Steriod Use Legit: Any kind of testosterone supplementation including anabolic steroids -- the kind used by athletes and the insanely vain -- can decrease testicular function and thus dramatically reduce fertility. (For more details, see Dr. Ken's article on the effects of steroids.)
Kevin Winter, ACMA / Getty Images
Drinking Mountain Dew Bogus: Doing the Dew won't affect your sperm count in any way. There have been rumors about other soft drinks, as well, and these are also incorrect. (Decreasing soda intake is worth considering given the empty calories and potentially harmful chemicals the drinks often contain.)
Joe Raedle, Getty Images
Plastics Legit: Certain chemicals found in consumer products are associated with impaired sperm production. 1. Phthalates are nearly ubiquitous in household products, such as food packaging, shower curtains, coatings on medicines, shampoos and many others. 2. Bis-phenol A is already banned in some countries (but not in the U.S.). It's a chemical found in polycarbonate plastics, the type used in the hard plastic water containers. These can be hard to avoid but some manufacturers are beginning to label their chemical-free products. To the extent you can, avoid eating, storing and microwaving foods and beverages in plastics.
Lluis Gene, AFP / Getty Images
Bicycle Seats Legit: Sitting on non-ergonomically shaped bicycle seats for prolonged periods can do two things. 1. They can raise your scrotal temperature, which can decrease sperm production. 2. They can damage the blood vessels that carry blood (i.e., nutrients) to the testicles. Softer seats and taking breaks can help you avoid this.
Paul White, AP
Keeping a cell phone in your front pocket Legit: It has been repeatedly demonstrated that cell phone exposure can harm sperm function. In general, the farther you keep the cell phone away from your boys, the better. (For more details, see Dr. Ken's article on the effects of cell-phone use.)
Yoshikazu Tsuno, AFP / Getty Images
Caffeine Bogus: Shooting blanks is not likely to occur as a result of coffee, tea or even No-Doz. Excessive intake may have a very slight effect, but your cup of morning of coffee won't have any meaningful impact.
Earl S. Cryer, AFP / Getty Images
Smoking Legit: Men who smoke cigarettes are more likely to have lowered sperm counts. Yet another reason to stop paying the big tobacco corporations to poison you.
Excessive masturbation Bogus: Masturbation will not cause infertility or, for that matter, blindness or hairy palms. If it did, the human race would have died out long ago.
Bonnie Biess, Asylum.com
Smoking marijuana Legit: Chronic and frequent marijuana use impairs sperm and lowers sperm count. It also lowers testosterone levels, which can lead to impotence, loss of interest in sex and gynecomastia, aka "man boobs." (For more details, see Dr. Ken's article on the causes of man boobs.)
Regularly placing a laptop on your lap Legit: If you keep a laptop in your lap, the heat emitted can increase the temperature of the testicles and may consequently decrease sperm production. Keep the laptop on the desk or use a laptop board or pillow to create a buffer in between the computer and you.