV filters which may lead to irritation. As a result of the different mechanisms in Figure 1, inorganic sunscreens attenuate UV over a broader wavelength and this is one of the many key advantages of these materials. Other benefits include increased photostability, wider global approval and the fact they are perceived as more natural and mild. Despite these benefits, the use of older generations of sunscreens based on inorganic UV filters was limited due to poor cosmetic elegance. The large particle sizes of TiO2 and ZnO left a white film on the skin. In the last decade a new generation of sun care formulations have been developed which offer ‘invisible UV protection’ and ‘light and silky’ skin feel. UV filters have evolved along with these trends and now there are many UV filters with novel coatings and dispersions available to offer enhanced aesthetics in the end formulation. These newer dispersions also offer ease of use and improved SPF stability. As a general rule ZnO tends to have high attenuation in the UVA region of the UV spectrum and lower attenuation in the UVB whereas TiO2 tends to have high attenuation in the UVB and lower in the UVA. There are a few exceptions to this rule such as the Solaveil SpeXtra range of TiO2 dispersions which offer broad spectrum protection from a single UV filter. Figure 2 shows the UV-visible properties of a ZnO product (Solaveil CZ-300) compared to a TiO2 product (Solaveil CT-300) both of which are dispersed in caprylic/capric triglyceride. These grades have been optimised for low whitening on the skin as shown by the low attenuation in the visible part of the spectrum.