During his lunch hour Professor Piet Hoebeke sometimes sits in a chair and contemplates his penis. “What is it doing? How does it feel? These are good ways of focusing and centering yourself. It’s a vital organ and yet we treat it with such casual disdain,” he says. “The penis is extraordinary and we should cherish it.”

“We live in an age of mass anxiety about this organ,” continues Hoebeke, a urologist at Ghent University Hospital in Belgium, who has more than 30 years of experience in this field of medicine. “And I say that about men as well as women. I regularly see mothers and sons in my clinic; the level of misinformation is often astonishing. We live in the age of social media and Internet porn. The mythology has got out of control.”

Perhaps that’s about to change. Last week Me and My Penis, a Channel 4 documentary, delved into the complexities of modern-day masculinity and provided a rare opportunity for a frank conversation about the male body. Now Hoebeke has distilled his impressive bona fides — can a penis expert be said to have “impressive bona fides”? — into Members Club: a User’s Guide to the Penis, a scientifically informative yet entertaining book that addresses a lot of misconceptions about the organ and how to look after it.

Can a penis expert be said to have “impressive bona fides”?

Among other things, Hoebeke discloses that penile pain during an erection could be the result of a calcified scar (Peyronie’s disease), but if it occurs while urinating it might just be the result of dehydration (urine contains a lot of salt). He explains why ejaculating 21 times a month between the ages of 20 to 40 reduces your chance of getting prostate cancer by as much as 20 percent (“it neutralizes the harmful effect of testosterone on the prostate”), why urine leaves the body in a spiral (“think of the ‘gun barrel sequence’ in James Bond films”) and why white bumps that can form on the shaft of a penis are often quite harmless cysts containing sebum. Have you ever felt as though your penis has “fallen asleep” while riding a bicycle? Don’t panic, it’s probably just a pinched nerve — all you need to do is lower your saddle and adjust its angle so that it stops pressing on your pubic bone.

Hoebeke even suggests exercise regimens for your abdomen and provides advice about penile hygiene and sustenance. “Oh yes, penises like to eat well,” he asserts. In fact, the Belgian expert has an answer for just about every delicate issue a man might be concerned about, from priapism (if it lasts longer than 24 hours you will be in big trouble) to the least painful way to deal with a zip entanglement (it will ruin your jeans, but halve your pain). Here are some of the biggest ones:

Size Does Matter

Penises are getting smaller. In the 1940s Alfred Kinsey’s groundbreaking report Sexual Behaviour in the Human Male concluded the average penis length was just over 5.5 inches. In industrialized countries it is now, on average, more than one-third of an inch shorter. This may be due to measuring techniques (Kinsey sent out postcards and invited men to lay it against their penis, mark its length and send it back). But it could be because of environmental pollution caused by discarded plastics.

“There is some evidence that hormone disruptors in the environment have negatively impacted the size of alligator penises in Florida,” Hoebeke says. “But that should be a concern for human males too since we are also susceptible to these factors, which can reduce fertility as well as penis growth.”

There’s No Need to Be Self-Conscious About Yours

In his book Hoebeke declares that since erect gorillas have a 1.5-inch penis and chimps have a 3-inch erection, 95 percent of human males should be very happy: “They have evolved the largest penis of all the primates.” If you stand 100 men in a row and give them an erection then almost all will be 5 inches in length. Let the erection subside and differences will become apparent. This is because of the dartos muscle, which retracts the penis during moments of stress or cold. Some men have an active dartos muscle and some don’t.

If you stand 100 men in a row and give them an erection then almost all will be 5 inches in length.

“That’s why in the chilly changing room some men’s resting penis is almost the same length as when aroused and some men’s shrink by several centimeters,” Hoebeke says.

A 2014 study of more than 15,000 men from around the world showed that the average SPL (stretched penile length, not quite an erection, but the standard measuring mode for penises) was 5.19 inches. The average flaccid length was 3.6 inches. On what Hoebeke calls the world map of penis size, men from sub-Saharan Africa usually have a penis that is longer than the world average. Men from east Asia have averagely shorter ones. But he insists: “The truth is, most men have the perfect penis. It penetrates the vagina, giving pleasure and delivering sperm. So much else is in the mind.”

Penis Enlargement Is Pointless

Hoebeke says that 95 percent of men regret opting for a surgical penis extension and believes the other 5 percent are just lying to themselves because they pay so much for the operation. “You cannot satisfactorily lengthen the penis by surgery,” he says, although he has conducted phalloplasty on people transitioning to become male (where a penis is constructed with a tube created from harvested arm skin). “For me there is a difference between helping patients transitioning gender to those who simply want a cosmetic enhancement.”

Length has long been a cause of male anxiety. But girth can be an issue too. He writes in his book that some Bulgarian men are known to inject their organ with Vaseline to make it appear fatter. Hoebeke used to inject penises with Botox. “It soon felt pointless and wrong so I stopped. The effect lasted for three months and it was cosmetic rather than clinical work.”

Hoebeke says that 95 percent of men regret opting for a surgical penis extension and believes the other 5 percent are just lying to themselves because they pay so much for the operation.

All is not lost. Hoebeke says if you really want to increase the length of your penis, then lose weight to make yours more visible. “You can add one centimeter this way.”

That Problem at the Urinal …

It’s not your fault, Hoebeke says. “Standing to wee at a toilet is a modern convenience, but it can lead to dribbles.” Men are adapted to wee sitting down. As cavemen we would have squatted with our backs to a tree monitoring the surroundings for enemies or predators. Squatting to wee, which is still common in Asia, means your urethra hangs down in a straight line, emptying all urine in the bladder. “An easy remedy is to press the gap between the anus and scrotum which will release residual urine from the bladder,” Hoebeke says, which might make for an awkward conversation the next time you’re in a public toilet.

Premature Ejaculation Is Treatable

In our ancient past, premature ejaculation was probably quite normal and, given the dangers, even advisable. These days the average intravaginal latency time (the period between vaginal penetration and ejaculation) is two to three minutes. Hoebeke has treated men who climax within ten seconds. “There are a number of treatments including circumcision (the exposed penis glans becomes slightly tougher and less sensitive in circumcised men) or simply practicing pelvic floor discipline. But talking about it is often the answer too.”

Yes, You Can Fracture It

It doesn’t have a bone, but the tube of solid tissue surrounding the erectile tissue can tear during sex (you will hear a crunching noise, feel a sharp pain and “it quickly swells up purplish blue and starts to resemble an aubergine” warns Hoebeke in his book). If this occurs, a swift trip to A&E is required. A stitch in time may well prevent a permanent bend.

Care and Maintenance

Hoebeke recommends men follow “penisfulness” — a form of wellness that focuses on the male genitals. “Think about the scrotum and testicles. Ask how they are,” he counsels. I have enough trouble remembering aunts and uncles, so this is a big challenge.

He also has firm ideas on a healthy penis diet. Arginine, an amino acid, strengthens the immune system and the male libido. It also promotes nitrous oxide production essential for erections. Red food is a rich source of arginine: beetroots, peppers, chile, red onions, tomatoes and cranberries. Generally, a vegetarian diet is best for your penis and, perhaps inevitably, so are nuts.

Hoebeke recommends men follow “penisfulness” — a form of wellness that focuses on the male genitals.

“Let’s be clear,” Hoebeke says. “You must still put the food in your mouth, but the penis will be grateful. Think of your penis as the canary in the coal mine. It’s the first thing to drop off its perch when health matters generally are not right.”

The Female Gaze

The penis may have once been the foremost metric of sexual selection, but since humans have started wearing clothes it has slipped down the priority list, Hoebeke says. In modern societies women typically assess potential partners in other ways first.

Arginine, an amino acid, strengthens the immune system and the male libido.

“Eye-gaze analysis shows that women look at shoulders, arms, butt and general muscles long before they consider the trouser bulge,” he says. “It’s not the marketing tool it was once upon a time.”

And men, if a woman looks down at your feet, she’s just judging you on the state of your footwear — there is no correlation between the size of a man’s feet and his penis length. However, there is a weak correlation between height and penis size as well as relative ring- and index-finger length (male hormones secreted before birth are said to dictate this so-called digit-ratio and also the size of the penis; the lower the ratio, the shorter the penis). So pull your shoulders back and take your hands out of your pockets.

Members Club: A User’s Guide to the Penis is published by Green Tree at £14.99 in the U.K. In the U.S., it is available on Kindle and will be published by Green Tree at $20 in November

Michael Odell is a writer for The Times. He is the author of The “Call Yourself British” Quiz Book