Laser will only stop working if your hair gets too light (blonde or gray) to absorb the light energy. IIRC even really fine hairs still "burn" when lased. Facial hair seems to be very stubborn with some people. My beard and neck has also been very resistant to IPL treatment, even though it's pretty dark and thick. I think I've hit it about a dozen times and it's slowed down but not stopped growth. Hopefully, it will eventually give up and die(die! die! die! LOL!).