A seminal sperm study released in July conclusively showed that sperm counts among Western men had declined almost 60 percent over the last four decades.

Even more alarming than the drastic drop in those vital bodily fluids? The fact that the scientists who ran the study weren’t able to identify a solid reason why sperm counts had so drastically dwindled.

Though the answers remain unknown, Allan Pacey, an expert in sperm science at the University of Sheffield, talked with Inverse about four factors that could be cramping sperm’s style.

4. Issues in Utero

“The first and most important [sperm-shaping event] happened before he was even born,” Pacey says. While in their mother’s uterus, fetuses are being bombarded by hormones, chemicals, and genetic switches that shape their future development. Though the testicles won’t descend for many more years, gonads are formed in utero — and their future is written in genetic code. “And there’s fairly reasonable evidence that can go wrong,” he adds.

Basically, the size of the factory (in this case, the testicles) determines the number of goods (sperm) that can be produced. Though it’s nearly impossible to study this phenomenon because it involves so many complex mother-child interactions, a handful of studies show that certain chemicals in the womb can shrink the factory’s long-term potential.

Men born to women who smoked during pregnancy, for example, had lower sperm counts than those born to moms who didn’t smoke. Additionally, sperm counts also declined in men whose mothers ate seven or more meals with red meat each week during pregnancy. Crucially, it wasn’t the meat itself, but the growth hormones pumped into the beef, whose artificial chemicals negatively impacted the gonads of the developing fetus.

3. Skinny Pants Syndrome

What happens in the womb sets the stage for a lifetime of sperm production, but Pacey says people make decisions that negatively affect their sperm count everyday.

“The single biggest risk factor for how many swimming sperm he produced each day was whether he was wearing tight pants or loose pants.” The tighter the clothes, the more liable the testicles are move up toward his body’s warm core. And because the scrotum has to be relatively cool to produce healthy sperm, any kind of intense heat, whether it’s from your laptop or by your itsy bitsy mankini, can send sperm counts dwindling.

Fortunately, what you choose to wear will only affect you for three months, even though what happened in the womb will stay with you forever. That’s because three months is about how long it takes to make a fresh batch of sperm from start to finish.

See also: Scientists Have Figured Out Why Sperm Bends

2. Bad Diets

A 1996 study showed that low antioxidants can damage sperm DNA. A 2005 study later showed that taking oral antioxidants reduced DNA fragmentation in sperm. This jives well with other research that shows that obesity can serve a big blow to a man’s fertility.

1. Spermicidal Substances

Mom’s tobacco use isn’t the only thing that can disrupt sperm production. A dude’s own cigarette habit can reduce his fertility, too. In 2005, a study in BJU International showed that smoking reduced the volume of semen a man produced, though its fundamental structure appeared intact. And that’s not the only substance to reconsider. A 2014 study in the journal BMJ suggests that the more frequently a man drinks alcohol, the more likely his sperm was going to be total crap.

See also: Sperm Radar Might Illuminate Male Infertility

So What Can We Do About It?

Though the decline in sperm count in European and American men over the past 40 years is alarming, Pacey says it’s not time to panic yet. Men who are struggling to conceive with their partner can see a doctor and talk through the individual challenges they may be facing. And people who aren’t trying to conceive are probably oblivious to their sperm count anyway and can just go about living their normal lives.

“The change that’s been seen was from normal to normal,” Pacey says. “It’s not yet gone to the point of being critical. The interesting question is, ‘Are we getting close?’ And I don’t know.”

Photos via Eleanor Cummins