10 Common Myths About the Human Body

The human body is complex, but myths and misconceptions are everywhere. Some so-called “facts” have been repeated so often that they are accepted as truth—even though science has debunked them long ago. Here we reveal 10 of the most widespread myths about the body and what science actually says instead.

1. We Only Use 10% of Our Brain

This myth has been repeated in countless films and books, but it is completely false. Modern brain imaging techniques such as fMRI and PET scans show that the entire brain is active at different times—even during simple tasks like breathing, moving, or thinking¹. Every part of the brain has a specialized function, and even during sleep, large regions remain active. There is no “unused reserve” of brainpower.

2. The Body Needs a Detox to Eliminate Toxins

Claims that we must detoxify our bodies with juice cleanses or special diets have no scientific basis. The body already has a highly effective detoxification system—liver, kidneys, lungs, and skin—that constantly breaks down and removes waste². Unless someone suffers from organ failure, this system works without external products. Studies show commercial detox products lack proven benefits and may even disrupt the body’s balance³.

3. You Must Sweat for Exercise to Count

Sweating regulates body temperature, not calorie burn. Sweat levels vary with temperature, clothing, genetics, and activity type⁴. A brisk walk in cold weather may burn as many calories as yoga in a hot studio, despite differences in sweat. Exercise effectiveness depends on intensity and muscle work—not sweat.

4. You Need to Drink Eight Glasses of Water a Day

The “8 glasses” rule is a misinterpretation. The original 1945 guideline recommended about 2.5 liters of fluid daily—but that includes water from food and other drinks⁵. Fruits, vegetables, milk, juice, and even coffee contribute to hydration. The body regulates fluid needs via thirst and hormones, so there is no universal intake rule⁶.

5. Alcohol Kills Brain Cells

It is a persistent myth that alcohol directly kills neurons. Moderate drinking does not cause neuronal death in healthy people. Chronic heavy alcohol use, however, can lead to structural brain changes, reduced brain mass, and nerve pathway damage⁷. These effects are linked to malnutrition, inflammation, and reduced neuroplasticity—not immediate neuron death⁸.

6. Hair and Nails Grow After Death

This is physiologically impossible. After death, blood flow and cellular activity stop, including growth processes⁹. Instead, skin dries out and retracts, creating the illusion of longer hair and nails.

7. You Burn More Fat if You Exercise on an Empty Stomach

Training before breakfast may increase fat usage during the workout itself, but long-term fat loss is nearly identical compared to fed exercise¹⁰. Fasted workouts can also reduce intensity and duration, limiting overall effectiveness. For some, especially women and those with low blood sugar, it can cause dizziness, fatigue, or hormonal imbalances.

8. Cracking Joints Causes Arthritis

Joint cracking is common and usually harmless. The sound comes from gas bubbles popping in joint fluid, not from damage¹¹. Studies show habitual knuckle cracking does not increase arthritis risk. Unless cracking is painful or accompanied by swelling, it is not a sign of disease.

9. Muscle Turns into Fat When You Stop Training

Muscle and fat are completely different tissues with different cell structures and functions¹². When training stops, muscle mass decreases and energy expenditure drops. If calorie intake stays the same, excess calories are stored as fat. Muscles do not “turn into” fat—they shrink while fat increases, often in the same areas, creating the illusion of transformation.

10. The Heart Stops When You Sneeze

Sneezing causes rapid pressure changes in the chest that temporarily affect heart rhythm—but the heart does not stop¹³. A brief slowing of heart rate (vagal reflex) may occur, but this lasts milliseconds. The heart continues beating throughout the sneeze with no health risk.

Summary

From brain myths to exercise misconceptions, these 10 examples show how widespread—but wrong—common beliefs about the body can be. Scientific evidence clearly disproves them, reminding us to question what we hear and rely on verified medical knowledge instead.

Sources

1. Boyd R, Silk JB. How Humans Evolved. 8th ed. W.W. Norton & Company, 2018.

2. Ernst E. “Detox: nonsense or a real need?” Journal of Human Nutrition and Dietetics, 2012.

3. Klein AV, Kiat H. “Detox diets for toxin elimination and weight management: a critical review of the evidence.” Journal of Human Nutrition and Dietetics, 2015.

4. Cheuvront SN, Kenefick RW. “Dehydration: physiology, assessment, and performance effects.” Comprehensive Physiology, 2014.

5. Valtin H. “‘Drink at least eight glasses of water a day.’ Really? Is there scientific evidence for ‘8×8’?” American Journal of Physiology, 2002.

6. Popkin BM, D’Anci KE, Rosenberg IH. “Water, hydration, and health.” Nutrition Reviews, 2010.

7. Harper C. “The neuropathology of alcohol-related brain damage.” Alcohol and Alcoholism, 2009.

8. Oscar-Berman M, Marinković K. “Alcohol: effects on neurobehavioral functions and the brain.” Neuropsychology Review, 2007.

9. Knight B. Forensic Pathology. Arnold Publishers, 2004.

10. Schoenfeld BJ, Aragon AA, Krieger JW. “Effects of meal timing on weight loss and health.” Journal of the International Society of Sports Nutrition, 2015.

11. Kawchuk GN, et al. “Real-time visualization of joint cavitation.” PLoS One, 2015.

12. Tesch PA. “Skeletal muscle adaptations consequent to long-term heavy resistance exercise.” Medicine & Science in Sports & Exercise, 1988.

13. D’Alessandro A, et al. “Cardiac modulation during sneeze reflex: autonomic implications.” Journal of Applied Physiology, 2008.