hello , all interesting topic Masturbation , is forbidden in Islam aswell , Prophet Mohammed said : said, 'O group of youth! Whoever from among you can marry should do so because it keeps the gaze low and it protects the private parts. And he who cannot marry should make it compulsory upon himself to fast because it breaks lust.' i also heard from a doctor here in the netherlands , that masturbation can cause damage to the body aswell. both Physically and Mentally,
Masturbation is
NOT prohibited in Islam. Nor above hadith proves such.
"Protect private parts" means that it protect them from being used illegally(adultory)
It's only that marrying is very much recommended in Islam. So we can say that Islam
discourage BUT NOT prohibit masturbation.
But u r right that if one goes
too enthusiastic with masturbation then there can be mechanical damage to
"trabeculae" in
"corpus cavernosum" of penis which can have permanent bearing on erection.
Also some ppl use extreme methods like tying rope etc, can cause damage.
Also prolonged continuous erection can cause damage to trabeculae.
So ur doc was very right at least about PHYSICAL damage.