A lash lift is a semi-permanent procedure that gives you the appearance of fuller, thicker eyelashes without the use of any leave-on chemicals or extensions. The natural lashes are boosted from the root, giving them a lifted, lengthened appearance. The results typically last four to six weeks, depending on how quickly your eyelashes grow. You should avoid mascara for 48 hours after the treatment and leave lashes untouched for at least a full day.