While I’m on rounds with students I like to ask, “What is the active ingredient of hydrogel?” My query is usually met with puzzled looks. It’s a trick question, because the term “active ingredient” generally applies to pharmacologic agents that undergo metabolic change in biologic systems. The active ingredient of hydrogel which gives this substance its name is water. Compounds are added to thicken the mixture and provide viscosity, such as glycerine. Other ingredients common in cosmetics, such as aloe vera, methyl paraben, hydrogenated castor oil, and propyl paraben, are added to hydrogel depending on the manufacturer …
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