---
title: "List of common misconceptions about science, technology, and mathematics"
chunk: 9/16
source: "https://en.wikipedia.org/wiki/List_of_common_misconceptions_about_science,_technology,_and_mathematics"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:28:18.528573+00:00"
instance: "kb-cron"
---

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"), which are therefore not dependable signs of trouble; indeed, most drowning victims undergoing the response do not show prior evidence of 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.
Sudden immersion into freezing water does not typically cause death by hypothermia, but rather from the cold shock response, which can cause cardiac arrest, heart attack, or hyperventilation leading to drowning.
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.
37 °C (98.6 °F) 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 36.4 °C (97.5 °F), 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 ===