This article was first published in The Skeptical Inquirer.
Some old wives’ tales are easy to dismiss. We all know that masturbating won’t really make your palms grow hair and that neither the position of your belly nor your internal temperature can predict the sex of your baby. However, other old wives’ tales are more difficult to dismiss. White spots on our nails being caused by calcium deficiency seems plausible, even though it’s untrue. Some old wives’ tales aren’t old wives’ tales at all, because an old wives’ tale is, by definition, untrue, and some actually are true!
While it’s important to stay skeptical when taking advice from adages with no clear origins, it turns out that some of these old sayings aren’t as silly as they may seem, once you take a look at the science behind them.
You Can’t Swim after Eating: Old Wives’ Tale
If you’ve ever had a lakeside picnic or grabbed lunch at a water park, you’ve probably heard (or more likely been told by a well-meaning parent) not to swim for 1—2 hours after eating. The reasoning behind this warning is that eating causes your body to divert blood away from your muscles, like arms and legs, in favor of your digestive system. The logic follows that swimming in this state will result in cramps, which can increase your risk of drowning. While this idea certainly seems plausible, there is no evidence to support it.
Surely if digestion is diverting an appreciable amount of blood away from the muscles, swimming times would reflect that, right? Well, a 1962 study had subjects swim 100 yards freestyle at various times (0.5, 1, 1.5, 2, 2.5, and 3 hours) after eating and found no significant difference between times. What if we examine the heart itself? A 1961 study looked for changes in electrocardiograms following distension of the stomach, either by a large meal or a balloon and found no changes compared to before eating or ballooning.
Most damningly, according to a literature review conducted by the Red Cross Scientific Advisory Council, there are “no reported cases of eating before swimming causing or contributing to fatal or non-fatal drowning.”
If You Shave Your Hair, It Will Grow Back Faster, Darker, and/or Coarser: Old Wives’ Tale
Fun fact: About two years ago, I shaved my head. Since then, my hair has grown back, and funnily enough, it’s still the same color and texture as it was before. Despite holding the evidence of this myth’s mythical nature on our literal faces, heads, legs, and underarms, the idea that shaved hair will grow back darker, coarser, faster, or just generally “more” is pervasive. Think about it. If our hair grew back longer, darker, or coarser, surely we’d have noticed a general change in its appearance after a lifetime of shaving.
The root of this old wives’ tale lies in, well, hair’s roots. At their tips, hairs are thin and tapered, but closer to the hair follicle they’re thicker. So, when you shave off the part of the hair that’s above the skin, the part that emerges in a couple of days (or hours) is the thicker root, leading to the appearance that the hair has grown back thicker or coarser. However, as the hair grows back out, it will taper off again, leaving it looking the same as it did before you sliced it. If you wax instead of shaving your hair, you may avoid this temporarily thicker-looking phenomenon. Because wax pulls hairs out from their roots, the entire hair needs to regrow, meaning that it’ll be the tapered end that emerges from the skin rather than the thicker root.
The darker appearances of new hairs can also be blamed on photobleaching, or rather the lack thereof. UV rays from the sun can break down the melanin pigments in our hair, just like chemical bleaches do. New hairs have not been exposed to the sun like their elder counterparts and thus may actually be slightly darker. Interestingly, researchers at 23andMe have identified forty-eight genetic markers that may influence hair photobleaching, which may explain why my hair turns blonde in the summer but my dad’s hair remains stubbornly dark.
Never Wake a Sleepwalker: Old Wives’ Truth
Stories about my sleepwalking are some of my favorites to tell at parties. They’re the ultimate way to tell hilarious tales about silly things I’ve done while not being culpable for my actions. On that note, I once got out of bed and went to the living room, ruffled my boyfriend’s hair, and told him to “eat better food” before returning to bed.
Living with me, one of the things he had to learn early was that there actually is some truth to the adage of “never wake a sleepwalker.” No, not because you can send them into shock or trigger a heart attack, but for your safety.
Sleepwalking usually occurs during the third stage of non-REM sleep, when we are most deeply asleep. Researchers can monitor the electrical activity of the brain using electroencephalography, and in 2011 a team of Italian researchers found that both wake-like and sleep-like brain patterns coexist at the same time. They hypothesize that sleep disorders involving unusual behaviors while asleep (also called parasomnias) could be due to an imbalance between these two states.
One such parasomnia is sleep inertia, also known as sleep drunkenness, wherein following forced arousal, the cognitive impairment from sleep can remain for up to tens of minutes. During this period, the individual can be confused, impulsive, and even violent. There are quite a few cases of recently awoken people harming or even killing people around them. It’s important to note that sleep drunkenness can occur anytime someone is woken from a deep sleep, whether they’re sleepwalking or not.
In a legal sense, a person who does a crime while sleepwalking, or when sleep drunk, is not culpable for their actions. The defense is called automatism because the individual is seen as acting as an automaton, not in control of their actions and with no motivation for the crime. You may be surprised to read just how many sleepwalking homicides have occurred, one of the more recent being only thirty-two years ago in Canada.
So, what should you do if not wake a sleepwalker? Take a page from my boyfriend’s book and gently guide them back to bed. But do make sure to tell them about it in the morning, because they probably won’t remember a thing.
Sitting Too Close to the TV Will Make You Go Blind: Old Wives’ Tale
The basis of TV-proximity-based fears seems to be a 1967 recall of color televisions. The increased voltage found in new color televisions caused a radiation output that exceeded what the federal U.S. government deemed to be safe. As many as 112,000 TVs were affected, and the 1968 Radiation Control for Health and Safety Act was created as a result.
Funny enough, despite the large recall and general public worry, the radiation-emitting TV sets only posed a risk to those who spent excessive amounts of time sitting directly below them. If a more normal viewing position was taken (sitting roughly six feet away from the screen with it positioned at eye level), the risk was negligible. Luckily, modern televisions and computers release little, if any, radiation.
In terms of your eye health, despite what you may think when your eyes are red and sore after working all day on your new Skeptical Inquirer article, screens—be they television, computer, or cellular—are not dangerous in the long term. While often given scary names like “computer vision syndrome,” the dry, red, blurry eyes that come accompanied by headaches and neck pain after a lot of screen time are more properly known as eyestrain and are temporary.
Eyestrain results mostly from forcing our eye (ciliary) muscles to contract for hours on end to keep our screens in focus. Like any muscle, our ciliary muscles get tired and need breaks, hence why most eyestrain can be remedied by a good night’s rest. Glare on our screen causes us to squint, further stressing our muscles.
Another important aspect is blinking. Humans normally blink about twenty times per minute, but computer-users can blink as few as seven times per minute. This causes our corneas to dry out and our vision to appear foggy.
Rest assured, however, that no matter how little you blink, how hard you squint, or how close to your face you put your phone, your vision will not be harmed in the long term.
As for the blue light emanating from your iPhone, its effects are limited to disrupting your melatonin production, a hormone that regulates our sleep timing. There’s some good evidence that blue light blocking glasses (or the new night modes available on phones and computers) can help if you’ve been having trouble falling asleep. However, if you’re worried about blue light causing damage to your eyes long term, don’t be.
Feed a Cold, Starve a Fever: Old Wives’ Tale with a Kernel of Truth
When afflicted with an illness, like the common cold, it’s a natural response to lose your appetite. That makes the second half of this saying easy enough to comply with. As for the first part, beyond chicken soup and maybe some Jell-O, eating while ill can be a difficult task. Even drinking is hard enough that patients often need supplemental fluids when sick. But hey, if it works, hand me the soup. I’ll suffer through some unwanted meals if it makes me feel better faster. But will it?
This piece of outdated medical advice seems to come from the idea that eating can raise the bodily temperature, something that could be beneficial if fighting off an infection, but detrimental if one is already nursing a fever. It’s also worth remembering that it was once thought that the common cold could be caught by exposing oneself to cold weather and that heat was a remedy.
While it is true that eating can help raise your body’s temperature, that’s not the part of this aphorism that may be true. There are some theories as to how and why starving yourself when ill may help you fight an infection, but it’s not specific to a fever.
As you likely know, fevers can help your body fight pathogens, both by creating an inhospitably hot environment that will eliminate some infectious agents and by increasing the rate of reactions inside your body that contribute to your immune response. In a similar vein, some researchers believe that anorexia, the medical term for a loss of appetite, is a bodily response to an infection designed to help you heal faster
There are a few theories to support anorexia as a defense mechanism. First, anorexia is extremely widespread, occurring in almost all mammals. Second, behaviorally, a lack of appetite would keep mammals from leaving the safety of their nest/burrow/home to search for food while cognitively and physically impaired, which would also help reduce heat loss due to movement and therefore preserve the fever the body has so carefully created. Third, not eating will reduce the micronutrients like iron available in the blood plasma that pathogens would use for their own purposes, and last, various immune functions, like the activation of macrophages, seems to be increased under starvation conditions
While mice studies cannot be extrapolated to humans, an interesting 1979 experiment infected mice with Listeria monocytogenes and found that those kept from eating had a mortality rate of 40 percent compared to a mortality rate of 90 percent in those who were force-fed.
We’ll need to see some high-quality research on humans before we make any definitive changes to how we treat illnesses regarding diet, but in the meantime, if you’re not feeling hungry while home sick, don’t force yourself to eat. Experts agree that much more important than what you eat when sick is what you drink, so make avoiding dehydration your priority.