You know it intimately. Every morning, you climb out of bed with it and give it a good, hard look in the mirror. You scrub it down with soap, fill it up with calories, and occasionally walk it around the block for some fresh air. Most of the time, it’s as comfortable as an old pair of jeans. But occasionally, particularly when something goes wrong, you realize just how much you depend on the nearly miraculous abilities of your human body.

Your body is a very odd place. It’s at once mind-bogglingly complex, supremely adaptable, and hopelessly quirky. Often, it amazes. (For example, in the time you’ve spent reading this introduction, your body has created several million new cells to replace those that have just popped off.) Other times, it’s somewhat less impressive. (Just try laughing while drinking a glass of milk.) But whether it’s dazzling or disappointing, the human body ranks as the most remarkable machine you’ll ever operate.

In this book, you’ll learn how your body works, and how you can keep it in tip-top shape. You’ll discover how to spot potential problems, and you’ll learn to love—or at least live with—its charming and not-so-charming oddities. Along the way, you’ll solve a few mysteries. You’ll see why we use the same hardware to talk, eat, and kiss. You’ll meet the millions of uninvited guests that share your body with you. You’ll also learn why at least one study suggests that you’d be better off preparing dinner on a toilet seat rather than on an average kitchen cutting board (Living in a Bacterial World). You’ll face the ravages of aging, confront the challenges of dieting, explore the riddles of diseases like cancer, and learn what happens when you die. (Unfortunately, this book can’t tell you much about what goes down after that.)

We think you’ll enjoy the tour. After all, you’ll be spending a lot of time in your body. Why not get better acquainted?

About This Book

This book provides a practical look at how to get the most out of your body. What makes this book different from the average self-help guide is the fact that it’s grounded in modern-day biology—that means hard-core sciences like biochemistryand genetics.

Of course, there’s no sense burying you in an avalanche of graduate-school theory. (If that’s the experience you want, have a stiff drink, lie down, and hope the feeling goes away. If that doesn’t work, call the nearest center of higher learning and maybe they can talk you out of it.) Instead, this book teaches you just enough biology for you to understand current research and pick up some practical body-boosting tips.

As you’ll discover, a dash of science can explain quite a few of the stranger details of day-to-day life. For example, simple biology can explain why you get goose bumps when you’re cold (Vellus Hair) and how—or if—antibacterial soaps really work (Living in a Bacterial World). In short, the goal of this book is to give you the scientific insight you need to better your body. You won’t, however, pick up enough science to clone dear, departed Uncle Stan.

About the Outline

Your journey into your body wends its way through 11 chapters:

  • Skin: Your Outer Layer (Chapter 1) looks at your miraculous body wrap. You’ll learn how dead skin cells defend your body and litter your house, what causes everything from a mole to a wrinkle, and how antiperspirants tame body odor.

  • Fat (Chapter 2)sizes up one of the least welcome bodyingredients: fat. You’ll learn why you need it, where it hides, and how your body stores it. You’ll also learn to distinguish healthy diets from the body abusers, and find out whether you’re pre-programmed to pack on the pounds.

  • Muscles (Chapter 3)considers your body’s movers and shakers. You’ll learn how muscles work, why you need to tear them up to make them grow, and how weight training can improve the health of your entire body (whether you’re a man or a woman). You’ll even pick up a batch of simple, effective compound exercises you can do at home.

  • Bones (Chapter 4)strips you down to your skeletal framework. You’ll look at the miniature factories that work inside your bones and learn how to preserve your spine with beneficial standing, sitting, and sleeping postures.

  • The Doors of Perception (Chapter 5) shows you how your sense organs—eyes, ears, nose, and tongue—gather information about the outside world. You’ll learn why nearly everyone eventually becomes nearsighted, what to do about ear wax, and how to tell if you’re a “supertaster”.

  • Your Lungs (Chapter 6) sucks you into the world of your respiratory system. You’ll consider unsettling topics that range from snoring to nasal mucus, examine the fine particles that lodge in your lungs, and get practical techniques for deep breathing and voice projection.

  • Your Heart (Chapter 7) introduces you to the pump inside. You’ll experience a virtual heart attack, learn the essential facts about blood pressure, and see how heart-rate monitoring can help you shape the perfect cardio workout.

  • Your Digestive System (Chapter 8) leads you on a tour through the winding passages of your digestive tract—a nearly 30-foot-long canal that travels from tongue to toilet. Along the way, you’ll sort out the probiotics from the prebiotics, make friends with fiber, and learn what your stool tells the world about you.

  • Your Immune System (Chapter 9) takes you to the battleground between your body and its many enemies. You’ll meet the bacteria that colonize your digestive system, greet the viruses that hijack your body, and discover what turns ordinary cells into cancer

  • Sex and Reproduction (Chapter 10) pulls back the curtain on the male and female sexual organs, explaining how they work and what trips them up. You’ll also learn what health class didn’t tell you about fertility, female pleasure, and the male obsession with size.

  • Your Final Exit: Aging and Death (Chapter 11) takes you to the end of your life, and gives you a long, hard look at what it holds. You’ll learn why you age, why you die, and what’s most likely to do you in. Finally, you’ll get a sobering picture of your final moments, complete with a side trip to the bizarre world of a near-death experience.


There’s one organ you won’t explore in these pages—the three pounds of soggy brain matter that run the whole show. To take a closer look at your brain, its extraordinary powers, and its many embarrassing eccentricities, check out the companion title to this book, Your Brain: The Missing Manual.

Separating Truth from Speculation

The science of human biology evolves rapidly, and the insights in this book are based on many of science’s most recent discoveries. However, as with all scientific knowledge, it’s always possible that better, more comprehensive studies will overturn the concepts we use today or change the way we think about them. In fact, it’s a given.

When dealing with scientific research, this book won’t bury you in footnotes. (The basic idea is that footnotes are only as good as the research on which they’re based, and it’s easy to cite a great deal of nonsense written by a great many people.) Instead, this book uses careful wording to distinguish rock-solid truths from tantalizing speculations. When this book says, “some scientists believe,” you’re about to meet a promising new idea that has some heavyweight science behind it, but hasn’t convinced everyone. When this book says, “one study found,” you’re looking at some provocative new evidence that’s on the cutting edge of scientific research.

About the Missing CD

This book is designed to give you a better understanding of how your body works. As you read through the chapters, you’ll find references to books and websites that offer additional info, insights into current research, and more. To find a concise, chapter-by-chapter list of all these books and sites, head to the Missing Manuals home page ( and click the Missing CD link; then scroll down to Your Body: The Missing Manual and click Missing CD.

You can also find updates to this book on the Missing CD page by clicking the “View Errata for this book” link at the top of the page.

You’re invited and encouraged to submit corrections and updates for this book, too, by clicking the “Submit your own Errata” link on the Missing CD page. To keep the book as up-to-date and accurate as possible, each time we print more copies, we’ll include any confirmed corrections you’ve suggested. We’ll also note all the changes to the book on the Missing CD page, so you can mark important corrections in your own copy of the book, if you like.

About Missing

To see the latest Missing Manuals videos, the most recent blog posts by Missing Manuals authors, the most recent community tweets about Missing Manuals, and special offers on Missing Manuals books, go to the Missing Manuals home page (

We’d love to hear your suggestions for new books in the Missing Manual line. There’s a place for that on the website, too.

And while you’re online, you can register this book at (you can go directly to the registration page at Registering means we can send you updates about this book, and you’ll be eligible for special offers, like discounts on future editions of Your Body: The Missing Manual.

You might also want to visit O’Reilly’s feedback page (, where you can get expert answers to questions that come to you while reading this book. You can also write a book review on this page, as well as find groups for folks who share your interest in Your Body: The Missing Manual.

Safari®Books Online

When you see a Safari® Books Online icon on the cover of your favorite technology book, it means the book is available online through the O’Reilly Network Safari Bookshelf.

Safari offers a solution that’s better than e-Books. It’s a virtual library that lets you easily search thousands of top tech books, cut and paste code samples, download chapters, and find quick answers when you need the most accurate, current information. Try it free at

Get Your Body: The Missing Manual now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.