Read an Excerpt

Don't Put That in There!

And 69 Other Sex Myths Debunked

St. Martin's Press

Penis Size Matters

One of our friends debunks the myth this way: "It's not the size of the wave, but the motion of the ocean." There are a lot of different ways to phrase this, but it comes down to one important question: Does it matter how big the guy's penis is? We will start by looking at whether penis size matters to men who have sex with women, then whether it matters to the women themselves, and then whether it matters to men who have sex with men.

If you ask your friends, you might hear all kinds of answers to this question. Some claim that size does not matter at all as long as the man knows how to use their penis well. Others swear that the best sex of their lives was with a particularly well-endowed partner. And some will say that sex with an exceptionally large penis was not enjoyable, and even painful. Both popular opinion and surveys suggest that men are very concerned about the question of how big they are and how the size of their penis compares to other men's penises.

Scientists have looked at the influence of penis size on all sorts of things — from height and body fat to sexual satisfaction and the risk of having various infections. The studies tell us that penis size does matter, but not necessarily in the ways that you might think.

A huge Internet survey of more than 50,000 heterosexual men and women investigated penis size and satisfaction. In this survey, most men reported that they had an average-sized penis (66 percent), while 22 percent said their penis was large and 12 percent rated it as small. No actual penis sizes were measured, so this study relied only on what these men said about themselves. (Remember, they might not have the right idea about what an average penis size really is!) About half of the men (55 percent) were satisfied with their penis size, but 45 percent wanted to have a larger penis and 0.2 percent wanted to be smaller. In contrast, 85 percent of women reported being satisfied with their partner's penis size. This suggests that size is less important to women, or that they are more likely to be satisfied with their partner's penis size, than he is with his own size.

In this study, reporting that you had a big penis was linked to other body traits that are generally thought to be good. The self-reported penis size correlated positively with being taller and with having less body fat. The men reporting having larger penises also reported being more attractive. While some people might call that good luck or good genes — whatever it is that makes you both well-endowed and handsome — this finding could also reflect very confident individuals who think that everything about themselves is great, from how handsome they are to how big their penis is. This is one of those unexpected ways in which penis size might matter. How you see your penis might be correlated with how you see the rest of you.

Other studies have looked at how penis size, body shape, and height might be related to each other. Scientists have wondered whether evolution pushed these traits together because women might have considered all of them when they were considering their mating options. An evolutionary force might be at play if women were making their decisions about who to mate with based on whom they found the most attractive. If women found penis size very attractive, then women might be more likely to pick men with bigger penises, and then humans might be pushed toward having bigger and bigger penises.

Along these lines, scientists wanted to assess how much penis size plays into women's ideas about who is attractive. To do this, they set up studies where women evaluate life-sized digital pictures of men of various proportions. It turns out that penis size, body shape, and height are all significant factors in who women think are hot. Increasing penis size in these digital men did increase how often women thought they were attractive, but the effect got smaller and smaller past a certain point. Penis size actually had a stronger effect on attractiveness in taller men than in shorter men, and the same was true for men with a more masculine body shape (which is defined as having wider shoulders and narrower hips). This means that increasing the size of the penis on a taller man got them a higher rating of attractiveness than increasing the size of the penis by the same amount for a shorter man. It turns out that height and penis size matter about the same in these judgments of attractiveness. Larger penis size and taller height had almost the exact same influence on a woman's rating of the man as attractive.

Of course, just because penis size may factor into a woman's judgment of how attractive someone looks does not mean that this will influence their decisions about their partners. After all, 85 percent of the women in that big survey did say they were satisfied with their partner's penis size. Plus, an important question remains: Does penis size actually influence sexual pleasure?

One study does suggest that penis size may make a difference for women's orgasms. A study of 323 women investigated how often they had penile-vaginal intercourse (that means sex with a penis in the vagina), vaginal orgasms, and clitoral orgasms. (To read more about the many ways women can have orgasms, see the fun chapters on whether a woman needs her clitoris stimulated to have an orgasm and whether women have orgasms through anal sex!) The study's whole goal was to figure out whether having sex with someone with a longer penis made you more likely to have a vaginal orgasm. According to this study, it kind of does!

It turns out that women who prefer deeper penis stimulation are more likely to have vaginal orgasms. This was not a study that could show cause and effect. The link between long penises, deep stimulation, and vaginal orgasms could mean that a longer penis gives you more vaginal orgasms, but it also could simply mean that women who say they prefer longer penises are more likely to have vaginal orgasms. It does not mean that the longer penis is more likely to cause a vaginal orgasm, but that the women who are having those vaginal orgasms think that the longer penis might be a good thing. In this study, these women also placed less importance on noncoital sex (sex that did not involve the penis being inside the vagina). Still, this suggests that there might be a subset of women for whom penis length makes a difference in their sexual experience.

Despite this limited evidence that size might affect some women's experiences, having the right moves might make up for any perceived deficiencies. Sex therapists and specialists can teach you something called "Coital Alignment Technique," which has been evaluated in a series of controlled studies. In these studies, certain positions or "ineffective" intercourse techniques are shown to cause sexual problems like women not being able to have orgasms during penile-vaginal intercourse or premature ejaculation. However, using the "Coital Alignment Technique" increases the odds of the woman having an orgasm during penile-vaginal intercourse. (In other words, these moves alone could lead to vaginal orgasms, regardless of the penis size.)

Find yourself wondering just what this "Coital Alignment Technique" is? It sounds a little complicated, but here is what it entails: A man lies right on top of a woman, but moves himself far enough up along the woman's body that his erection is actually pointing down, so that the top side of the penis presses against the clitoris. To thrust deeper inside, the man actually moves his body down compared to the woman, and then moves back up as he withdraws. The man and woman are supposed to focus on the movement of their pelvises and not on support or movement using their arms or legs.

Good luck with that!

Here's another interesting question: Does penis size matter when it comes to men who have sex with men?

There is not much scientific literature describing what penis size means among men who have sex with men, but one study surveying 1,065 men who have sex with men did evaluate how the men's perception of their penises influenced other characteristics of their sexual health.

In this group, 7.1 percent reported their penis size was "below average," 56.0 percent described it as "average," and 36.9 percent called their penis size "above average." Among the entire group of men, reported penis size did not seem to make any difference for the number of sex partners, frequency of sex, condom use, or likelihood of having HIV or other sexually transmitted infections including gonorrhea, chlamydia, syphilis, urinary tract infections, or hepatitis.

In contrast, men who reported an "above average" penis size were statistically more likely to be satisfied with their penis size and less likely to lie about its size. They were also more likely to report two things that no one wants to have — genital warts and herpes. The correlation between having a larger penis and having more genital warts or herpes infections is interesting because both of these infections are caused by viruses that can be passed from one person to another if any affected part of the penis or the skin around it isn't covered by a condom. This connection made the authors of the study wonder whether the larger penis size meant these men had more issues with condoms slipping or breaking, both of which could leave contagious skin exposed and increase the chance of infections.

Among men who have sex with men, their perceived penis size might also impact the sexual position they assume during sex, as well as their psychosocial adjustment. In this study, men who reported having "below average"-sized penises were significantly more likely to identify themselves as "bottoms," meaning that they were the ones on the receiving end of anal sex. In contrast, the men who said they had "above average"-sized penises were significantly more likely to call themselves "tops," meaning that they were the ones doing the insertion during anal intercourse. In addition, the men who rated their penis size as "below average" also scored significantly worse on three different measures of psychosocial adjustment. All of these findings suggest that one's perception of one's penis size among the group of men who have sex with men might play a significant role in certain sexual behaviors and psychosocial adjustment.

What do all of these studies suggest about penis size? Does penis size matter? The take-home message is that penis size may make a difference for some things (like how you feel about yourself and whether you lie about your penis), but it does not necessarily affect your partner's satisfaction with you.

Batters Up! The Battle of the 7-Inch Penis.

You cannot talk about sex for too long without getting into a discussion about penis size. A huge amount of worry, energy, speculation, and wonder seems to be devoted to whether or not a penis "measures up." From men claiming to be well-endowed, to those secretly worrying that there is just not something large enough in their pants, to endless junk e-mails about how to enlarge your penis, the size of the male member gets a lot of press.

Whether penis size matters at all is another question (keep reading for that chapter!), but many people do not even know how their penis (or another penis that they care about) compares in size to the world's penis population. Is your penis below average in size? Above average? You would be surprised at how few people can answer this question correctly.

To make a judgment on how a penis measures up, you have to think about two things: First is the size of the average penis. And, second, are you talking about a flaccid penis or an erect penis? An erection brings about a dramatic size change in penis size as it fills with blood.

Do you have your rulers ready? Figuring out the size of the average penis is more of a challenge than you might think. It is hard to get an accurate picture of penis size when you ask men to report their own measurements. Perhaps this surprises no one, but men tend to exaggerate the length of their penises, and they don't take the most exact measurements of their own members. Still, we can get some idea of average penis size when we get lots and lots of men to measure their penises.

A large Internet survey that collected penis size and other information from 2,545 men found that the average length of the erect penis was 6.4 inches (with a standard deviation of 1.2 inches). These averages were based on men's own measurements of their erect penises.

In another study done by Indiana University researchers at The Kinsey Institute, the average erect penis size among 1,661 American men was 5.6 inches. Interestingly enough, in this study, the average size was different based on how the man got the erection. The men who had received oral sex and then measured their erection reported larger sizes than the men who got their erection from self-masturbation or hand stimulation by a partner. You can't really figure out why these differences exist from this type of study. It's possible that oral sex gives you a larger erection, but it's also possible that men with larger erect penises are more likely to get oral sex.

Based on these surveys, 7 inches should not be your benchmark for normal. In studies where men themselves report the size of their member, the average erect penis size is 5.6 to 6.4 inches. Not 7 inches. When most people talk about "average," they mean the size that is the most common. The most common measurement was more along the lines of 6 inches for an erect penis — and that still may have been an overestimation. Just because 6 inches was the most common does not mean that something else is "not normal." It's also completely normal to have penises that are smaller or larger than that.

In case you want to compare other penis measurements, in the largest survey, the average length of the flaccid, or soft, penis was 3.4 inches, the average circumference of the erect penis was 5 inches, and the average length of the head of the penis was 1.6 inches. In the study of 1,661 American men, the average circumference of the erect penis was 4.8 inches.

These surveys give us some idea of what the average penis length may be, but we still have the problem of men reporting that their members are a bit longer than they really are. To get the most accurate measures of the male member, it works best to have specialists take the measurements, and so we look to studies with measurements done by urologists.

The studies by the specialists do not include as many men, but they should give us more scientific estimates of what is average. While urologists agree that the erect penile length is the most physiologically accurate measurement, they usually use "stretched penile length" for their studies. Rather than requiring the men in the study to get an erection, the doctors doing these studies take a soft penis, stretch it out, and measure the length with a measuring tape. This stretched length is considered a good substitute for measuring the erect penis.

We found fifteen studies where objective scientists measured the stretched penile length for a group of men. In these studies, the average penile lengths found among the men ranged quite a bit, from 3.5 inches to 6.6 inches. Most of the studies (nine of fifteen) had averages in the range of 4.7 to 5.1 inches. You will note that these averages are at least an inch shorter than the measurements that men reported for themselves in the Internet survey, and the average measurements all remain less than 7 inches. In fact, the average seemed to be much closer to 5 inches.

You can put your rulers away now.

Big Feet, Big Hands, Big ...?

We started our very first book of medical myths — Don't Swallow Your Gum! Myths, Half-Truths, and Outright Lies About Your Body and Health — debunking the myth that men with big feet have big penises. No book discussing sex myths would be complete without a discussion of whether you can predict who is well-endowed. In our years of experience talking about medical myths at cocktail parties or dinners, we almost always get asked about this one. Of course, that might just be because people like to see whether Rachel blushes when she talks about penis size. (She usually does.)

Many people think that you can size up what a man's penis is going to be like by sneaking a peek at other parts of him. Large feet, hands, and noses are all rumored to tell you that the appendage in a man's pants is also going to be large. And men with small hands or feet will tell you that they hate how everyone jumps to conclusions that they will be smaller in size elsewhere.

Interestingly enough, the connection between big feet and big penises has some roots in science. A particular gene called the Hox gene plays a role in the development of the toes and fingers, as well as the penis and clitoris. If the same gene controls the growth of toes, fingers, and penises, then it might make all of them grow big (or not).

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Excerpted from Don't Put That in There! by Aaron E. Carroll, Rachel C. Vreeman. Copyright © 2014 Aaron E. Carroll and Rachel C. Vreeman. Excerpted by permission of St. Martin's Press.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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