The history of medicine is replete with theories that reflect religious beliefs rather than scientific facts. One of the most interesting, and most instructive examples of this phenomenon is the claim that masturbation causes insanity.
Masturbatory insanity pre-occupied medical professionals for almost 250 years. It arose apparently de novo in Europe in the early eighteenth century, and was not finally put to rest until the middle of the twentieth century. Its history of the idea is recounted exhaustively in the scientific paper Masturbatory Insanity: The History of an Idea by E.H. Hare published in the Journal of Mental Science in January, 1962.
Classical medical professionals made no reference to any harmful effects of masturbation. It was not until the early eighteenth century that the idea gained currency upon publication of the book Onania, or the Heinous Sin of Self-Pollution. The author is believed to have been a "clergyman turned quack" and not a reputable medical professional. Like most quacks he advertised an extremely expensive secret remedy.
The assertions gained wide popularity, though. Voltaire, writing in his Dictionnaire Philosophiqe in 1764 reports that the book was then in its 80th edition.
During the following years anatomical and pathological study revealed that disease was caused by structural abnormality or derangement, and the claim that masturbation could cause "deterioration of the eyesight, disorders of digestion, etc." lost currency. But medical professionals refused to give up the idea that masturbation was harmful and the locus of harm became mental health.
The third natural family I would assign to the masturbators… I think it cannot be denied that that vice produces a group of symptoms which are quite characteristic and easily recognized, and give to the cases a special natural history: the peculiar imbecility and shy habits of the very youthful victim; the suspicion and fear and dread and suicidal impulses and scared look and feeble body of the older offenders, passing gradually into Dementia or Fatuity.
Nor is it difficult, from our present standpoint, to see how this came about. Masturbation is most commonly and most frequently practised during adolescence and therefore most likely to be observed when mental disease insidiously deprives an adolescent of his normal social inhibitions.
As the field of psychiatry developed, it was recognized that excessive or public masturbation was a symptom of serious psychiatric illness, not its cause. Even then, the psychiatric profession only gradually gave up the notion of masturbation as harmful, downgrading it from psychosis to neurosis and ultimately acknowledging it as normal behavior.
The story of masturbatory insanity is a cautionary tale. It reflects the injection of religion into medicine, characterizing a behavior as harmful because religion says it is harmful, rather than relying on scientific evidence. We may imagine that, in our purported sophistication, we would never fall prey to such ludicrous theories. But, in fact, similar efforts are ongoing, with religious conservatives trying to persuade the public that homosexuality is deviant behavior and that abortion is physically harmful.
The story of masturbatory insanity should remind us to be aware of the intersection of religion and culture with contemporary medicine. Great harm can occur when religion is confused with medicine and medicine is harnessed for religious ends.