Does Missing a Session of Laser Hair Removal Mean I Have to Start From the Beginning?

Laser hair reduction treatments should be done at intervals of 4 weeks, due to the growth cycle of the hair follicle, the laser only damages the follicle when it is in its "growth" Stage.  You do not have to start treatments over necessarily but I would start spacing them at 4 week intervals for best results. 

I usually recommend an interval of 4-6 weeks.  Depending on the area, as few as 15% of hairs may be in anagen or growing phase.  Using the 4-6 week interval, there is synchronization of the growth phases of the hair follicles and more hair follicles are affected by the laser treatment.

Longer intervals than this decrease this synchronization.

If you were having your laser hair removal treatments every 12 weeks, and now it's been 16 weeks before your next one, this should not make a major difference. Regardless of the frequency of laser treatments, sometimes we see a paradoxical or 'unexpected' effect of hair stimulation (partial or significant) after laser treatment for hair reduction. I would recommend that you continue your sessions and try to schedule them every four to eight weeks maximum. Discuss with your doctor energy settings, so that the highest safe level can be used in you each time, avoiding partial regrowth of hair. No physician can predict who may get this uncommon phenomenon. Good luck! Dr. Bowes