They grow back: If you just pull out an eyelash, it will grow back in about 3 to 4 weeks. If you break an eyelash while trying to pull it out, the broken eyelash will continue to grow. The only time an eyelash will not grow back is when the hair bulb is damaged, either by disease or injury. ...Read more. months: Eyelashes grow out in the 3 month cycle. If you cut one it will not grow by itself but new replcement ones grow alll the time. It will take a maximum of three months to get a whole new set. ...Read more.