The whole idea that prone masturbation is harmful started in 1998 when Dr. Lawrence I. Sank proposed a theory of sexual dysfunction called Traumatic Masturbatory Syndrome (TMS) (1) .
In his journal article, Dr. Sank speculated that the habit of masturbating prone (while lying face down — tending to rub penis against your hand, the surface of the floor, bed, pillow, or whatever it is laying on, in order to ejaculate) was responsible for severe sexual problems, including anorgasmia (delayed orgasms) and erectile dysfunction, suffered by four men he examined. (1)
According to Sank, once the four men abandoned prone masturbation and learned to masturbate in a supine position using their hands their masturbating prone habit, their anorgasmia and erectile dysfunction supposedly became a thing of the past (they were cured of their sexual dysfunction) (1) .
Sank's theory isn't widely recognized in the medical community and it is not generally accepted, because:
- It experiences on only 4 guys.
- Sexual dysfunction can be caused by stressors in a person's emotional, psychological and/or physical well-being anyway.
- There has been no follow-up research to see if his claims are valid (e.g prone masturbation causes male sexual dysfunction).
Some sources, however, give credence to the idea; but they do not prove anything:
- One sex therapist has condemned masturbation by rubbing against a pillow or mattress (2) .
- Some people suggested that masturbation could play in male psychogenic sexual dysfunction (MPSD), citing Sank as their authority (3) .
- Paul Joanides, a sex guide, quoted an unidentified urologist as saying:
It seems possible that some men who always masturbate face down have
erection problems when trying to have sex with a woman. (4)
And so on.
The answer to your question is: Inconclusive. More research needs to be done, in order to provide a scientific answer on this website.
(1) Lawrence I. Sank. "Traumatic Masturbatory Syndrome." Journal of Sex and Marital Therapy 24(1): 37-42 (1998).
(2) Eva Margolies. Undressing the American Male: Men with Sexual Problems and What Women Can Do to Help Them. New York: Penguin, 1994.
(3) Josie Lipsith, Damian McCann, and David Goldmeier. Male Psychogenic Sexual Dysfunction: The Role of Masturbation. Sexual and Relationship Therapy 18: 448-471 (2003).
(4) Joanides, Paul (2004) Guide to Getting It On, p. 396