Why Does Scratching Make Itching Worse?

iStock/champja
iStock/champja

It feels like a biological blooper: A persistent itch is made worse by scratching, the one thing that provides instantaneous relief. Evolutionary biologists have proposed that the relationship between scratching and itching developed when disease-carrying parasites and insects bit humans, causing itching skin; scratching brushed the bugs away. Anyone suffering from a mosquito bite can understand that connection.

There’s no simple answer for why skin that has just been scratched becomes even itchier, but researchers have identified some mechanisms behind the irritating phenomenon.

Why Scratching an Itch Doesn't Help

Our sensory neurons are constantly bombarded with stimuli, so some sensations take precedence over others. Sensory signals of one type can be overridden by signals of other types if the latter are strong enough. The overridden signals don’t even reach the brain—they’re stopped by specific neurons in the spinal cord. In this way, the pain caused by scratching is often sufficient to drown out the itch—but only temporarily.

Cells in the brain stem produce the neurotransmitter serotonin, which quells pain. But according to Zhou-Feng Chen, Ph.D., director of the Center for the Study of Itch at Washington University School of Medicine in St. Louis, Missouri, serotonin has an additional function. His group has found that as the serotonin spreads through the spinal cord, it can activate neurons that transmit itch signals to the brain, compelling us to scratch even more.

Each time we scratch, we put this cycle in motion. The increasing amount of serotonin may even make us scratch harder, until the urge to scratch becomes detached from any itch trigger on the skin. “It’s to try to suppress the itchy sensation, which occurs in your brain,” Chen tells Mental Floss. By this mechanism, itches can even become chronic.

Serotonin signaling isn’t the only way scratching worsens an itch; harm to the skin caused by scratching is another contributor. “When the skin barrier is irritated or further damaged, it releases certain pro-inflammatory factors that can directly aggravate itch by stimulating the sensory nerve fibers,” Brian Kim, M.D., co-director of the Center for the Study of Itch, tells Mental Floss. Those factors can also activate your immune system, and some types of immune cells around the affected area may produce chemicals that induce itch.

The very idea of scratching can also be a trigger. Chen’s research group reported last year that mice appear susceptible to scratching when they see other mice do the same. “Itching is actually contagious between people, between animals, and in your body itself,” Chen says. “When you scratch one place, you quickly want to scratch another area.” Scratching doesn’t just make itch more intense—it sometimes also causes the sensation to spread.

Relief for Itching

In mild cases, it may be possible to resist scratching through sheer force of will—but that’s not usually a long-term solution.

“I always feel bad because a lot of people say to patients, ‘Don’t scratch, don’t scratch,’ but that’s very challenging,” Kim tells Mental Floss. He says he tries to determine the cause of a person’s itchiness first. If it’s caused by an underlying medical problem, such as infestation with lice or liver disease, managing that issue may resolve the itch. Even if the underlying problem can’t be cured, there are medications that can calm itch in certain circumstances, such as antihistamines for allergy-induced itch and topical corticosteroids for itch caused by certain skin conditions, including eczema.

For now, drugs like these may be our best weapons against itching. “I think itch is often viewed as quirky, not serious, or embarrassing,” Kim says, which explains why there’s little research on itch despite its impact on our lives. Unfortunately, that coveted scratch in a bottle remains out of reach.

9 Surprising Facts About the Scientific Study of Sex

vadimguzhva/iStock via Getty Images
vadimguzhva/iStock via Getty Images

The scientific study of sex is much more exciting than an awkward sex ed class. While writing my book Sex Weird-o-Pedia, these were some of the most interesting facts about science and sex that I came across.

1. Some sex researchers didn't want their findings to get into the wrong hands.

The pioneering sex researcher Richard von Krafft-Ebing didn’t want his knowledge in the hands of ordinary folk. So he wrote Psychopathia Sexualis, the founding document of modern sexology—which was published in Germany in 1886 then translated and published in English in 1939—in Latin to discourage regular Joes (and/or Janes) from reading it.

2. You burn more calories mowing the lawn than you do having sex.

Young woman poses for selfie while mowing the lawn
Alina Rosanova/iStock via Getty Images

Sex might seem strenuous when things get hot and heavy, but it's usually not that great of a workout. You'd have to go at it for nearly 200 minutes to burn as much energy having sex as you do during a 30-minute run. Even mowing the lawn burns about three times more calories than sex. According to the British Heart Foundation, sex burns about the same amount of energy per minute as ironing clothes.

3. A surprising number of mothers claim to be virgins.

In a 2013 study of several thousand pregnant women in the U.S. published by BMJ, about 1 percent of the participants claimed they were virgins when they gave birth. This, of course, calls into question the veracity of studies that rely on self-reported sexual behaviors.

4. Penicillin may have ignited the sexual revolution.

One economist says that penicillin, and not the birth control pill, was the real enabler of the sexual revolution. A study published in the Archives of Sexual Behavior in 2013 shows that penicillin contributed to a 75 percent decline in the number of deaths caused by syphilis from 1947 to 1957. Since the new treatment made sex safer, people started having riskier sex, which resulted in increases in the numbers of children born out of wedlock and teenage pregnancies.

5. Twins can have different dads.

A photo of fraternal twins
Aleksandr Zhurilo/iStock via Getty Images

While it is very rare, it is possible for fraternal twins to have two different fathers. What’s more common is for a rom-com to be based on this scenario.

6. Gender may influence how people handle sexual jealousy.

Research from evolutionary psychologists indicates that people’s gender influences how they react to sexual jealousy. For men, they react more strongly to sexual unfaithfulness than emotional infidelity. For women, it is the reverse. The theory behind these behaviors comes back to evolution: Males who were intolerant toward their wives becoming sexually active with other men were less likely to become an object of derision and more likely to see their own genes pass onto future generations. Women who prevented their husbands from emotionally bonding with other women reduced the chances of the men spending their resources on other women.

7. One of Ivan Pavlov's colleagues created his own (slightly x-rated) conditioning experiment with dogs.

You’re probably aware of Russian researcher Ivan Pavlov and his famous conditioning experiment in which he trained a dog to salivate at the sound of a bell. What you might not know is that one of Pavlov’s American students, W. Horsley Gantt, conditioned dogs to become sexually aroused when they heard specific tones. The experiment, according to Mandy Merck's In Your Face: 9 Sexual Studies, was intended "to study conflicts of the drives between ... experimentally induced anxiety states and sexual excitement."

8. Couples whose first child is a girl are more likely to get divorced.

Parents pay attention to their phones instead of their daughter
grinvalds/iStock via Getty Images

Married couples whose first child is a girl are more likely to get divorced than those whose first child is a boy. Scientists are split as to why this is. One theory is that female embryos are better able to endure maternal stress than male embryos, so pregnant women in unhappy marriages are less likely to have a miscarriage if the child they are bearing is a girl. But once they have a daughter, these couples are more likely to split up since there were already fissures in their relationship prior to the child’s birth.

9. There's a link between pubic hair and STIs.

A downside of pubic grooming is that it might raise STI risk. In a study conducted by a University of Texas scholar, people who regularly shaved their pubic areas contracted STIs about 80 percent more often than those who never shaved down there. One suggestion is that those who regularly shave are more likely to tear their skin, making it easier for viruses to enter the body.

Ross Benes is the author of Sex Weird-o-Pedia: The Ultimate Book of Shocking, Scandalous, and Incredibly Bizarre Sex Facts.

Airplane Water Quality Is Even Worse Than Previously Believed

anyaberkut/iStock via Getty Images
anyaberkut/iStock via Getty Images

While air travel is convenient, there's never any promise it will be particularly clean. Security checkpoint bins and airplane tray tables are notorious for harboring germs. In addition to being careful of what you touch, you need to be cautious about what you drink.

Air travelers have been warned in the past about the questionable water quality of major airlines. Owing to inconsistent water transport issues, storage methods, and lackadaisical monitoring, several studies and investigations—including a 2004 report by the U.S. Environmental Protection Agency (EPA)—have found bacterial contamination and even insect eggs lurking in liquid served to passengers in the form of coffee and tea.

Unfortunately, the problem doesn’t appear to be getting any better. A new study on the quality of airline tap water conducted by the Hunter College NYC Food Policy Center found E. coli, coliform bacteria, and other unpleasantries across 11 commercial and 12 regional carriers.

The study ranked airlines according to water quality tests, and whether airlines were forthcoming in disclosing how they handle water transportation and storage for in-flight plumbing, using a scale of 1 to 5. While some airlines, like Alaska and Allegiant, scored well at 3.3, others (including JetBlue, Spirit, Delta, and United) ranked poorly in terms of delivering healthy, clean water, which is often sourced from local municipalities.

Low scores also indicated a lack of transparency about the airlines' water monitoring process. Moving the water from its source through hoses and tanks can create opportunities for the water to become contaminated.

How can questionable water be served? While the EPA introduced an Aircraft Drinking Water Rule in 2011 that mandated quarterly cleanings of airplane holding tanks and bacteria tests, Condé Nast Traveler reports that the agency does little to enforce it, typically opting not to issue fines to airlines found to be in violation of the terms.

The study’s authors recommend people avoid drinking tap water, coffee, or tea while on airplanes and should instead opt for bottled water. Because the stored water is also used for lavatory sinks, it’s possible you might introduce germs to your hands even after “cleaning” them. Hand sanitizer is recommended.

[h/t Condé Nast Traveler]

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