Yes, the reason many professional beauty supply stores only sell to licensed personnell only is to keep certian lines "restricted", but the main reason is the chemicals contained within certian products.
Hair colouring, perms, and other products that chemically alter human hair, can cause GREAT and sometimes permanent physical damage if not used properly. Many products do not come with step by step directions for use either, assuming the professional will know the proper procedures.
Having worked in a hair salon and taken series of courses while at school, am in no way an expert, but can spot a home/bad dye/perm job a mile away. Have also seen some horrible cases of persons with everything from bright orange/green hair, to gaping bald spots (some that never regrew hair), to very nasty allergic reactions. All from people who got their hands on professional products and thought there was "nothing to it".
Now, as for shampoo's,conditioners,and other "care" products, have found mixed results. Some professional products are wonderful, others no better than what one can get at K-Mart.
Those commercials telling persons not to purchase say, "Paul Mitchell" products anywhere else but a salon crack me up. One can get Paul Mitchell, Sebastian and countless other "professional only" hair care products at most discount drug chains or local pharmacy/shop. It has been that way for years and if it was being done illegally considering the vast amount of suing that goes on in the USA, it would have been stopped by now.
With the advent of eBay, one can find almost anything "professional", even some of the most hard to get one's hands on products. My hairdresser was NOT happy when I told him I bought a job lot of the same product he charges $$$ on eBay for only $.
L.
