Let's start with a True or False question: Masturbation causes emotional problems and harm to one’s body.
What do you think?
The above question is included in a sex and sexuality curriculum I use for young adults and parents. The answer is false [see remarks above], and as the postings in this blog series have iterated, masturbation is now recognized [by whom?] as a healthy and normative ["normative" rather than "normal"] behavior in the human sexual repertoire. But can it become harmful on occasion? Yes, and I have worked with men who have chaffed their penis due to excessive masturbation, had it "caught" or "stuck" in attempts at masturbation without hands via the use of household items (the vacuum cleaner urban legend isn’t necessarily a legend), and damaged relationships when masturbation became the sole outlet in regards to sexual interactions. Still, masturbation by males is generally a healthy behavior [based on today's social indoctrination rather than scientific proof].
Masturbation though does play a pivotal role in the development and maintenance of paraphilias. The American Psychiatric Association defines paraphilia as "recurrent, intense, sexually arousing fantasies, sexual urges, or behaviors ... that cause significant distress or impairment in social, occupational or other areas of functioning."  Some of the more recognized paraphilias include:
- Pedophilia - Sexual activity with a prepubescent child
- Exhibitionism - Exposure of one’s genitals to an unsuspecting stranger
- Frotteurism - Touching and rubbing against a nonconsenting person
- Transvestic fetishism - Sexual arousal to cross-dressing
[Note: The author somehow neglects to consider that today's epidemic use of pornography is itself a form of paraphilia.]
There are also additional paraphilias that are less well known to the general public but still impact the sexual functioning of a significant number of males, including:
- Coprophilia - Sexual excitement by being smeared with and/or ingesting feces
- Necrophilia - Sexual excitement via sexual interaction with a corpse
- Klismaphilia - Sexual excitement by being given an enema
- Asphyxiophilia - Sexual excitement by self-strangulation
And there are many many more.
Understandably, most men with a paraphilia, particularly one that would be socially or legally problematic, attempt to hide their arousal patters and engage in more traditional sexual activity. There are, for example, men who are primarily sexually attracted to children but who have married, raised children, and lived conventional lives while never once betraying the fact of their attraction or acting upon it. Men are also reluctant to inform a new romantic partner of their sexual attraction to feces, urine, insects, corpses, enemas, to wearing a diaper, or to dressing in woman’s clothing and may never do so even after years in a relationship. For most, the closest they come to engaging in the activity is via fantasy and masturbation.
Kafka reported that paraphilias have been ignored in psychology and sex therapy due to the "dearth of prevalence and treatment outcome studies and partly to the hidden nature of these conditions" even though they may "lead to shame, guilt, depression, and often, to negative economic and interpersonal consequences." (p. 442)  Feierman & Feierman described the difficulties in studying paraphilias. First, self-reporting is fraught with dishonesty when it comes to disclosing uncomfortable and embarrassing sexual behaviors. Second, experimental studies in creating paraphilias are unethical. Finally, longitudinal studies of child and adolescent sexual development are not likely to yield much valuable information due to the statistical rarity of paraphilia. 
What we do know is that paraphilic development begins early in life (most males develop a paraphilic interest by the age of 17). The text Human Sexuality summarized the literature regarding the etiology of paraphilia and concluded, "People with paraphilia seem to have grown up in dysfunctional environments and to have had early sexual experiences that limited their ability to be sexually stimulated by consensual sexual activity." (p. 341)  Also, all paraphilias are primarily reinforced by masturbation. Unable to obtain sexual satisfaction by engagement in the activity most sexually stimulating to them, adolescents with paraphilic interest instead use fantasy and masturbation as a primary means of gratification thus keeping their desire hidden and unknown even to the people closest to them. Each episode of masturbation however only further reinforces the paraphilic interest and reduces the possibility of modifying or eradicating it in the future.
When people joke about the harm of masturbation, they almost always neglect to consider its truly most harmful effect. Each time a male masturbates to a paraphilic fantasy he further etches it into the hardwiring of his brain and increases the risk of future "significant distress and impairment," particularly regarding sexual functioning and satisfaction. Once a paraphilic interest has fully developed, it is almost impossible to ameliorate.
 American Psychiatric Association (1994). Diagnostic and statistical manual of mental disorders (4th ed.). Washington, DC: Author.
 Kafka, W.P. (2007). Paraphilia-related disorders. In S.R. Leiblum (Ed.), Principles and practice of sex therapy (pp. 442 - 476). New York: Guilford Press.
 Feierman J.R. & Feierman, L.A. (2000). Paraphilias. In L.T. Szuchman & F. Muscarella (Eds.), Psychological perspectives on human sexuality (pp. 480 - 518). New York: John Wiley & Sons.
 Strong, B., DeVault, C., Sayad, B.W., & Yarber W.L. (2005). Human sexuality: Diversity in contemporary America. Boston: McGraw Hill.