We’ve all heard the warning: If you stay in the hot tub too long, you’ll become impotent. The truth is, there isn’t much scientific basis for this one. If you’re obese, smoke, or dabble in steroids, though? Well, let’s just say it hurts your chances of getting pregnant as much as you getting a date. We pored over prominent studies and reached out to Dr. James F. Smith, director of male reproductive health at the University of California, San Francisco to help guide us through the truths (and half-truths) about what’s killing your sperm. 

Show Stoppers

Smoking tobacco: Tobacco has been linked to sperm that is abnormal in terms of movement (motility), appearance, and ability to fertilize. The chemicals in cigarettes may also damage DNA. Women exposed to secondhand smoke while pregnant are 20 percent more likely to give birth to a low-birth-weight baby, according to the Centers for Disease Control and Prevention.

Being obese: Without question, this is a fertility blocker: Obesity can reduce circulation, which plays an important role in erection, and directly impair sperm through hormonal changes.

Having sex too often: Most men need approximately 48 hours after an ejaculation to produce the optimal amount of sperm. The more a man ejaculates in close succession, the lower his count will likely be.

Not having sex often enough: If a man waits more than about three days after a prior ejaculation to ejaculate again, some of the sperm in his ejaculate may decrease in quality. According to a 2009 study, daily sex may make for healthier sperm because it reduces exposure of these cells to free radicals.

Having radiation or chemotherapy: These potentially live-saving treatments can have severe side effects, including infertility. “Chemotherapy and radiation therapy are always a very significant risk factor,” says Smith. Some men even choose to store sperm in advance of these treatments in order to have it available for future pregnancies in case these interventions result in fertility problems.

Using steroids or testosterone: A well-known side effect of anabolic steroid use is testicles shrinkage. Alongside that, these drugs can reduce sperm production. Contrary to what a person might assume, Smith says that testosterone almost always hurts sperm production. “While most of the time this damage is reversible, for some men, this damage can be permanent,” he says.

Having diabetes: Regardless of weight, having Type 1 or Type 2 diabetes can lead to sperm problems. This can occur through issues with retrograde ejaculation, where sperm travels up to the bladder during orgasm rather than out of the tip of the penis. Men who experience poor blood sugar control for long periods of time may develop this due to nerve damage in the bladder.

Proceed with Caution

Smoking pot: Research is still sparse linking pot use and lower sperm quality and quantity, but recent findings suggest that smoking more than once a week was associated with a sperm count reduction of 30 percent. Smith says it’s possible that marijuana impacts sperm through hormonal changes.

Using a computer: Another case of excessive heat exposure, laptops may overwarm the scrotum if they are on the lap for extended periods of time. If you have a hot computer on your lap, take it off.

Drinking: There is a little evidence that moderate drinking may protect sperm via antioxidant activity. But there’s certain proof that heavy drinking can lead to lower testosterone levels, lower sperm count, and sperm that is less mobile and more likely to be shaped unusually.

Using Propecia: Studies have shown that even low doses of finasteride, the active ingredient in the hair loss treatment Propecia, may lower sperm count. In a 2013 analysis of 4,400 men who used this treatment, there was an 11.6-fold increase in sperm count once they discontinued use.

The Jury Is Still Out

Cooking a lot: Back in 2007, celebrity chef Gordon Ramsay told Larry Kingthat his problems with low sperm count may have been due to long hours spent in front of a hot stove. As with hot-tubbing, there isn’t firm evidence that this negatively impacts sperm, but Smith says, for men who are dealing with infertility, it may be a behavior worth modifying.

Cycling: Smith says that the effects of cycling on sperm quality are probably only of consequence to men who are elite athletes, such as those involved in Iron Man triathlons or who participate often in century rides. In general, he says that cycling would likely do more good than harm for most men because of the benefits of regular exercise on fertility and overall health.

Wearing the Wrong Underwear: A 2012 study that had five fertile men wear underwear specially designed to keep the genitals close to the body for 120 days led to increased DNA issues in the sperm, lower count, and less moving and viable sperm. The catch? This was bizarrely tight underwear and sperm measurements all returned to normal a couple months after the men switched back to their usual undergarments.

Getting kicked in the balls: Unless there was very serious trauma — as in emergency-room serious — a hit to the goods is not likely to hurt your sperm. Signs of worrisome injury to the testicles include swelling or bruising, extended nausea or vomiting, and a twisted or ruptured testicle.

Watching too much TV: According to a Harvard study men who watched 20 hours of TV per week had sperm counts around half of those of men who watched nearly no TV. But is the television itself really to blame?

Hot-tubbing: Scientific evidence for this is limited, but soaking in hot tubs (or even hot baths) may temporarily hurt your sperm count — if in excess. Still, Smith says he does discourage this activity in men who are dealing with infertility.

Source: Mens Journal