Many of us still believe some pretty unscientific, long-standing myths about sperm, semen, and male fertility. From sperm speed to nutritional makeup, here are 12 of the most popular urban legends.

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 reaching an egg to fertilize.

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 of sperm.

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 an egg. Nope.

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: Sperm actively move in straight lines or large circles
  • Non-progressive motility: Sperm move in any other pattern except forward
  • Immotile: Sperm do not move

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 reproductive system to reach 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 toward an egg.

Thicker semen doesn’t necessarily mean thicker sperm. Usually, it means there’s a high sperm concentration or a high number of irregularly shaped sperm.

Sperm that enters a vagina comes 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 of a certain shape and size (morphology) or motility that would otherwise prevent sperm from reaching an 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.

Not always! Lifespan depends on where sperm land after ejaculation.

Sperm that make it into the vagina after ejaculation can live up to 5 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, sperm may last a whole 30 minutes.

Sperm 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 an egg. During penis-in-vagina sex, sperm don’t leave the penis and head straight to the uterus.

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 an egg

  • Vaginal canal: The first and outermost portion, which is about 2–4 inches (7–10 centimeters) long
  • Cervix: A small, cylindrical canal that connects the vagina to the uterus
  • Uterus: Where a pregnancy develops
  • 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

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 decline with age.

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

A 2017 study of 1.4 million people in Sweden found a consistent linear relationship between a male’s age and the likelihood that their 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 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 people who wore boxers had 17% more sperm than people in briefs.

However, the 2018 study authors warned that their results didn’t account for other factors that affect sperm production, such as the 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 an egg for a number of reasons. To be considered fertile, not even 100% of sperm need to be moving — as long as 40% are motile, you’re fertile!

And not all 40% will make it to an egg during penis-in-vagina sex.

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 through the oviduct and end up in interstitial fluid surrounding the internal reproductive 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% of pre-cum samples collected from 27 subjects contained a significant amount of healthy, motile sperm.

A 2016 study of 42 participants found that at least 17% 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.

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 multiple sperm may fertilize an 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 an egg, this layer blocks more sperm from getting through.

But if too many sperm reach an egg, two — or more, in rare cases — sperm can break through this layer and fertilize it. This is called polyspermy.

Delivering extra genetic material to an egg increases the risk of DNA mutations, brain conditions such as Down syndrome, or potentially fatal defects in the heart, spine, and skull.

Consider this if you or a partner use in vitro fertilization (IVF) to get pregnant. Because IVF bypasses many reproductive functions that limit how many sperm get to an egg, 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 on science.

The first thing to learn here is that semen scent and taste, like many bodily fluids, are influenced by overall genetics, diet, and lifestyle. Just like everyone’s breath smells different, everyone’s cum has its 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 vitamin B12 can positively affect 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 penis-in-vagina sex
  • Feelings of inadequacy for having a low sperm count
  • Blaming a partner 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 participants have equal footing, regardless of whether you contribute sperm, eggs, or surrogacy.