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Comparatively Speaking: SPF vs. FEF
By: Anthony J. O'Lenick Jr., Siltech LLC; and Thomas O'Lenick, PhD, SurfaTech Corp.
Posted: August 30, 2011
page 3 of 3
Formulation chemists have the task of improving all aspects of sunscreens including improving SPF. The two most common ways of increasing a formulation’s SPF are: increasing the amount of actives in formulation and utilizing synergistic effects to boost the ability of an active to absorb or reflect the sun’s radiation. As show in Table 2, increasing the actives concentration in the formulation will increase the SPF.
In this case, the SPF increased from 30 to 50 but the FEF only increased from 115.4 to 156.3. The major drawback in this method is the concentration increase of actives. The sunscreen actives are small organic molecules or inorganic nanoparticles such as zinc oxide or titanium dioxide.
The increase in concentration becomes a major problem for the formulation chemist for a couple of reasons. First, increasing the amount of small organic molecules that penetrate the skin is a major concern, and the FDA limits the amount of organic actives used in formulations due to health concerns. Therefore, formulators often use a synergistic effect in formulation to maximize the ability of the actives to absorb or reflect the UV radiation. In "The Effects of Solvents on Sunscreens: A New Ester to Improve Efficiency," an article in the June 2011 issue of Cosmetic & Toiletries magazine by T O'Lenick, PhD, and D Lott, solvent effects on several common sunscreen formulations were compared. This article shows that adding sorbeth 2 hexaoleate into a given formulation can boost the SPF of an oil based sunscreen from 18.1 (no sorbeth 2 hexaoleate) to 58.9 (39.0% sorbeth 2 hexaoleate). The addition of this ester can also increase the FEF of the formulation.
As shown in Table 3, adding sorbeth 2 hexaoleate into a formulation can increase both SPF and FEF without increasing the concentration of actives. The addition of this ester makes the actives more efficient; therefore, the concentration of actives can be decreased while maintaining the same SPF value. Not only is SPF improved but FEF is increased. Increasing the efficiency of a formulation will allow for sunscreens to decrease the amount of expensive actives and maintain the same SPF value.