Celibacy and contradiction with modern medical science Buddhism stress on Celibacy at the same time insists on revoking everything that could not be proved by scientific method or rational thought. I am a graduate student of physics and I found that modern medical science or the proponents of medicine recommends controlled masturbation as a healthy way to relieve sexual desire or tension. I find it contradictory that what the medical practitioners found by scientific methods is completely against the view of masturbation in Buddhism and still Buddhism as far as I know advocates the scientific method be more fruitful than the intuitive way of reasoning. Is it contradictory?
I  will quote/extract a few sentences from Wikipedia's article on that subject, below (you can read the whole article and its references for further details):

An article from Beliefnet and Brian Schell, a writer for DailyBuddhism.com, both suggest that masturbation is essentially harmless for a layperson, at least outside the realm of karma[3][4] The accomplished Theravadin monk Bhante Shravasti Dhammika cites the Vinaya Pitaka in his online Guide to Buddhism A to Z, stating the following

Some people during the Buddha’s time believed that masturbation could have a therapeutic effect on the mind and the body (Vin. III, 109), although the Buddha disagreed with this. According to the Vinaya, it is an offence of some seriousness for monks or nuns to masturbate (Vin. III, 111) although the Buddha gave no guidance on this matter to lay people. However, Buddhism could agree with contemporary medical opinion that masturbation is a normal expression of the sexual drive and is physically and psychologically harmless, as long as it does not become a preoccupation or a substitute for ordinary sexual relations. Guilt and self-disgust about masturbating is certainly more harmful than masturbation itself.

The emphasis on chastity in Buddhism is much more so for bhikkus and bhikkunis (monks and nuns, respectively), who are expected to follow the Vinaya (traditional code of ethics for Buddhist monks and nuns). Not only are monastics celibate, but they also must strive to conquer their desires much more so than a layperson.
Thus, in Buddhism, masturbation and its permissiveness is most often viewed as situational, depending on one's level of precepts and monastic standing.

The &quot;Buddhist stress on celibacy&quot; which you refer to is (arguably) 'stressed' for monks and nuns; and it is not stressed in exactly the same way for laypeople.
Some of the other Vinaya rules too (e.g. not eating after noon), which are only applicable to monks and nuns, might or might not not be perfectly in line with every recommendation of &quot;modern medical science&quot;, but apparently they are good enough for their purpose, which I think is to 'allow the holy life to be lived'.
Also, science and Buddhism don't contradict each other on this subject, they say different things about it:

Science suggests that masturbation might have some effect on the incidence of some types of physical illness.

Perhaps Buddhism doesn't say much on that subject (see &quot;Buddha gave no guidance on this matter to lay people&quot; above), but if anything IMO it suggests that masturbation might have some other effects (e.g. on discipline, views about desire, profitable use of time, etc.).