Can the results of laser hair removal of dark brown body hair be considered permanent?
The simple answer is no (although you will see ads to the contrary), but there are better answers. The FDA has allowed several laser manufacturers to claim permanent hair "reduction" rather than removal.
You can accomplish this in a series of treatments. A single laser treatment affects the portion of the hair follicles that are in active growth phase, but there are always dormant follicles. Subsequent laser treatments work on those previously dormant follicles as they become active.
Typical patients see dramatic reduction in darker, thicker hair, becoming more sparse, finer and lighter, and much less visible. The best candidates have darker hair, as you mentioned, and lighter skin tones. However there are laser wavelengths that safely treat darker skin types (even Asian or African-American). Popular areas are the under-arm, bikini areas, face and the legs.
Our website www.ExpertPlasticSurgeon.com has additional information.
Laser hair removal has been available for 16 years and has been perfected in the last 8 - 10 years. Many patients in my medical spa have had unwanted hair removed that has not grown back. It may be too early to call this permanent, but patients are very happy with the results.
If "permanent" to you means zero chance of hair regrowth ever, then the answer is "no" - laser hair removal has not been proven scientifically to be quite this effective.
Think of it instead as very good long-term hair reduction.
All the best,