Trying to Get Pregnant? 10 Proven Sperm Killers

By Erica Kain

When it comes to conceiving a child, there are lots of things that can go wrong—sperm allergies, poor egg quality, and ineffective sperm. Of the approximately 1 in 10 couples who are infertile, it has been estimated that male factors alone contribute to 30% of these cases.

Though men produce millions of sperm a day (compared to the 300–400 eggs that women release during their lifetime), external factors (like temperature) can affect the health of these little swimmers. And because sperm cells take about 75 days to grow to maturity, harming them can affect your fertility.

Here are 10 surprising factors that may affect a man’s sperm.

Human testes cannot function properly unless they are able to stay cooler than the rest of the body. Thankfully, the male anatomy is designed to create distance between the testes and the core body temperature.

If the temperature of the testicles is raised to 98˚, sperm production ceases, according to Hal Danzer, MD, a Los Angeles fertility specialist. When production is interrupted, sperm can be negatively impacted for months.

But what happens if heat exposure does wreak havoc on a man’s reproductive capabilities? “The overall number [of sperm] can be lower, as well as the motility and morphology,” says Paul Shin, MD, a urologist in Washington, D.C.

There is a grain of truth in the myth about hot tubs preventing pregnancy. “Wet heat” isn’t good for the testes, and, according to a study published in 2007, even 30 minutes in a Jacuzzi or hot tub can temporarily decrease sperm production.

However, this study also showed that the negative effects of wet heat on sperm may be reversible.

Dr. Shin counters that wet heat exposure can impact a man’s sperm for a surprisingly long time. Because sperm takes so long to mature, “any interventions [to reduce exposure] will usually take at least three, if not six to nine, months to show any benefit,” he says.

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“When I know that a man hasn’t been in a hot tub, smoking dope, or wearing bicycle pants, and that the collection technique for his semen analysis was good, my first question is, ‘Were you sick three months ago?’” says Kurt Wharton, MD, a San Francisco ob-gyn specializing in infertility. Often, he says, these men will acknowledge a recent virus.

A high fever can have the same effect as wet heat on a man’s sperm—with the same lasting effects. And depending on the timing in the sperm production process, sperm concentration can decrease by up to 35% following a fever, according to a 2003 study.

Can a laptop computer really affect a man’s ability to reproduce? According to researchers at the State University of New York at Stony Brook, there is a direct correlation between laptop use and increased scrotum temperature—up to 35˚ in certain positions!

This increase has a well-documented harmful effect on spermatogenesis (the process of male gamete formation), so if you’re trying to conceive, leave the laptop on the desk.

Why do you think Scots brag about their fertility? "It’s their kilts," says Dr. Wharton, though he admits the difference between boxers and briefs is usually not great enough to merit a change in sperm count.

"Boxers are better than briefs, if a man’s sperm count is on the low side. But it probably has little effect if the sperm count is normal," says Dr. Danzer.

However, wearing tight bicycle shorts for an extended period of time is a bad idea as well, Dr. Wharton adds. The more constricted a man’s pants are, the less hospitable an environment he creates for sperm production.

Approximately 15% of men have varicoceles, or enlarged varicose veins in the scrotum, usually in the left testicle. When a man is experiencing a low sperm count, doctors may recommend varicocele repair, a procedure that repairs enlarged varicose veins in the scrotum surgically or via percutaneous embolization, a nonsurgical procedure using a catheter.

Though it’s not clear, a varicocele may interfere with sperm production by interrupting blood flow, overheating the scrotum, or causing blood to back up in the veins supplying the testes. Though there is little proof that fertility improves after varicocele embolization, some doctors believe the surgery may improve semen quality.

The advice about cell phones in proximity to a man’s reproductive organs varies.

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A 2008 study found that men with the highest cell phone usage (more than four hours per day) had significantly lower sperm counts, motility rates, and morphology (normal shapes),” says Dr. Shin. He recommends patients carry their phones in their briefcases rather than pockets in order to limit radiation exposure.

However, because the studies have been small, some doctors disagree. “I don’t advise a man to carry a microwave in his front pocket,” says Dr. Wharton. “But otherwise, it is not a problem.”

“Obesity has been associated with increased production of female hormones (estrogen), decreased sperm counts, sexual dysfunction, and infertility,” says Daniel A. Potter, MD, of the Huntington Reproductive Center in California, who is a fellow of the American College of Obstetricians and Gynecologists.

Compared to normal and overweight men, obese fertile men have reduced testicular function and significantly lower sperm counts, according to a

2009 study by the World Health Organization.

Although obesity reduces sperm count, only extreme levels of obesity may negatively influence male reproductive potential, according to a

2009 study.

“Tobacco, alcohol, and marijuana can impair sexual function,” says Dr. Potter, who recommends that his patients limit or avoid all of these when trying to conceive.

Alcohol abuse negatively affects semen quality and production, while cigarette smoking impairs sperm’s motility, according to

a 2010 study.

In addition to slowing sperm down, other studies show that cigarette smoking can damage sperm DNA and

increase erectile dysfunction.

Marijuana isn’t safe either. Smoking pot has been shown to reduce sperm count, sperm function, and overall male fertility.

According to Dr. Potter, some physiological situations that could negatively affect sperm include:

Blockages. “Whether it’s caused by a birth defect, infection, trauma, or vasectomy, a blockage prevents the sperm from entering the semen,” says Dr. Potter.

Genetic disorders. “Chromosome abnormalities can cause severely diminished or no sperm production,” says Dr. Potter. For example, one form of cystic fibrosis can cause the vas deferens not to form.

Other detrimental factors. Anti-sperm antibodies, hormonal imbalance, testicular cancer, undescended testicles, and sexual problems can affect sperm.