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UV Filter
Comparatively Speaking: UVA vs. UVB Protection
By: Anthony J. O'Lenick Jr., Siltech LLC
Posted: July 27, 2010
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It is important for the formulator to be cognizant of the physical nature of the sunscreens. For example, avobenzone and oxybenzone are crystalline and must be dissolved in a suitable solvent. They, like the other oil-soluble UV filters, should be formulated in the oil phase of an emulsion. Even if the sunscreen is a liquid, the miscibility in the formulation is crucial. On the other hand, ensulizole is a water-soluble sunscreen and should be added to the water phase of an emulsion. Obviously, if formulating a water resistant-sunscreen, water solubility or insolubility of a sunscreen is of prime importance.
The mix of UV filters is important for an absorbance balance, and this mix can also be extremely important from a photostability standpoint, as some UV filters actually catalyze the photodegradation of other UV filters.