Looking under the hood of the male body reveals more than a simple sex-driven, sperm-carrying system. In fact, scientists are still trying to decipher some of the mysteries of the male physique. Here are some wild facts, and unknowns, about a guy's body, from his other brain and the male G-spot to lactating man-breasts and more.
The sticky concoction called semen holds more than just sperm(those DNA-carrying swimmers that make a mad dash for the nearest egg). In fact, semen is a combination of sperm and fluids produced by accessory glands surrounding the penis. Its non-sperm ingredients include a mix of fructose, molecules made from fatty acids called prostaglandins, and proteins that nourish sperm and help them swim, according to the National Institutes of Health.
Additional fluids from the prostate and bulbourethral glands are slightly alkaline, or basic, reducing the acidity of any urine residue in the urethra, neutralizing the acidic environment of the vagina, and lubricating the tip of the penis for intercourse.
And turns out, what a man eats affects the quality of this semen, with a study published in 2012 in the journal Human Reproduction finding that guys who consumed more of the fat often found in fish (called omega-3s) had better-formed sperm than those who ate less of the fishy fat.
And while semen carries those critical egg fertilizers, some women are allergic to it, reacting to it with genital itching, burning and swelling. In severe cases, women may experience hives or swelling elsewhere on the body, and even difficulty breathing. A study described in 2011 at the annual meeting of the American College of Allergy, Asthma and Immunology in Philadelphia suggested a possible cure: frequent sex.
Hernias are weak areas in the outer layer of the abdominal cavity that bulge out like little balloons. There are several kinds of hernias, according to the U.S. National Library of Medicine, depending on where they form in the abdomen. But inguinal hernias, those that extend into either side of the groin, are more common in men than in women. Weak spots in the inguinal ring, the entrance to a canal housing arteries and nerves that run to the testes, allow fat or parts of the small intestine to slip through, creating a bulge in the groin (and not the good kind).
Though women also have an inguinal ring and canals, they aren't as large as those in men. Some men are born with weak spots in the inguinal ring, which can cause hernias; they can also occur because of lifting a heavy object or straining on the toilet.
Some reflexes, or involuntary muscle movements, are well known. Hit the area below your kneecap and your lower leg jerks up. But you may be surprised to find out muscles wrapped around a man's testes, called cremaster muscles, also display reflexes; though if you hit the surrounding area you probably won't get the response you're looking for.
According to the National Cancer Institute, cremaster muscles are normally responsible for pulling the testes closer to the body when it gets cold or when a man is sexually aroused. And rather than responding to the knee-jerk hammer, the cremaster reflex activates when the inner part of a man's upper thigh is stroked. The cremaster muscle contracts on the same side as the stroking, momentarily pulling the testes up toward the body.
The foreskin, which is removed during circumcision, is a double layer of skin and mucous membrane that covers the penis when the organ is flaccid. Although there is still some debate about all of the functions of foreskin, the World Health Organization (WHO) states that uncircumcised men have a greater risk of contracting HIV. Cells called Langerhans cells found in the mucous membrane of the foreskin are susceptible to HIV infection and can serve as a point of entry to the body for the virus. WHO studies have shown that circumcision reduces the risk of heterosexually acquired HIV in men by 60 percent.
One of the earliest depictions of male circumcision comes from artwork in Egyptian tombs dated to about 2300 B.C. During the Ottoman and Moorish Empires, as well as in Nazi Germany, it was seen as a mark of higher social standing. In addition to its importance in Jewish and Muslin religions, circumcision is viewed as a right of passage to manhood in some African and Oceanic societies, writes Peter Aggleton of the University of London in England in a 2007 paper published in Reproductive Health Matters. It wasn't until the late 1800s that circumcision acquired public-health interest. It was touted as a cure for anti-social behavior and paralysis and blamed for decreased sexual pleasure. More recently, circumcision has been shown to reduce the risk of contracting HIV in men.
Men don't typically produce milk from their breasts. But under certain circumstances, they can. For instance, extreme starvation, hormone treatments for various health problems, and mechanical stimulation, can lead to lactating lads. This phenomenon is different from gynecomastia, male breast enlargement due to imbalances in testosterone and estrogen. Noted scientist and author Jared Diamond wrote in a 1995 Discover magazine article that male and female cancer patients being treated with estrogen started to lactate when injected with prolactin (a hormone known to stimulate breast development and milk production in women). Studies have also shown male lactation can also occur when tranquilizers disrupt the function of the hypothalamus — a region of the brain that controls the pituitary gland, the source of prolactin. [5 Myths About the Male Body]
Despite locker-room talk, a 1996 study in the Journal of Urology found that you can’t predict the length of an erect penis by looking at the flaccid version. Some get larger when erect, otherwise known as "growers," while others stay about the same length, sometimes known as "show-ers." However, a stretched penis is a good predictor of its length when erect, according to a 2000 study published in the International Journal of Impotence Research.
A man's prostate gland is perhaps best known for its role in reproduction — it releases fluids that both help sperm swim and protect them once they leave the penis. But it is also sometimes known as the male G-spot. Surrounding the neck of the bladder and urethra, this walnut-size gland can be felt, and stimulated, through the anal canal. The question and answer resource Go Ask Alice! at Columbia University in New York says that men can experience orgasms through prostrate stimulation alone, or in conjunction with other means. [10 Odd Facts About the Female Body]
Men's bodies stink. Reason? Compared with women, guys have more of the hormone androstenone in their sweat and urine. The hormone acts like a pheromone by mammals like boars to signal sexual and social information to other animals. Though humans can smell androstenone, it's unclear whether it plays a similar role for humans. Depending on your genes, however, androstenone can smell like either urine, or vanilla, according to a 2007 study in the journal Nature. Some people can't smell it all.
There are varying levels of gum disease, according to the National Institutes of Health, ranging from gingivitis to chronic periodontitis. And they can affect more than just your mouth. The American Academy of Periodontology states that the inflammation from gum disease has been linked to heart disease, diabetes and rheumatoid arthritis. Other studies have found a potential connection between chronic gum disease and erectile dysfunction. And although there isn't a clear cause-and-effect relationship between the two, a nationwide study in Taiwan found that men with erectile dysfunction were more likely to have been diagnosed with chronic periodontitis than a randomly selected control group. [7 Surprising Reasons for Erectile Dysfunction]