Health superstitions get passed down by parents, repeated by teachers, and occasionally even stated by doctors who learned them decades ago and never had reason to update. What makes most of these myths interesting is not that they are obviously absurd - it is that they are almost always wrong in a specific and instructive way. They contain misapplied, oversimplified biology which is stretched well beyond what the underlying mechanism can actually support. This article picks apart three of the most common body and health myths and replaces them with what is actually happening at a molecular level, which, in every case, turns out to be more interesting than the myth it replaces.
Myth 1 - "Cracking Your Knuckles Causes Arthritis"
This is perhaps the most universally repeated joint myth, usually delivered by a parent wincing at the sound. The claim is that habitually cracking your knuckles damages the joint and leads to arthritis later in life.
The actual mechanism behind the sound is called tribonucleation. Your finger joints are surrounded by synovial fluid, a viscous liquid that lubricates the joint and contains dissolved gases like carbon dioxide. When you stretch the joint capsule by pulling or bending the finger, the pressure inside the joint drops rapidly. This sudden pressure drop causes the dissolved gas to come out of solution, forming a small cavity or bubble within the fluid. That bubble then collapses almost instantly, and the collapse produces the audible crack.
The arthritis claim has actually been tested directly, in one of the more entertaining experiments in medical history. Dr Donald Unger cracked the knuckles on only his left hand, every day, for over 60 years, leaving his right hand uncracked as a control. He found no difference in arthritis between the two hands, which earned him an Ig Nobel Prize in 2009. Larger formal studies have consistently failed to find any statistically significant association between habitual knuckle cracking and the development of osteoarthritis.
Osteoarthritis develops through cartilage degradation - the progressive breakdown of collagen and proteoglycans within joint cartilage, combined with chronic low-grade inflammation accumulating over years. A brief gas bubble collapsing in synovial fluid has no plausible mechanism for triggering either of these processes.
Myth 2 - "Going Out in Cold Weather Without a Coat Will Give You a Cold"
The common cold is caused by a virus, most frequently rhinovirus, and requires actual viral exposure and successful infection of cells in the upper respiratory tract. Ambient temperature alone, in the absence of viral exposure, cannot cause a cold as there is no pathogen, so there is no infection. So in the most literal sense, the myth is false.
However, cold air causes vasoconstriction in the blood vessels of the nasal mucosa, and some research suggests this may reduce the effectiveness of local immune defences, specifically mucociliary clearance, the mechanism by which tiny hair-like cilia sweep mucus and trapped pathogens out of the nasal passages and airway. A 2015 study found that cooling the nasal cavity by just 5°C measurably reduced the innate immune response to rhinovirus in human nasal cells. This suggests that cold exposure may not cause infection directly, but could plausibly make an existing viral exposure more likely to successfully take hold.
The much stronger explanation for why colds cluster so reliably in winter is behavioural rather than biochemical: people spend significantly more time indoors, in closer proximity to each other, during colder months. This dramatically increases opportunities for viral transmission via respiratory droplets and surface contact, meaning that the crowding effect is doing far more work than the temperature itself.
So, this myth is not entirely a myth, but the causal story is closer to the opposite of what most people assume. It is mostly about indoor crowding, with cold air playing a modest supporting role in local immune defence rather than the cold itself directly "giving" you anything.
Myth 3 - "Eating Sugar Makes Children Hyperactive"
Multiple double-blind, placebo-controlled trials have given children either sugar or a sugar-free placebo without either the children or their parents knowing which they received, and then measured subsequent behaviour. These studies have found no consistent difference in hyperactivity between the two groups.
Sugar, (sucrose and glucose), is metabolised through standard glycolytic pathways, generating ATP through cellular respiration in the same way as any other carbohydrate. There is no direct pharmacological mechanism by which sugar would produce stimulant-like hyperactive behaviour, unlike a genuine stimulant such as caffeine, which directly blocks adenosine receptors in the brain.
The most compelling explanation for why the myth persists comes from a well-known study on expectancy bias. Mothers were told their children had been given a large dose of sugar, when in fact all children received a sugar-free placebo. Mothers who believed their child had consumed sugar rated their behaviour as significantly more hyperactive than mothers who were told their child received a placebo despite there being no actual difference in what either group of children consumed. The far more plausible explanation for the real-world association between sugar and hyperactivity is contextual: sugar tends to be consumed at birthday parties, social events, and other unstructured, exciting environments; settings that independently produce excitable behaviour regardless of diet.
This does not mean excessive sugar consumption is harmless as it has well-documented consequences for dental health and metabolic health, but the specific claim that sugar directly causes hyperactive behaviour does not hold up.