. • It is not just
heavy metals which can be toxic; other metals (for example
beryllium and
lithium) can be toxic too. • Sleeping in a closed room with an electric fan running does not result in "
fan death", as is widely believed in South Korea among older people. As of 2019, this belief was in decline. •
Nocturia (waking up at night to urinate) is equally prevalent in women and men, although it is more common among both men and women over 50. •
Waking up a sleepwalker does not harm them. Sleepwalkers may be confused or disoriented for a short time after awakening, but the health risks associated with sleepwalking are from injury or insomnia, not from being awakened. •
Seizures cannot cause a person to swallow their own tongue, and it is dangerous to attempt to place a foreign object into a convulsing person's mouth. Instead it is recommended to gently lay a convulsing person on their side to minimize the risk of asphyxiation. •
Drowning is often inconspicuous to onlookers. In most cases, the
instinctive drowning response prevents the victim from waving or yelling (known as "aquatic distress"), •
Herbal medicines are not necessarily safe and side-effect free; such medicines can have
adverse effects. • Human blood in
veins is not actually blue. Blood is red due to the presence of
hemoglobin; deoxygenated blood (in veins) has a deep red color, and oxygenated blood (in
arteries) has a light cherry-red color. Veins below the skin can appear blue or green due to
subsurface scattering of light through the skin, and aspects of human color perception. Many medical diagrams also use blue to show veins, and red to show arteries, which contributes to this misconception. • Exposure to a vacuum, or experiencing all but the most extreme
uncontrolled decompression, does not cause the body to explode or internal fluids to boil (although the fluids in the mouth and lungs will indeed boil at altitudes above the
Armstrong limit); rather, it will lead to a loss of
consciousness once the body has depleted the supply of oxygen in the blood, followed by death from
hypoxia within minutes. • Exercise-induced
delayed onset muscle soreness is not caused by
lactic acid build-up. Muscular lactic acid levels return to normal levels within an hour after exercise; delayed onset muscle soreness is thought to be due to
microtrauma from unaccustomed or strenuous exercise. • Stretching before or after exercise does not reduce
delayed onset muscle soreness. •
Urine is not sterile, not even in the bladder. This misconception may derive from urine bacterial screening tests, which return "negative" when bacteria levels are low, but nonzero. •
Cremated remains are not ashes in the usual sense. After the incineration is completed, the dry bone fragments are swept out of the retort and pulverized by a machine called a
cremulator (essentially a high-capacity, high-speed blender) to process them into "ashes" or "cremated remains". • The lung's
alveoli are not tiny balloons that expand and contract under positive pressure following the
Young–Laplace equation, as is taught in some physiology and medical textbooks. The tissue structure is more like a sponge with polygonal spaces that unfold and fold under negative pressure from the chest wall. • Half of
body heat is not lost through the head, and covering the head is no more effective at preventing
heat loss than covering any other portion of the body. Heat is lost from the body in proportion to the amount of exposed skin. The head accounts for around 7–9% of the body's surface, and studies have shown that having one's head submerged in cold water causes a person to lose only 10% more heat overall. •
Adrenochrome is not harvested from living people and has no use as a recreational drug.
Hunter S. Thompson conceived a fictional drug of the same name in his book
Fear and Loathing in Las Vegas, apparently as a metaphor and unaware that a real substance by that name existed; it is Thompson's fictional adrenochrome, and not the real chemical compound, that is the source of numerous conspiracy theories revolving around human trafficking to harvest the fictional drug. • Men and women have the same number of ribs: 24, or 12 pairs. The erroneous idea that women have one more rib than men may stem from the
biblical creation story of
Adam and Eve. • The use of
cotton swabs (a.k.a. cotton buds or Q-Tips) in the ear canal has no associated medical benefits and poses definite medical risks. • The idea that a precise number of stages of grief exists is not supported in peer-reviewed research or objective clinical observation, let alone the
five stages of grief model. • is not the normal or average
temperature of the human body. That figure comes from an 1860 study, but modern research shows that the average internal temperature is , with small fluctuations. • The
cells in the human body are not outnumbered 10 to 1 by
microorganisms. The 10 to 1 ratio was an estimate made in 1972; current estimates put the ratio at either 3 to 1 or 1.3 to 1. • The total length of capillaries in the human body is not 100,000 km. That figure comes from a 1929 book by August Krogh, who used an unrealistically large model person and an inaccurately high density of capillaries. The true number is believed to be between 9,000 and 19,000 km. • Wood smoke, for example from
wood-burning stoves, is not a benign form of pollution because it is "natural", but is as harmful as other common forms of air pollution such as
diesel fumes.
Disease and preventive healthcare • It is not true that more people have died from the
COVID-19 vaccine than from COVID-19 itself. Severe adverse reactions from the vaccine are rare, and an "exceedingly small" number of deaths have been caused by the vaccine. Meanwhile, the death toll from the disease itself is in the millions. •
Tuberculosis is not purely a disease of the lungs that has symptoms of coughing. It may instead infect a wide range of other organs in the body. • Cancer cannot be treated by restricting food intake and so supposedly "starving" tumors. Rather, the health of people with cancer is best served by maintaining a
healthy diet. • The
common cold and the
common flu are caused by
viruses, not exposure to cold temperatures. However, low temperatures may somewhat weaken the immune system, and someone already infected with a cold or influenza virus but showing no symptoms can become symptomatic after they are exposed to low temperatures. Viruses are more likely to spread during the winter for a variety of reasons such as dry air, less air circulation in homes, people spending more time indoors, and lower
vitamin D levels in humans. •
Antibiotics will not cure a cold; they treat bacterial diseases and are ineffectual against viruses. However, they are sometimes prescribed to prevent or treat
secondary infections. • There is little to no evidence that any illnesses are curable through
essential oils or
aromatherapy, and
fish oil has not been shown to cure
dementia. • In those with the common cold, the color of the
sputum or nasal secretion may vary from colorless to yellow to green and does not indicate the class of agent causing the infection. The color of the sputum is determined by
immune cells fighting an infection in the nasal area. •
Vitamin C does not prevent or treat the common cold, although it may have a protective effect during intense cold-weather exercise. If taken daily, it may slightly reduce the duration and severity of colds, but it has no effect if taken after the cold starts. • Supplements of the plant
echinacea do not prevent or reduce the severity of colds as widely believed. A 2014 review of 24 different randomized controlled trials found echinacea supplements do not prevent colds, with most showing no benefit over placebo. • s and cannot cause warts on humans. Humans cannot catch warts from toads or other animals; the bumps on a toad are not warts.
Warts on human skin are caused by
human papillomavirus, which is known to affect only humans. •
Cracking one's knuckles does not cause
osteoarthritis. • In people with
eczema, bathing does not dry the skin as long as a moisturizer is applied soon after. If moisturizer is not applied after bathing, then the evaporation of water from the skin can result in dryness. • There have never been any programs in the US that provide access to
dialysis machines in exchange for pull tabs on beverage cans. This rumor has existed since at least the 1970s, and usually cites the
National Kidney Foundation as the organization offering the program. The Foundation itself has denied the rumor, noting that dialysis machines are primarily funded by Medicare. •
Rhinoceros horn in powdered form is not used as an
aphrodisiac in
traditional Chinese medicine as
Cornu Rhinoceri Asiatici (犀角,
xījiǎo, "rhinoceros horn"). It is prescribed for fevers and convulsions, a treatment not supported by
evidence-based medicine. •
Leprosy is not auto-degenerative as commonly supposed, meaning that it will not (on its own) cause body parts to be damaged or fall off. Leprosy causes rashes to form and may degrade cartilage and, if untreated,
inflame tissue. In addition, leprosy is only mildly contagious, partly because 95% of those infected with the mycobacteria that cause leprosy do not develop the disease. •
Rust itself does not cause
tetanus infection. The
bacterium that causes tetanus thrives in
low oxygen environments, including rust where the oxygen has combined with iron, so many people associate rust with tetanus. However, any puncture wound can introduce spores that cause a tetanus infection, not just rusty nails. •
Quarantine has never been a standard procedure for those with
severe combined immunodeficiency, despite the condition's popular nickname ("bubble boy syndrome") and its portrayal in films. A
bone marrow transplant in the earliest months of life is the standard course of treatment. The exceptional case of
David Vetter, who lived much of his life encased in a sterile environment because he would not receive a transplant until age 12, was an inspiration for the "bubble boy" trope. •
Post-exposure prophylaxis for
rabies does not require a painful series of injections into the abdomen with a long needle. Prior to the 1980s, the rabies vaccine did indeed require injection into the abdomen, but modern rabies vaccines are given as
intramuscular injections into the
deltoid muscle of the upper arm. • Statements in
medication package inserts listing the frequency of
side effects describe how often the effect occurs after taking a drug, but are not making any assertion that there is a causal connection between taking the drug and the occurrence of the side effect. In other words, what is being reported on is correlation, not necessarily causation. • There is no peer-reviewed scientific evidence that
crystal healing has any effect beyond acting as a placebo. • There is a scientific consensus that currently available food derived from
genetically modified crops poses no greater risk to human health than conventional food. • Reading in dim light causes
eye strain rather than permanent damage to the eye. • A
fever from infection does not cause brain damage by itself. The myth has been linked to the association between fevers and typically non-serious
febrile seizures. •
Tourette's syndrome is not predominantly characterised by the compulsive or frequent use of profanity or taboo words and phrases (
coprolalia), as it is commonly misunderstood to be. Only approximately 10% of people with Tourette's exhibit coprolalia at all, and most Tourette's tics (which can be physical or verbal) often go unnoticed by casual observers. • The
Hippocratic Oath does not begin, "First do no harm" (
Primum non nocere), nor is the word "First" present in the original text. Physicians taking the Hippocratic Oath vow, however, to "abstain from all intentional wrong-doing and harm".
Nutrition, food, and drink •
Diet has little influence on the body's
detoxification, and there is no evidence that
detoxification diets rid the body of toxins. Toxins are metabolized and removed from the bloodstream by the liver and kidneys, and they are primarily removed from the body in urine and bile (excreted with the feces). As a result, they do not need to be avoided by those with the flu or cold
congestion. However, milk and saliva in one's mouth mix to create a thick liquid that can briefly coat the mouth and throat. The sensation that lingers may be mistaken for increased
phlegm. •
Drinking eight glasses (2–3 liters) of water a day is not needed to maintain health. The amount of water needed varies by person, weight, diet, activity level, clothing, and the ambient temperature and humidity. Water requirements can be met from liquids such as juices, tea, milk, soups, etc., and from foods including fruits and vegetables. • Drinking coffee and other caffeinated beverages does not cause dehydration for regular drinkers, although it can for occasional drinkers. • Neither spicy food nor coffee has a significant effect on the development of
peptic ulcers. • Sugar does not cause
clinical hyperactivity in children. Double-blind trials have shown no difference in behavior between children given sugar-full or sugar-free diets, even in studies specifically looking at children with
attention deficit hyperactivity disorder or those considered sensitive to sugar. A 2019 meta-analysis found no positive effect of sugar consumption on
mood but did find an association with lower alertness and increased fatigue within an hour of consumption, known as a
sugar crash. Sugar can, however, lead to a jump in blood sugar levels, causing temporary hyperactivity even if it does not cause clinical hyperactivity. • Eating nuts, popcorn, or seeds does not increase the risk of
diverticulitis. These foods may actually have a protective effect. • Eating less than an hour before swimming does not significantly increase the risk of experiencing muscle cramps, and does not increase the risk of drowning. One study shows a correlation between alcohol consumption and drowning, but not between eating and stomach cramps. •
Vegan and
vegetarian diets can provide enough protein for adequate nutrition. In fact, typical protein intakes of
ovo-lacto vegetarians meet or exceed requirements. The American Dietetic Association maintains that appropriately planned vegetarian diets are healthful. However, a vegan diet does require
dietary supplements. •
Swallowed chewing gum does not take seven years to digest. Chewing gum is mostly indigestible, and passes through the digestive system at the same rate as other matter. • The
beta carotene in carrots does not enhance
night vision beyond normal levels for people receiving an adequate amount, only in those with a
deficiency of vitamin A. •
Spinach is not a particularly good source of
dietary iron. While it does contain more iron than many vegetables such as asparagus, Swiss chard, kale, or arugula, it contains only about one-third to one-fifth of the iron in lima beans, chickpeas, apricots, or wheat germ. Additionally, the
non-heme iron found in spinach and other vegetables is not as readily absorbed as the
heme iron found in meats and fish. • Most cases of
obesity are not related to slower
resting metabolism. Resting metabolic rate does not vary much between people. Overweight people tend to underestimate the amount of food they eat, and underweight people tend to overestimate. In fact, overweight people tend to have faster metabolic rates due to the increased energy required by the larger body. • Eating normal amounts of soy does not cause
hormonal imbalance. • There is no good evidence that
low-carbohydrate diets have any health benefits besides
weight loss, for which they are about as effective as other diets. Weight loss is primarily a result of
caloric restriction, and is not significantly influenced by the balance between fat and carbohydrate in one's diet.
Alcohol •
Alcoholic beverages do not make the entire body warmer. Alcoholic drinks create the sensation of warmth because they cause blood vessels to dilate and stimulate nerve endings near the surface of the skin with an influx of warm blood. This can actually result in making the core body temperature lower, as it allows for easier heat exchange with a cold external environment. • Alcohol does not necessarily kill brain cells. Alcohol can, however, lead
indirectly to the death of brain cells in two ways. First, in chronic, heavy alcohol users whose brains have adapted to the effects of alcohol, abrupt ceasing following heavy use can cause
excitotoxicity leading to cellular death in multiple areas of the brain. Second, in alcoholics who get most of their daily calories from alcohol, a deficiency of
thiamine can produce
Korsakoff's syndrome, which is associated with serious brain damage. • The order in which different types of alcoholic beverages are consumed ("Grape or grain but never the twain" and "Beer before liquor never sicker; liquor before beer in the clear") does not affect
hangover severity. • Authentic
absinthe has no
hallucinogenic properties, and is no more dangerous than any other alcoholic beverage of equivalent proof. This misconception stems from late-19th- and early-20th-century distillers who produced cheap knockoff versions of absinthe, which used
copper salts to recreate the distinct green color of true absinthe, and some also reportedly adulterated cheap absinthe with poisonous
antimony trichloride, reputed to enhance the
louche effect.
Sexuality and reproduction •
Older adults are not necessarily sexually inactive nor have they lost interest in sex; although the frequency of sexual activity tends to decline with age. One survey in
England of people aged 60–69 recorded 86% of men and 60% of women as sexually active. • It is not possible to get pregnant from semen released in a commercial
swimming pool without
penetration. The sperm cells would be quickly killed by the
chlorinated water and would not survive long enough to reach the vagina. • An examination of the
hymen is not an accurate or reliable indicator that a woman or girl has had penetrative
sex, because the tearing of the hymen may have been the result of some other event, and some women are born without one.
Virginity tests, such as the
"two-finger" test, are unscientific. • Hand size and foot size do not correlate with
human penis size, but
finger length ratio may. • While pregnancies from sex between
first cousins do carry a slightly elevated risk of
birth defects, this risk is often exaggerated. The risk is 5–6% (similar to that of a woman in her early 40s giving birth), compared with a baseline risk of 3–4%. • Having sex before a sporting event or contest is not physiologically detrimental to performance. In fact some studies suggest that sex prior to sports activity can elevate male
testosterone levels (which could potentially enhance performance for male athletes), while long periods of abstinence can reduce those levels. • The heightened sensitivity some women experience at the
G-spot is not due to it being a distinct anatomical structure, but rather because pressure in that area may stimulate other internal structures, notably the
Skene's gland. Many
sexologists take issue with the term, concerned that women who "fail to find their G-spot" may feel abnormal. •
Closeted or
latent homosexuality is not correlated with
internalized homophobia. A 1996 study claiming a connection in men has not been verified by subsequent studies, including a 2013 study that found no correlation. • The
menstrual cycles of women who live together do not
tend to synchronize. A 1971 study made this claim, but subsequent research has not supported it. • Having an
abortion does not increase someone's
risk of developing breast cancer. Some smaller, less reliable early studies suggested that abortion could be linked to breast cancer, but the scientific community has concluded that abortion does not cause breast cancer. • There is no evidence that English-speaking
Christian missionaries encouraged
converts to use the
missionary position in the
colonial era. This notion probably originated from
Alfred Kinsey's
Sexual Behavior in the Human Male (1948) through misunderstandings and misinterpretations of historical documents.
Skin and hair •
Water-induced wrinkles are not caused by the skin absorbing water and swelling. They are caused by the
autonomic nervous system, which triggers localized
vasoconstriction in response to wet skin, yielding a wrinkled appearance. • A person's hair and fingernails do not continue to
grow after death. Rather, the skin dries and shrinks away from the bases of hairs and nails, giving the appearance of growth. • Shaving does not cause
terminal hair to grow back thicker or darker. This belief is thought to be due to the fact that hair that has never been cut has a tapered end, so after cutting, the base of the hair is blunt and appears thicker and feels coarser. The fact that short hairs are less flexible than longer hairs contributes to this effect. •
MC1R, the gene mostly responsible for red hair, is not
becoming extinct, nor will the
gene for blond hair do so, although both are
recessive alleles. Redheads and blonds may become rarer but will not die out unless everyone who carries those alleles dies without passing their hair color genes on to their children. •
Acne is not caused by a lack of hygiene or eating fatty foods, though certain medications or a
carbohydrate-rich diet may worsen it. •
Dandruff is not caused by poor hygiene, though infrequent hair-washing can make it more obvious. The exact causes of dandruff are uncertain, but they are believed to be mostly genetic and environmental factors. == Inventions ==