In one sentence, the biology of sex may seem even simpler than using the “birds and bees” metaphor. Sperm gets ejected from the penis, enters the vagina, and swims up the reproductive tract until they reach the egg to fertilize it.

But it isn’t quite that simple.

Barely 300 years ago, it was considered a major scientific breakthrough when scientists came up with the idea that a fully formed, tiny human inhabited the head of each sperm — totally debunked and untrue.

Fortunately, as the human body has evolved over thousands of years to maximize fertility potential, so has our scientific understanding about sperm. But many of us still believe some pretty unscientific, long-standing sperm myths. Here are twelve of the most common ones.

The common tale is that millions — anywhere from 20 to 300 million, to be precise — of heroic sperm swim in competition with each other to be the lucky little swimmer that penetrates the egg.


First, sperm don’t really swim straight — for the most part. Often sperm movement ability, known as motility, is classified into one of three groups:

  • progressive motility: actively moving in straight line or large circles
  • non-progressive motility: any other pattern except forward
  • immotile: not moving

In an essay for Aeon, Robert D. Martin described the route as “more like a challenging military obstacle course” and less of a standard race. And even then, sperm require more than a little boost from the female productive system to make sure they get to the finish line.

In fact, most of the motility work is done by the uterus muscles. It coaxes the sperm along to the fallopian tubes, towards the egg.

Thicker semen doesn’t necessarily mean thicker sperm. Usually it means there’s a high concentration of sperm or a high number of irregularly shaped sperm. They still need help from the female reproductive system to stay safe.

When sperm enter the vagina, they come into contact with cervical mucus. The cervical mucus does two things: protects and rejects. It protects sperm from the vagina’s acidity as well as rejects sperm whose shape and motility would otherwise keep them from reaching the egg.

How the female reproductive system helps sperm:

  1. The cervix — the tissue between the vagina and uterus — walls widen.
  2. Crypts, or cervix glands, grow in number and increase in size to store more sperm.
  3. The cervix’s mucus barrier thins out so it’s easier for sperm to pass through.
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Not always! Lifespan depends on where sperm land after ejaculation.

Sperm that make it into the vagina after ejaculation can live up to five days. This is due to the protective effects of cervical mucus and cervical crypts.

But if sperm have a chance to dry out, they basically die. Ejaculated sperm that land on cold, dry objects may die after a few minutes — although very rarely they may last a whole 30 minutes. They may die even faster in a hot bath or a hot tub due to the heat or chemicals in the water.

It’s a pretty long journey to the egg. During intercourse, when sperm leave the penis, they don’t head straight to the uterus.

In this course, some sperm attach to oviduct epithelial cells in the fallopian tubes or get stored in tiny chambers called crypts until fertilization primetime: ovulation.

The path to fertilization: where sperm need to pass before reaching the egg

  • vagina: the first and outermost portion, on average three to six inches
  • cervix: a small, cylindrical canal that connects the vagina to the uterus
  • uterus (or womb): where a fetus grows during pregnancy
  • fallopian tubes: two tubes that connect the uterus to the ovaries, allowing sperm to move toward egg cells and fertilized eggs to move into the uterus
  • ovaries: two organs that produce egg cells that can be fertilized to become fetuses
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One of the oldest persisting myths is that while there are a limited number of eggs (which is true), sperm is available in a lifetime supply.

Not so fast.

Sperm production, or spermatogenesis, does take place indefinitely, but the quality and motility of sperm declines with age.

Older men are also more likely to pass genetic mutations onto their children, about four times faster than a woman would, according to an Icelandic study.

A 2017 study of 1.4 million people in Sweden found a consistent linear relationship between a man’s age and the likelihood that his children would be born with a genetic mutation that neither parent has.

Supposedly, tight undies decrease sperm count, while loose boxers keep everything at just the right temperature for sperm production.

But underwear has (almost) no effect on your sperm.

A 2016 study found little difference in sperm count based on underwear choice. But a 2018 study made scientific waves when it found that men who wore boxers had 17 percent more sperm than men in briefs.

But the 2018 study authors warned that their results didn’t account for other factors that affect sperm production, such as type of pants or what fabric undies are made of.

And get this: The body may compensate for extra testicle heat by releasing a little extra sperm-producing follicle-stimulating hormone.

So, boxers are only a little bit more sperm-friendly. Wear what makes you comfortable.

Far from it.

Most sperm never make it to the egg for a number of reasons. To be considered fertile, not even 100 percent of sperm need to be moving — as long as 40 percent are motile, you’re fertile!

And of that 40 percent, not all make it to the egg.

The shape has a lot of say in success. Having multiple heads, weirdly shaped tails, or missing parts can make sperm simply unfit for the journey through the female reproductive tract.

And even healthy sperm don’t always make it through the competition. Sperm can pass right through the oviduct and end up in a woman’s interstitial fluid surrounding the internal organs. That’s right, sperm may literally float around in the body, never to fertilize.

False! Mostly. Biologically speaking, pre-cum shouldn’t contain sperm — but sperm left over in the urethra, the tube through which both urine and semen are ejected, can get mixed in.

Sure, there aren’t as many as in new semen, but a 2011 study showed that nearly 37 percent of pre-cum samples collected from the study’s 27 subjects’ contained a significant amount of healthy, motile sperm.

And a 2016 study of 42 men found that at least 17 percent of pre-cum samples were full of active, mobile sperm.

So even if you’re using the pull-out method, there’s a small chance that some sperm can get loose and cause a pregnancy.

Quite the opposite.

Having a high semen volume, which counts sperm in a single ejaculation, is good but there’s a point where the returns start diminishing. The higher the sperm concentration, the more likely that multiple sperm may fertilize the egg.

Normally, only a single one-celled sperm cell is allowed to fertilize one egg cell, resulting in the development of an embryo. After the first sperm breaks through a layer of proteins around the egg, this layer blocks more sperm from getting through.

But if too many sperm reach the egg, two — or more, in rare cases — sperm can break through this layer and end up fertilizing the egg. This is called polyspermy.

By delivering extra genetic material to the egg, this increases the risk for DNA mutations, brain conditions such as Down syndrome, or potentially fatal defects in the heart, spine, and skull.

Keep this in mind if you and your partner decide to use in vitro fertilization (IVF) to get pregnant. Because IVF bypasses many reproductive functions that limit how many sperm get to the egg, your semen doesn’t need to have millions of sperm to be fertile.

This is a popular myth that’s probably been joked about constantly. But you’d have to ingest more than 100 ejaculates to see any nutritional benefit from it.

While it’s true that semen is composed of ingredients like vitamin C, zinc, protein compounds, cholesterol and sodium, claiming sperm contributes to your daily nutritional value is false advertising.

Plus, some people actually have allergic reactions to semen, so ingesting it isn’t always recommended.

It’s not just pineapples that people say are supposedly good for semen flavor, but none of the tales are based in science.

The first thing to learn here is that semen scent and taste, like that of many of your bodily fluids, are influenced by overall genetics, diet, and lifestyle. Just like everyone’s breath smells different, everyone’s cum has its own unique aroma.

The second thing is that, while no foods or liquids may noticeably alter semen scent, following a diet rich in nutrients like vitamin C and B-12 can have positive effects on sperm count, morphology, and motility.

Some of these myths go way back to (false) notions of sperm exceptionalism, but many of them also obscure the fact that conception, like sex, is much more of an active partnership.

Believing these myths can also lead to many inaccurate or toxic presumptions. For example:

  • false portrayals of women as being passive receptacles of sperm rather than equal collaborators in sexual intercourse
  • feelings of inadequacy for having a low sperm count
  • blaming one partner or the other for not “pulling their weight” when trying to have a baby when so many other factors must be considered

Sex and conception aren’t a competition or a feat of strength: They’re a team activity in which all genders have equal footing, whether you produce sperm or eggs. It’s a two-way street, but no one should feel like they have to walk it alone.

Tim Jewell is a writer, editor, and linguist based in Chino Hills, CA. His work has appeared in publications by many leading health and media companies, including Healthline and The Walt Disney Company.