Things you had no idea are contagious -

When something is contagious, it means it’s transmissible and it can spread from one person to another. We often associate this with diseases, but many other things can be—and indeed are—contagious. We’re talking about sensations, emotional states, behaviors, and actions.

In this gallery, we bring you a number of things you may not know are contagious. Click on to discover them.

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Feeling cold -

Temperature contagion is a thing. Research conducted at the University of Sussex in the UK found that just looking at someone who is cold will make our own body temperature drop.

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Feeling cold -

The study had participants watching a video of a person plunging their hand into ice water. The viewers not only reported feeling cold, but the actual temperature of their hands decreased!

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Feeling cold -

Interestingly, temperature contagion was not observed when participants were exposed to a similar video, but in a warm setting. "We think that this is probably because the warm videos were less potent—the only cues that the water was warm was steam at the beginning of the videos and the pink color of the actor's hand (whereas blocks of ice were clearly visible throughout the duration of the cold video). There is also some evidence to suggest that people may be more sensitive to others appearing cold than hot."

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Loneliness -

A large-scale study, which considered data for more than 60 years, found that lonely people often share their loneliness with other people. These people, in turn, start to feel lonely as well.

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Loneliness -

"We detected an extraordinary pattern of contagion that leads people to be moved to the edge of the social network when they become lonely," said the leader of the study, University of Chicago psychologist John Cacioppo.

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Laughter -

Laughing is definitely contagious. According to psychologist Robert Provine, “you're 30 times more likely to laugh with other people than you are on your own.”

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Yawning -

Raise your hand if you yawn when you see someone else doing it! This behavior can even occur when we hear, or even read, about someone yawning. Some research justifies the phenomenon as a synchronized group behavior.

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Noncommunicable diseases -

Noncommunicable diseases (NCDs) are conditions that are usually not caused by an acute infection and that can't be transmitted between people. NCDs are believed to be caused by a mix of genetics, environmental factors, and lifestyle choices. Examples include heart disease, diabetes, cancer, and obesity.

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Noncommunicable diseases -

A 2020 paper by the Canadian Institute for Advanced Research (CIFAR) suggests that NCDs may actually be transmittable. The research looked at how people who suffer from these conditions had one thing in common: altered microbiomes (microorganisms such as bacteria, fungi, and viruses).

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Noncommunicable diseases -

The scientists discovered that transplanting the altered microbiomes into animals caused the disease. As a result, the study proposed that "some NCDs could have a microbial component and, if so, might be communicable via the microbiota.” This research, however, is not conclusive.

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Restaurant orders -

A study conducted by the University of Illinois found that diners tend to order foods that are similar to those of their companions. “Diners wanted to be different from their dining companions, but not too different,” explained researcher Brenna Ellison.

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Divorce -

A 2013 study found that people who were friends with divorcees were 75% more likely to get a divorce than those whose friends were still married.

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Goals -

Another person's behavior, especially in our inner circles, can affect ours. How many times has someone left a party early and you found yourself looking at the watch, too? The same applies with goals. Let’s take a look at some examples.

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Goals: quit smoking -

A study found that when one person quit smoking, those who were in that person’s inner circle (family and close friends) became 36% less likely to smoke.

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Goals: weight loss -

The ripple effect is also observed in those trying to lose weight. A 2018 study found that “weight loss can spread within couples, and that widely available lifestyle programs have weight loss effects beyond the treated individual.”

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Happiness -

Many of us have experienced this when we are around positive, upbeat people, right? It turns out, this positive influence spreads even further around us. “Even people we don’t know and have never met have [a] bigger effect on our mood than substantial increases in income,” explained James Fowler, a political scientist at the University of California, San Diego, who led a study on happiness.

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Happiness -

The study in question found that those with a positive sibling living nearby may be happier by 14%. A happy next-door neighbor will boost odds of happiness by 34%, while a happy friend living nearby can increase the odds by more than 40%.

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Cancer -

Cancer is a noncommunicable disease, but there are animals that can actually spread cancer to each other, namely Tasmanian devils, soft-shelled clams, and dogs. While the transmission of cancerous cells between humans is not believed to occur under the same circumstances, there are cases where this is believed to have occurred.

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Cancer -

In 2018, an organ donor died of breast cancer, and all four people who received transplants from that person developed breast cancer. But these were patients with already compromised immune systems.

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Itching -

It’s safe to say that most of us have felt our own skin tingling after we’ve seen someone scratch an itch. This happens all the time, and it’s not only limited to humans. Experiments with rats have reached similar conclusions.

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Bad behavior -

A theory known as the broken windows theory suggests that signs of crime, anti-social behavior, and civil disorder trigger more of the same behavior, thus spreading it.

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Bad behavior -

A number of field experiments in the Netherlands suggest that this is indeed the case. The researchers found that “when people observe that others violated a certain social norm or legitimate rule, they are more likely to violate other norms or rules, which causes disorder to spread.”

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High blood pressure -

Researchers found that mice infected with cytomegalovirus (CMV) developed higher blood pressure than those without the virus. CMV altered their behavior and caused them to eat more high-cholesterol foods. And, it turns out, trials with human cell cultures had similar results.

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High blood pressure -

CMV-infected human cell cultures developed a protein that actually contributes to high blood pressure. CMV is transmitted through bodily fluids, and a large chunk of the human population around the world has it.

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Desire for new things -

We tend to rate objects as more valuable when other people want them. Though the “wedding-band syndrome,” as psychologist Elizabeth Lombardo calls it, is also applicable to people. “A man is more attractive if someone already wants him—he must be worth having,” she explained.

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Stomach ulcers -

Stomach ulcers are mainly caused by a bacterium called Helicobacter pylori, which is carried by a large percentage of the world’s population. While many people don’t experience any symptoms, others may develop peptic ulcers in the stomach and small intestine.

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Stomach ulcers -

It turns out this bacterium is transmittable through saliva and fecal matter. So while a stressful lifestyle and spicy foods are sometimes blamed for ulcers, washing your hands will be a more effective way to prevent H. pylori from getting into your body.

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Stress -

When we detect signs of stress in other people, our bodies release stress hormones. And this doesn’t even need to occur in person. This stress response can be triggered by an email, a text, or social media, for example.

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Negative thinking -

According to a study by the University of Notre Dame, you can “catch” negative thinking if exposed to it. The study randomly paired freshmen with roommates who were highly prone to brooding. The freshmen “caught” their negative-thinking style after three months.

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Cavities -

Kissing someone with poor dental hygiene may not be good for your oral health. This is because cavity-causing bacteria may end up in your mouth.

Sources: (The Healthy) (Listverse) (University of Chicago) (Medical News Today) (ScienceDaily) (New Scientist) (American Psychological Association) (NPR)

See also: The most common doubts about oral hygiene (and their answers)

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