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Dispelling the 'Law of Wiechers' and Maximizing Actives Delivery
By: Johann W. Wiechers, PhD, JW Solutions
Posted: December 16, 2010
page 2 of 4
Hadgraft explained, “Every active in cosmetics needs to be included at a level of 3%. That is the 'Law of Wiechers in Cosmetics.' It doesn’t make any difference what the active does or doesn’t do, the level is always 3%.”
I quickly realized that he was right. Almost every supplier tells the formulator that his active ingredient must be included at 3%. If the molecule is too active, it is diluted in such a way that 3% of a dilution must be added.
Hadgraft continued, “Wiechers [also] has told you to formulate an active ingredient at a level close to the maximum solubility limit in that vehicle to get close to maximum delivery, which is correct. [But] why, then, is it that the 'Law of Wiechers' dictates that every cosmetic active needs to be formulated at 3%? It is wrong!"
There Hadgraft and I agreed again, but I wondered why would he name this unwritten law in cosmetics after me. Upon further discussion, Hadgraft argued that in pharmaceutics and cosmetics, when scientists have no idea how to deliver a drug into the skin, they add it at a level that has been shown, in in vitro skin penetration experiments, to deliver the drug in reasonable quantities. Then they make a series of formulations containing smaller (and sometimes higher) concentrations to create pharmaceutical formulations with more or less efficacy.
Topical corticosteroids are a typical example of this approach but in cosmetics, he argued, it is even worse. In cosmetics, 3% should always be the amount of active although cosmetic manufacturers always formulate with less. Consumers then complain that cosmetics are not effective and according to suppliers, this is because the active amount is too small. To this point, Hadgraft argued, “Only we know that a formulator can make a 10% formulation that does not deliver at all and a 0.1% formulation that delivers perfectly. Why are we, plus a handful of skin delivery scientists, the only people to understand this?”