It depends on who applied them , glue being used, maintain and humidity.....… If you follow after instructions, you can redo every 3 weeks even 4 weeks. Keep lash dry for 24-48 hours. As eyelash extensions and glue doesn't like being wet. If you keep lashes Dry for 3-4 weeks,it keeps more percentage than you expected. * Wearing goggle when take a shower or bath, NEVER run into hot steam, it will disable glue . * Using foaming cleanser when sweating or when humidity is high ,purpose of using foaming cleanser, clean All oil from body and cosmetic products on lashes. * Use coating which contains both glue and sealer, make your extensions stay on longer.Coating Instructions may tell you to use once every 3 days, you can try to use every 2 days, it may be even more Helpful. * Wear eyelash extensions mask in case you sleep on either side of your eye, such as a mask similar to bra. Reduces the chance of losing eyelash extensions during sleep. * Stay away from using oil base products over eyelash extensions, as oil always dissolves glue.