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A weekly show where knowledge junkies get their fix of trivia-tastic information. This week, Dr. Aaron Carroll (http://www.youtube.com/thehealthcaretriage) debunks some common myths about sex.

Buy Aaron's book here: http://www.amazon.com/Dont-Put-That-There-Debunked/dp/1250042267/ref=tmm_pap_title_0

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  Introduction (00:00


Hi, I'm Aaron Carroll. You can usually find me here at Healthcare Triage but today we're gonna head over to the salon, for Mental Floss where I'll be talking to you about 20 myths and misconceptions about sex.

Look, fair warning here, this is an episode about sex. If you think that's inappropriate or it's not your thing, probably a good idea to turn this off now.

 01 (00:16


Did you know that it's a myth that there is any correlation between penis size and shoe size? There have been many studies on this, amazingly enough, and they fail to find any link between the size of a man's shoes, and the size of a man's stretched or erect penis. There is also no relationship between his penis and the size of his hands or ears. Or anything else for that matter. Looking at his shoes will only tell you about his taste in footwear. And that's the first of many misconceptions about sex I'm gonna debunk today.

[Intro plays.]

  02 (00:49


It's a myth that the average man has a seven inch penis. Let's be honest, to study this correctly you can't ask men how big their penises are, you have to get in there and measure yourself. We found fifteen studies that looked at stretched penile length and most of them had an average around 5 inches. Here in Indiana, the Kinsey Institute studied more than 1,600 men and found an average erect penis size was about 5.6 inches. Interestingly, erections brought about by oral sex were larger than erections brought about by manual stimulation. Is that cause oral sex causes bigger erections, or is cause bigger penises get oral sex? We have no idea.

  03 (01:24


It's a myth that wearing a condom makes you last longer. In a study of 500 men from Europe and America their "intravaginal ejaculation latency time" was 5.4 minutes. They literally clocked these men with a stopwatch. Men 18-30 years old lasted the longest, at 6.5 minutes on average. Dropping to only 4.3 minutes for men over 51. Wearing a condom made no difference. Nor did whether the men were circumcised.

Here Clark Kent's super speed backfires, Aquaman wins.

  04 (01:51


It's a myth that you can build up a much bigger load. I'm not sure why so many people care about this but here we go. In 2005 a study of more than 6,000 men who had provided about 9,500 "samples" was published. Men who waited a week had an average ejaculate volume of 3.7 ml. Men who had sex the day before, had a volume of 2.3 ml. That's a difference of less than a 1/3 of a teaspoon. But even men who came earlier that day still produced 2.4 ml, so we can't imagine that waiting is worth it.

  05 (02:21


It's a myth that men want blondes more than brunettes. Sure, there have been some local studies that point to the fact that men may say this, but they're usually in places where blonde hair is less common. In areas where blonde hair is more common, the preference is not as clear. There's also no correlation in studies between women having blonde hair and having more sexual partners, more sex, or more orgasms.

  06 (02:42


It's a myth that most women are going hairless these days. Yes, it's true that playboy centerfolds are more likely to have little or no pubic hair in recent years, but that's a skewed sample. A 2010 survey of more than 2,400 women found that only 11% of women age 18-68 remove all of their hair most of the time. 20% removed no hair at all, and only about a quarter removed their pubic hair some of the time. Going bare is somewhat related to age, with 21% of 18-24 year olds shaving it all off, versus 9% of women in their 30's or 2% of women over 50. Bottom line though, is that the majority of women of all ages keep some hair down there.

  07 (03:21


It's a myth that bigger breasts are less sensitive than smaller breasts. Some people have argued that bigger breasts have longer nerves to get to the skin, and that this makes them "feel" less. Of course, then, taller women would have less sensitivity, too, and no one makes that argument. The evidence for this comes from studies that ask women if they could feel hair-like filaments of different sizes on their breasts. There were differences, but no woman ever defined sensitivity during sex as the ability to feel a single hair. Besides no one argues that men with smaller penises derive more pleasure than men with large penises.

  08 (03:52


It's a myth that sex is great exercise. Yeah, it burns off some calories, but most people aren't active for that long. 30 minutes of sex might burn of 85-150 calories but remember the average intravaginal ejaculation latency time I mentioned before? Not even close. The time that sex is aerobic, where your heart rate goes up is even shorter.

  09 (04:14


Despite what you've learned from our highly scientific competitor, Mad Men, it's a myth that all men cheat, or that there's a difference between men and women. If you define cheating as intercourse, then yeah, men cheat more often. If you broaden it to include other acts, then women cheat pretty much as often as men. Surprisingly, age doesn't seem to be a factor, either. The most comprehensive study we've seen showed that 23% of men, and 19% of women, had cheated in their current relationship. The biggest predictor was being unhappy or incompatible in terms of sexual attitudes or values.

  10 (04:45


It's a myth that men peak sexually long before women. What does peak mean, anyway? If you define it to be the frequency of sex, then both men and women are likely to go without it for a whole year during their 20's. If we define it by masturbation, they're both most likely to do it in their late 20's. If we define it by oral sex, men are most likely to get it in their late twenties and give it in their 30's. Women are most likely to give and receive it in their late 20's. If we define sex at least four times a week, it's 30's or 40's for men, and late 20's for women. There's no metric that makes this myth true.

Speaking of sexual peaks, did you ever wonder if Spiderman was a metaphor for going through puberty?

 11 (05:21


It's a myth that young men are more likely to ejaculate prematurely. If we define that as climaxing too early then studies have shown that 30% of 18-29 year olds have an issue. But so do 32% of men in their 30's, 28% of men in their 40's, and 32% of men in their 50's. For most men, it's a transient issue that goes away. For men with severe and lifelong premature ejaculation, it actually worsens as men age.

  12 (05:47


It's a myth that men think about sex every 7 seconds. This one defies belief, it would be, sex ... sex ... sex, all day! That would be more than 57,000 times a day! It's pretty much every time you take a breath. Over 40% of men report thinking about sex only a few times a month or a few times a week. 4% of men, they think about sex less than once a month. There's no truth to this one at all.

 13 (06:17


It's a myth that married people don't masturbate. Lots and lots of people masturbate. A study of college students found that 98% of males and 44% of females reported having masturbated. Males averaged 12 times a month and females averaged 5. A study of married people, found that 85% of men and 45% of women had masturbated in the last year.

 14 (06:38


It's a myth that dead males can develop erections. Who comes up with this stuff, anyway, do an internet search and you're bound to come up with a news story about a woman in Missouri who worked in a mortuary and was arrested after becoming pregnant from a cadaver she, well, worked on. It's a hoax. What is also a hoax is the idea that a cadaver could "develop" an erection. Can't happen. If you die flaccid, you're flaccid for good. It is possible to die with an erection, though. And keep it. It actually occurred pretty often in men who died by hanging. You still can't cause a dead body to ejaculate, though.

  15 (07:11


It's a myth that only males have wet dreams. First of all let's stipulate that a wet dream is a state of sexual arousal, while asleep, that results in orgasm that wakes you up. More than one study has found that about 40% of females report having had this happen to them. About 30% of females report this happening in the last year. The numbers for men are higher, but women ain't doing too badly.

 16 (07:32


It's a myth that masturbating will make you go blind. I mean, come on. If this were true YouTube would be a total waste of time because almost none of you would be able to see the videos. This is just totally untrue. But here's a fun fact, John Harvey Kellogg, was a famous nutritionist and sexual advisor, he developed a number of foods including his eponymous corn flakes to reduce sexual desire and stop masturbation. I don't think they work.

  17 (07:58


It's a myth that the pill will make you gain weight. When the pill was first developed, it contained very very high levels of both estrogen, and progesterone, but the pill as it exists today is much more refined and contains far lower levels of hormones. A meta analysis by the Cochrane Collaboration found 49, yes, 49 studies that compared the pill to a placebo, and other pills, with respect to weight gain. None of the studies that compared the pill to placebo, showed that birth control pills cause weight gain. I'm not saying you're guaranteed to not gain weight if you go on the pill, but it's likely not because of the pill.

This pill full of candy will make you gain weight. It still won't make your kids hyper, though.

  18 (08:35


It's a myth that you can game having a boy or a girl by how you have sex. You just can't. Some people say that X sperm are bigger than Y sperm, because the X chromosome is significantly bigger than the Y chromosome. Therefore, if ejaculation occurs further from the cervix, Y sperm have a better chance of overtaking the X sperm and making it to the egg first. So if you want a girl, go for a deep ejaculation. If you want a boy, do the opposite. Another explanation has it that X sperm are hardier than Y sperm. So if you ejaculate farther from the cervix, X sperm are more likely to make it all the way to the egg first. If this is true, if you want a boy, go for a deep ejaculation. If you want a girl, do the opposite. Or just recognize that all of this is ridiculous.

  19 (09:16


It's a myth that you don't need the HPV vaccine until you're having sex. First of all, you need to be fully vaccinated before you're ever exposed to HPV for the vaccine to work. And that takes time. So once you've had sex, it may be too late, HPV is really common. So is sex.

By the end of their teenage years, more than 3 quarters of all  adolescents have engaged in sexual intercourse. More than 2 thirds of them have had sex with at least 2 people. More than 6 percent of children in the United States have sexual intercourse before the age of 13, and younger kids are the least likely to use protection. The HPV vaccine is about prevention, get it early.

  20 (09:52


And we return to the salon to talk about the myth that the HPV vaccine encourages girls to have sex. This has been studied through a cohort of almost 1400 girls, 493 received the vaccine. Researchers followed them for 3 years after immunization to see if there were any differences in sexual outcomes. There weren't any. The girls who got the vaccine didn't get any more sexually transmitted infections, they didn't get pregnant more often, and the didn't seek contraceptive counselling more. The HPV vaccine only protected them.

  Closing (10:20


Thanks for watching mental_floss on YouTube, which is made with the help of all these nice people. Again, I'm Dr. Aaron Carroll and hey, if you like this episode, you might want to buy our recently published book "Don't Put That In There!" and 69 other sex myths debunked. You get it at book stores everywhere and links are in the text below. Buy a copy, I'd really appreciate it.

You can also find me regularly on healthcare triage filmed right over there. We talk about everything health and health policy related, links also down below.

Every week we endeavour to answer one of your mind blowing questions. This week's question comes from meshay13 who asks "Why is there no metric version of time, like a base 10 time system or something?". Well meshay there is, but no-one uses it. It uses base units that are somewhat equivalent to decimal divisions of the day like 1/10th or 1/100th, 1/1000th etc, lots of different names have been proposed for these divisions, like Tick, Mec, Ki, Cron and Moment. In 1897 in France, a committee proposed switching to metric time, but the idea never gained popularity.

Thanks again for watching, don't forget to be awesome, remember to wear a condom.