I am working with a 15 year old male who has issues of taking his mother and sisters underwear to masturbate in. He has not acted out sexually in any other way. His mother is insistent that she wants to let him buy his own female underwear. I have been working with this young man to replace this fetish with appropriate masturbation and fantasies. Any suggestions?
Conditioning techniques for changing sexual interests were widely attempted in the 1960s and 70s, but there has not been any good evidence for their efficacy. Fetishes appear to be a lifelong phenomenon, and the best intervention (in my opinion) is to help such people integrate their fetishes into their lives in a prosocial manner.
Clinically, I have seen variants of panty fetishes. For some folk, it is the lacey and silky textures that are the focus of the interest. For these people, purchasing garments of the sexual interest can indeed be appropriate.
Other folk are aroused specifically by used panties. They typically report that it's the scent and signs of its use that are arousing. For people with this type of interest, panties purchased new would not be of any more interest than they would be to any other male.
I have also encountered panty fetishists for whom the act of stealing is part of the interest. For a person of this type, even having other people “donate” used underwear would not be sufficient.
So, it is often helpful to explore thoroughly the nature of the fetish. What exactly are the aspects of the object that excite the person? When the person doesn't have the object available, what are in the masturbatory fantasies? Does the person ever put the panties on? Are other female garments ever of sexual interest? Once the clinician appreciated the basis of the sexual interest, the clinician can begin to help the patient/client formulate ways to actualize it.