Contrary to what the health teacher  tried to drill into our heads in middle school, it can be  pretty hard to make a baby.

And if fertility isn’t coming  easily, you might find yourself in a bizarre corner of the internet  where people tell you to change your underwear and your chair  and pretty much everything in your life because somehow that’s  all lowering your sperm count. While some of these claims  are just not true, there is peer-reviewed academic  literature to support others.

So here are a few of the sperm  quality claims that we have heard here at SciShow, and the  science, or lack of, behind them. [♪ INTRO] To start, let us go over how sperm gets made. These swimmers come from a very  specific environment in your testes. And if it gets too hot in there,  the sperm can come out with issues.

Which is why a lot of the things  in this list are about what keeps the scrotum from overheating. But  it’s not all about temperature. There are plenty of other potential  causes for messed-up sperm cells.

Like lubricants. Which you  may be using during sex, because they certainly can have upsides, But some may have a downside. It indeed does turn out that most  vaginal lubricants are bad for sperm!

And if you didn’t know that, you’re not alone. In a survey of healthcare  professionals published in 2019, none of them were aware of lubricant-related guidance for people trying to conceive. Despite the lack of general  wisdom around lube and its effects on your sperm, there is research  that suggests it can do damage.

Your little swimmers can  lose 49% of their movement control when swimming through  even a tiny amount of lube. And it’s not because they’re  slipping all over the place. Researchers think that certain  lubricants break down the membranes on a sperm’s tail, degrading  it until it’s less effective.

And it can be tough to know which ones are safe when you’re shopping, because products labeled “non-spermicidal” may still have this problem. So the authors of this study concluded that “most vaginal lubricants are sperm toxic” and are not a recommended part  of the conception cocktail. The good news is that this  study was able to identify one sperm-safe option, and  there is likely more out there.

But most lube is not great for  sperm, according to those studies. So this one? True.

While we’re talking about sex,  let’s tackle another rumor. Some people say that ejaculation  too recently before sex leaves you with semen that  will not get the job done. This is true at least  sometimes, but kind of depends on what you mean by “recent” or “frequent.” One study found that sperm counts and motility were reduced in second and third ejaculations, so rounds two and three would be less… potent.

However, a different study  found exactly the opposite. Not only were round two swimmers more concentrated, they had  higher motility as well. So it’s hard to say for sure what’s going on here.

Everyone who makes sperm  does it at a different rate, which could be part of the discrepancy. In any case, sperm count builds  back up again after several days, although the number of days  really depends on the individual. Some people need about a week  between rounds to get things back to normal.

For others, two  times a day might be totally fine. So this one? Mixed.

Now that we know to skip  the third round of the day and avoid lube if you can  while still enjoying the ride, we can get to the question on  everyone’s minds: boxers or briefs? In terms of preference, a  2016 study in the US found that people are almost evenly  split three ways across wearing boxer-briefs, boxers, and briefs. There is a slight preference for boxer-briefs and very few people wear briefs at night.

But other than that, they’re  worn at similar levels. And it could matter which one you prefer because boxers are looser, and therefore cooler. At least temperature-wise.

I have  no clue which is more fashionable. The thing is, that temperature  benefit is less than one degree. An analysis of semen quality based  on sperm shape, sperm maturity, and DNA found no consistent  effect of underwear style.

While there were a few  differences in the sperm shape, some were beneficial and others were detrimental. So they didn’t translate to  any ability to predict who would end up having babies and who wouldn’t. Which means this one is busted.

While the underwear you choose  probably won’t affect your fertility, other choices you make can crank  the heat too high for sperm. Like when you use a laptop. Or rather, how you use a laptop.

Holding your laptop where the name says to, on your lap, increases the heat in your scrotum and can cause sperm defects  in as little as 11 minutes. But that heat is mainly from  your body, not the computer. See, to balance a laptop  in place, most people need to keep their legs together.  And the lack of airflow and concentration of body heat  that this position causes is enough to spike the temperatures that could be dangerous for your swimmers.

But there’s a way around it. A small study found that manspreading and adding a pad on your lap to hold your computer up could nearly triple the amount of time it takes to elevate scrotal temperature  by 1 degree Celsius. And a lot of studies support  the idea that you can’t make new sperm as effectively at  even just one degree hotter, so that really makes a difference.

So studies like this one  demonstrate that how you sit matters at least a little, and that there’s  a medical benefit to manspreading. But you don’t need to go all the way wide, especially if you’re on public transit. This one is true.

As it turns out, it’s not just how you sit that can make a difference in your sperm quality. What you’re sitting on matters too. A small Finnish study compared  six commonly used chairs to see which, if any, made a difference  in how hot your undercarriage gets.

They found that it only took 20 minutes  to significantly increase scrotal temperature by 3 degrees Celsius  in multiple kinds of chairs. The one that didn’t end up  with that temperature increase? The saddle chair.

It might be better at dissipating the heat because the shape of the saddle chair  doesn’t support your scrotum. So some chairs are better than others for keeping things cool down there. True.

The type of chair isn’t the only factor. Some research suggests that how  cushioned it is could also matter. So in a small South Korean experiment, men sat on chairs with varying cushion thickness and their scrotal temperature  was measured for two hours.

The question was whether or not the insulation from extra cushioning interferes  with heat dissipation. And it did not. With the thickest cushion  tested coming in at 8 cm, average scrotal temperature increased anywhere from 0.85-1.6 degrees Celsius.

Which still left them within  the normal temperature range. One cushion didn't change  average teste temperature at all, and that wasn't even the thinnest cushion. So you can’t necessarily make a statement about thicker cushions leading to hotter testes.

That one is just not true. And now! For a note from our sponsor.

Thank you for watching this SciShow video. And thank you to this months Presidents of Science McLaren Stanley and Charlie  Stanley for supporting it. If you saw a graphic you liked  or learned a new fun fact in this video you can thank Presidents Stanley for commissioning all of that stuff.

Okay so it’s not that official. We can kind of make whatever  we think y’all will like. And that’s because our Presidents are so cool, and give us the funding and freedom to do that.

You can learn more about our presidential fund at Patreon.com/SciShow. With the emergence of COVID as a global pandemic, lots of people were left wondering  what it could do to the world. And one side effect that you might not have thought to worry about is sperm count.

Since a lot of illnesses result in  fever, the idea of getting sick and then having your sperm pay the price  is not new or specific to COVID. Generally, a fever has been  associated with short term reversible decreases in sperm output and  movement, among other factors. But some experts have suggested  that these effects on sperm might be worse in COVID cases  because the fever lasts longer.

There may be long term effects, months after the fever, according to some studies. So this rumor is sounding true, at  least with the info we have now. Just one more reason to get vaccinated!

True. Okay, so maybe it’s not that surprising  that getting sick isn’t great for our sperm. But surely stuff  that’s good for our health would be good for our sperm  too, right?

Like bicycling. Some researchers have proposed  that depending on how you ride your bike and for how long, you  can put too much pressure on your perineal region and crunch a nerve  or cut off circulation down there, leading to the dreaded numb  penis, among other problems. Wait a second, what?

This is based off of old research,  including a survey of 160 bikers. 33 of them said they had a numb  penis after riding their bikes, and 10 of them said the  numbness lasted over a week! I would quit! More worryingly, the authors of the study said that 21 were impotent after riding.

For 11 of them, it lasted for more than a week. And for 3 of them, it lasted  for more than a month! The longest effect in this survey was one cyclist whose impotence lasted for 8 months.

That’s pretty scary, but that  participant might be an outlier, since most of the participants did not go numb. And most of the people who did reported that things went back to normal within the same day. Also, there seem to be things  you can do to avoid this problem.

Research suggests that a good  bike fit and a saddle that doesn’t protrude too far  forward can reduce perineal pressure by 66% and drastically reduce numbness. The difference-maker is how pressure gets redistributed across short nose seats. So this particular rumor  can be true depending on how you ride your bike.

The question  is whether there’s really anything special about cyclists  compared to other athletes. When compared to soccer players, or footballers, as this European study called them, there was no statistical difference in sexual performance. While way more of cyclists had perineal numbness, it didn’t affect their erectile function scores.

So this rumor may be true, but there may be other sports with similar issues too. Mixed. Now if you’re trying to save your  sperm, avoiding all sports all together might not be the answer  either, since excess weight is another factor that can harm your sperm quality.

Inactivity is linked to excess  weight, which can lead to oxidative stress, or a buildup  of free radicals in the body. That buildup can damage the DNA in your sperm and has been associated with infertility. I know, that’s a lot of maybes that have to be true for the whole chain to link up.

And that may be why the literature  is ultimately pretty mixed on whether or not obesity has  consistent effects on sperm. But the most balanced publications seem to indicate a small measurable effect. One study found that fat  itself wasn’t correlated with sperm issues, but an increased  body mass index was associated with lower levels of a specific  hormone called Inhibin B, which can be a sign that sperm  formation isn’t going well.

That said, the effect of  weight on sperm may also have to do with heat,, as excess  fat in the thighs and lower abdomen could provide insulation to the scrotum. Even if the effects are somewhat  small, the research does support that obesity is  correlated to worse sperm counts. True.

Another lifestyle change that could make a difference for your sperm is drinking. Several meta-analyses concluded that alcohol consumption is associated  with reduced semen volume. And oxidative stress may be  the culprit in this case too.

Or it could come down to hormonal effects. One of the meta-analyses found a decrease in some of the main hormones regulating reproduction, and that could reasonably be  linked to decreased fertility. We know that excessive alcohol intake  is bad for your health in a lot of ways, so it does make sense that  it’d be bad for your sperm, too.

The bright side to this story  is that you don’t necessarily need to cut out all alcohol to  improve your reproductive output. The paper concluded that  there was a bigger difference between daily and occasional  drinkers than there was between occasional drinkers  and non-drinkers, so it doesn’t seem like the occasional cold  one will do too much harm. So, this one’s mixed.

When researchers wanted to study this last rumor, they inadvertently solved an  age-old debate that has plagued the Internet for forever:  How would a dog wear pants? Dogs are mammals just like us. So when one research group  wanted to know how fabrics like polyester affect sperm quality,  they turned to dogs for the answer.

They put polyester underpants on some dogs, cotton ones on other dogs, and let the final group of dogs run around naked like dogs. The dogs wearing polyester pants had damaged sperm after two years of being fashion icons, while the other two groups of dogs were both fine. Then in a followup study conducted in the ‘90s, those researchers asked men to  wear a polyester sling around their reproductive organs, because  science is weird sometimes.

After one year, these men had  smaller testicles and even had degeneration of their seminiferous tubules, the place where sperm cells are made. More importantly, all participants  lost fertility while wearing the sling. After an average of 139 days, all 14 participants became azoospermic, meaning  they were shooting blanks.

These researchers even suggested  that polyester slings could be a safe method of contraception,  because the effects were reversible. This might happen because polyester generates an electrostatic field across your scrotum. They could even pick up  that electrostatic response, using something called a kilovoltmeter.

Which sounds to me like polyester pants really can impact your sperm counts! True! I’m surprised.

And for the answer we’ve all been waiting for, the dogs wore their pants on their back legs only! Case closed! So there we have it, the truth  and the myths around what can impact your sperm quality  according to current science.

Whether you’re trying to conceive or  barely think about your little guys, it’s always good to be able  to separate fact from fiction. Especially if doing so means  putting dogs in funny outfits. [♪ OUTRO]