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Sunscreens for Today’s Clients

By: Rachel Ametsitsi, Ada S. Polla and Anne Pouillot
Posted: January 2, 2014, from the January 2014 issue of Skin Inc. magazine.

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Physical blocks. Physical blocks are substances with a particle size of about 200–400 µm that act by reflecting solar radiation. The most commonly used blocks are titanium oxide, zinc oxide, iron oxide, mica and silica. The last three mentioned are not sunscreens, but soft-focus effect powders. When incorporated into a cream at such size, titanium and zinc oxides often leave an unsightly white deposit on the skin, which consumers dislike. These compounds, however, are very well tolerated by most skin types, because they do not penetrate the skin, resulting in minimal adverse effects.

Iron oxide, mica and silica are not sunscreen ingredients. From a regulatory perspective, they are considered cosmetic ingredients or excipients that provide skin-coloration or assist in formulation elegance. However, given their particle size, these compounds act as particulate matters that may reflect and scatter UV radiation, although they are not regularly accepted as active sunscreen ingredients.5 Table 2 lists the properties of titanium dioxide and zinc oxide.

Physical filters. The most common example of a physical (mineral) filter is titanium oxide in particle sizes ranging between 15–80 nm. These particles absorb both UVB and UVA radiation. Due to their small size, they do not leave a white deposit on skin upon application, an advantage that is appealing to consumers. However, some have reported that this ingredient leaves a sensation of dryness on the skin.

Chemical filters. Chemical filters are compounds that have one or more aromatic rings fixed on the carbonyl groups associated with a substituent donor of electrons and/or unsaturated carbon chains. Chemical filters are characterized by the wavelength at the absorption maximum, and by their absorption coefficient, which is a unit measure of a chemical filter layer’s ability to absorb the light radiant energy.

Chemical filters have the advantage of being very elegant in cream formulations—the product does not feel heavy, oily or leave a white film. However, chemical filters are known to cause allergic contact dermatitis, irritative dermatitis and photosensitivity.6 The filters that most commonly cause such skin reactions include: benzophenones (benzophenone-3 or oxybenzone), butyl methoxydibenzoylmethane, methoxycinnamate, methylbenzylidene-camphor and aminobenzoic acid. Table 3 on Pages 61 and 62 lists the advantages and limitations of chemical filters.7, 8, 9

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