Is masturbating bad for overall health?
The act in and of itself is most definitely not bad for your overall health in many cases. In fact, it may be healthy! Most obviously, it seems to be a form of aerobic exercise, where you are working your heart over a small or long period of time. I will say, though, that no credible research has been done on this specific subject. However, any time you are engaged in exercise, it is healthy for your body, as long as your body can handle it!
Secondly, for males, some studies (see link below for Prostate Cancer) have shown that a higher ejaculation frequency correlates with a decreased risk for prostate cancer. I say "some" because the most credible studies that isolated for ejaculation frequency and ONLY ejaculation frequency suggested this possible correlation. Other studies have suggested the opposite link, that ejaculation frequency can demonstrate an increased risk of prostate cancer; however, they used "sexual activity" as the marker for ejaculation and did not necessarily include masturbation or exclude sex without ejaculation.
Again, I said before in "many cases" it is not bad for your health. However, if you masturbate in an unhealthy way, then it can certainly be bad for you! The link I cited below (for Masturbation) gives examples of problems involving insertion of objects into orifices which can be dangerous if done improperly. Full-on traumatizing of tissues is almost universally bad, too. Finally, if your cardiovascular system is not up for the increase in heart rate or other physiological effects of masturbation, it can be dangerous for the same reason other strenuous physical activity can be bad for you.
I hope that helps!
Disclaimer: As a teacher, I most certainly never gave any sorts of lessons or talks about ANYTHING sexual with students unless it was part of a classroom lesson and unless I had the permission of parents to do so. Similarly, I do not condone or condemn masturbation as an act, nor do I codone or condemn any other sort of sexual behavior that is not criminal in nature.