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Micro-sponges utilize micro-entrapment technology wherein the shell surrounding the active ingredient has a porous structure rather than a continuous shell structure as in a microcapsule [49]. The porous shell results in sustained release of the active ingredient(s) over longer periods of time. The spheres can be programmed to release active ingredient(s) with the use of different triggers such as applied pressure or the introduction of water [49]. Entrapment systems can control the release of actives onto the epidermis, thus reducing irritation while maintaining efficacy. An example of increased efficacy and reduced irritation with use of micro-sponges is that observed with benzoyl peroxide entrapped in a micro-sponge system [50]. Micro-sponges reduce unpleasant characteristics of the main ingredient, as has been observed with zinc pyrithione and selenium sulfide [51].