The laser hair removal clinic I've been going to is trying to get me to come back every 4 weeks for treatments on the bikini and leg areas. The laser they are using is an NdYag. After my first treatment, hair fell out within 2-3 weeks. I had my second treatment 4 weeks later. This time, no hair fell out following treatment. From my understanding, the anagen phase of hair growth on the lower half of the body does not re-occur until a minimum of 6-8 weeks. Please clarify. Is there any scientific basis for why this particular clinic is advocating a 4 week time period between treatments?

That's a good point...How are you paying for your treatments? Is it a package or Pay as You Go? Sometimes we will have patients come in every 4 weeks if the have had 6 treatments and there is less than 50% hair reduction- but typically that only happens with the ones that tan so they have to be treated on the lowest settings therefore minimizing effectiveness.

You are right that the Anagen phase of typical hair cell occurs every 6-8 weeks. The problem is not all hair cells grow in the same phase. Some cells are in catagen phase and telogen phase at any moment. This is the reason why physicians are instructed to treat each area at least 4 - 6 times throughout the year to cover all hair cells in the Anagen phase of hair growth. I train my students to do at least 4 reatments per area. Many doctors treat each area very fast. But they may skip anywhere from 5-10% of any given surface. 4 treatments per area at 1 month interval not only ensure that doctors cover all hair cells during anagen phase and also minimize the chance that any surface was skipped during subsequent treatments.

Check out this link if you would like to learn more about hair follicle, hair growth and other pertinent information.
http://en.wikipedia.org/wiki/Hair_follicle#Hair_growth_cycle_times