The short answer is very likely no. In fact, of over 10,000 Mylash customers, none have ever reported this side effect. It is often reported that bimatoprost, the active ingredient of Mylash Growth Treatment and Latisse, can change your iris colour (typically making it darker). It is very rare for people to have this side effect when using this drug for eyelash enhancement and is normally because it has been put in the eye itself rather than along the base of the eyelashes. This is one of the reasons we've carefully sourced specially designed hydrophobic (water-repelling) micro-applicators that make it easy to put the perfect amount onto the exact part of the eyelid required to stimulate your lash growth. In America where this treatment is more common the incidence of iris colour change from Latisse is close to zero. Information is available on this website about how to do this properly.