Semi permanent eyelash extension treatment for women who want to lengthen their lashes and define their eyesit has been carefully developed by experts to produce longer thicker and very natural looking lashes that last up to six weeks and longer if you take care of them and have them in filled how long do semi permanent eyelash extensions last the truth is that a natural eyelash has only a 2 3 month lifecycle in order to apply a synthetic eyelash to a natural hair the natural hair