All You Need to Know About How Contagion Shapes the World

"Your smile is contagious."

19-year-old me was a bit caught off guard. I always knew it was easy for me to make friends – I wasn’t shy. I was friendly!

"It makes people warm up to you, you know," the new guy in my class kept going.

Oh?

That was a whole new idea to my young, naive self. Could emotions really be contagious? Are we influenced by the people around us – their moods, their actions? Does it even shape how we think, how we act, or who we are?

I had never really thought about it before, but as I reflected on it, it started to make sense. The way someone else’s energy, whether positive or negative, could shift your own vibe. How we pick up on the feelings of those we are around, almost without realising it.

And that got me wondering—what else might we be catching from the people in our lives, and how much control do we really have over it?

Contagion is a virus or bacteria that spreads through contact and causes a contagious disease. The disease itself or even the transmission of the disease could be called a contagion.

Contagious diseases are spread through contact - either direct or indirect. Direct contact is when you touch someone who is infected, and indirect contact is when you touch an object that is contaminated or even through actions like being in contact with an infected person’s coughing or sneezing.

Now, chances are, when you think of contagion, you are probably thinking of the movie ‘Contagion’ and, by extension, thinking of the COVID-19 pandemic. In certain cases, a contagious disease could fester into an epidemic or even a pandemic.

An epidemic is when a sudden outbreak of a contagious disease affects a massive number of people in a localised area. It is called an epidemic because the number of people affected is more than what is normally expected.

For example, the ebola virus outbreak in 2014 caused an epidemic in West Africa that killed thousands of people. It majorly spread through contact with contaminated body fluids.

A pandemic, however, is a huge cause for alarm as it is a disease epidemic that has spread across a wide geographic area, spanning nations or even continents.

The 1918 influenza pandemic, also known as the Spanish flu, left the world scrambling as it affected over a third of the world's entire population. Of the 500 million people that were infected, it ended the lives of almost 50 million people. It is one of the deadliest pandemics to ever go on a rampage.

Contagion is not just a biological kind; it can also be social, emotional, or financial. It's anything that spreads. So, just like COVID-19, a contagion for obvious reasons, it also manifested a unique form of social contagion.

As the virus gripped the entire world, it also collectively created a mass hysteria of panic buying of essentials. When people saw others stockpiling essentials, they, too, gave in due to a fear of scarcity. The behaviour of others around them affected their decision-making.

Stark images of the virus’ effects and people in masks made the rounds as much as the empty shelves of various department stores worldwide.

It’s simple, really. Contagion is anything that spreads from one person to another. In the context of contagious diseases, a bacterial or viral infection could spread from one person to another by direct or indirect contact, infecting the other person. This new person can now pass on the infection to someone else, either knowingly or unknowingly. Thus, the disease spreads.

Social contagion works the same way. It's when information spreads from one person to another, and over time, it starts affecting the behaviour of a whole society, triggering a mass response. Basically, you see something, and then you do something. It's as simple as that.

Emotional contagion tells a lot about how humans are intrinsically social animals and how we unconsciously mimic the body language or expressions of those around us. It's the way people around us make us feel. The contagion is how feelings or emotions spread from one person to another.

Explanation of the basic mechanics of contagion

Biological contagion

Let’s start with an example. The common cold – it's something we all know too well, right? It's been around forever, pretty much since humans existed. It's highly contagious, and on average, an adult catches it four times a year.

Imagine this: your coworker shows up at work with a cold, coughing and sneezing all over the place. Within no time, you start hearing other people in the office doing the same. And, of course, it doesn’t take long before you go home with a sore throat and a runny nose.

Why is it so easy to spread? Simple – the cold is airborne, which means just being near someone who's sick can make you catch it, too. It's like a chain reaction!

But it doesn’t stop there. It’s not just the physical germs that spread. The stress of dealing with being sick, the frustration of having to take time off work, and even the tiredness from fighting off the infection can all spread, too. Maybe you notice others around you complaining about feeling run down, and before you know it, the whole office is in a “mood” – and that’s another kind of contagion, right?

The thing is, once one person is sick, it can quickly snowball. In a way, you’re not just passing on germs but also behaviours, emotions, and even attitudes. And that’s what makes contagion so powerful: it can ripple out in unexpected ways, affecting much more than just your physical health.

Social contagion

You're probably familiar with the term "viral" video, right? It's like when a video spreads like wildfire, almost like a virus, and everyone’s talking about it before you know it. Then there are people who can totally influence us – our choices, our opinions, and even what we buy. We even have a word for them now: "influencers."

Social contagion, at its heart, is all about how the behaviour of one person (or a group of people) spreads to others and gets copied.

Take the ALS Ice Bucket Challenge, for example. That thing went GLOBAL! Suddenly, everyone – from celebrities to people you went to high school with – was pouring ice-cold water over themselves and posting videos. It was everywhere.

Economic contagion

Economic or financial contagion is when an economic crisis spreads from one region or market to another. It can affect countries in different parts of the world and, in some cases, even ripple across the global economy. And it's not always just about money – sometimes, the crisis can be entirely different.

The term "contagion" isn’t just about the spread of an infectious disease; it also describes how economic, financial, and social impacts can spread across countries and markets.

It highlights how one event can ripple through global economies, affecting industries, financial risks, international trade, and even corporate practices.

What starts in one place can quickly have a far-reaching impact everywhere.

Large-scale biological outbreaks have had a massive impact on the world. Think about the 1918 influenza pandemic, the 2003 SARS outbreak, the 2014 Ebola epidemic, the 2009 H1N1 flu, the 2015 Zika virus epidemic, and, of course, the recent COVID-19 pandemic.

No matter where you are, a virus can hit you with the same symptoms, effects, and even outcomes. Like wildfire, it can spread across borders, causing entire populations to face the same challenges and consequences.

So much for the impact, but how do we distinguish between contagious diseases? What are the different types of infections? And how do they spread exactly?

Let’s dive in!

Even if a disease is infectious, it does not mean it will infect every person who comes in contact with it. In fact, it may also affect different people differently. Whether or not someone develops symptoms is controlled by their level of immunity - active or passive.

Active immunity is when your body produces the antibodies necessary to fight off the virus or whatever is causing the disease. This could be due to vaccination or a previous infection that causes the person to have this immunity permanently throughout their lives.

Passive immunity is when the antibodies are transferred from one person to another, for example, from a mother to a child through the placenta or through breastfeeding. This kind of immunity usually lasts from a few weeks to a few months.

Types of contagious diseases

Bacterial - Most bacteria are harmless and even helpful, like the gut bacteria that help us digest our food. However, some types of bacteria can cause infections, from mild to even life-threatening diseases. Strep throat, whooping cough and tuberculosis are examples of bacterial infections.

Viral - A virus is like a small piece of genetic code that affects all living organisms on this planet. They use your cells to replicate or make more copies of themselves. This can damage your cells and make you fall sick. This is what a viral infection is.

The most common types of viral infections are respiratory or digestive, but could also affect other parts of your body’s system. Influenza, pneumonia, chickenpox, measles, dengue, HIV, HPV, HSV(Genital Herpes) or Hepatitis B.

Fungal - Fungus is a kind of living thing that is classified separately from plants or animals and includes mushrooms, mould or yeast. Only a tiny number of fungi can cause an infection.

Yeast infection or athlete’s foot can cause infection on your skin, and some fungi, like black mould, can cause breathing problems or sinus infections.

Parasitic - Parasites are living things that feed off of you. Unlike bacteria or viruses, they cannot survive independently and need a living host. The most common type of parasite would be lice or tapeworms.

Now that we have discussed the different types of infections let’s talk about how they spread.

Between humans, diseases can spread through direct skin-to-skin contact, through sexual activity, childbirth or through the air.

With contagious diseases, especially respiratory viruses, there is another factor to consider called fomite transmission. It is when the infected person’s respiratory droplets or secretion contaminates surfaces or objects that create these ‘fomites’, which, when you come in contact with them, can infect you, thus spreading the disease.

Sometimes, infections can also spread through food or drinking water, which majorly causes intestinal infections like E. coli.

Infections can also spread from animals to humans through bites or scratches or even through animal bodily fluids like saliva, blood, urine, vomit or faeces. There are also carriers of germs like mosquitoes, flies or ticks.

Apart from this, eating raw or undercooked meat or eggs could also be a recipe for disaster.

Let’s talk about the 1929 Stock Market Crash, which is one of the most classic examples of financial contagion. It all started in the U.S. with the stock market getting way too inflated, thanks to speculative trading and people investing money they didn’t have. The market was on this crazy upward swing, and everyone thought it would continue. But, of course, things couldn’t stay that way forever.

When the crash finally hit, it triggered massive panic. People started selling off their stocks, trying to avoid losing everything, making things even worse. The drop in stock prices wasn’t just a problem for the U.S. – it quickly spread to other countries. Since the world’s markets were connected back then (and still are now), a financial shock in the U.S. rippled out globally, causing a chain reaction.

The crash led to widespread bank failures, which froze credit, and businesses couldn’t get the loans they needed to survive. Unemployment skyrocketed, and the effects were felt in almost every country, causing the Great Depression. So, it wasn’t just a U.S. issue – it became a global crisis, showing how fast financial contagion can spread when markets are interconnected.

The stock market crash and the following Great Depression were key factors leading up to World War II. The economic crisis created widespread poverty and political instability, which allowed extremist movements to gain power.

In Germany, the Depression helped Hitler and the Nazis rise to power as people looked for someone to fix the economy. Meanwhile, facing economic struggles, Japan became more militaristic, contributing to its expansionist actions.

The economic fallout played a big role in creating the conditions for political instability and aggression that ultimately led to the war.

We live in the age of social media, and it’s so different from traditional media like newspapers or television, where you’re mostly passively consuming information. On social media, though, it’s a whole other ball game.

You come across something you like, whether it's funny or informative, and you share it. Then your friend sees it, reacts, and shares it with someone else. That’s how information spreads—you're not just consuming it, you’re actively contributing to its ‘virality.’

Think about how things have changed over the past 20 years. A 17-year-old in Bombay would have talked in a very different way compared to someone their age in Calcutta, Chennai, New York, or London. But today, it’s like an entire generation, no matter where they are in the world, pretty much speaks the same language. We have all adopted a whole new lingo, the Gen Z way of talking.

Have you heard the saying, "You are the average of the five people you spend the most time with?"

It’s one of those quotes that sounds cliché, but there’s definitely some truth to it. The people around us play a huge role in shaping how we behave – how we talk, what we believe in, and how we present ourselves to the world. Humans are social creatures, so it's natural that we’re influenced by those around us but it also shows just how easily we can be affected by others' behavior.

It’s like when you watch a funny movie by yourself, and it doesn’t hit the same, but in a crowded theater, the movie seems funnier because everyone around you is laughing.

Or how a TikTok dance takes over the internet and suddenly everyone’s doing it?

How a TikTok dance is suddenly so popular it has an entire generation in a chokehold?

But social contagion isn’t always about harmless trends. It’s also tied to much more serious behaviors. Think about how extreme dieting, self-harm, or even suicide can spread when people see others around them going through similar things. Or how panic can spread through a crowd, leading to chaos. When there’s an angry mob, people often join in the violence without thinking twice. And there’s also the phenomenon of a copycat serial killer, where one high-profile case leads to others.

The impact of social contagion can be pretty extreme, don’t you think? It can spread things far and wide, and it doesn’t need any resistance to take hold. The thing about it is that no one is really resisting. There’s no conflict, no pushback.

It’s easy for us to be influenced by those around us. We are more open to it. For better or worse.

Ever noticed how when someone smiles at you, you can’t help but smile back? Or how a child might mimic your actions without you even trying? It’s like we’re wired to pick up on the moods and emotions around us.

In a team, if one person is rude or insensitive, that bad mood can quickly spread to others through both their words and even non-verbal cues. It's not just about words—it’s about the emotional atmosphere created through actions and interactions.

Even the content we consume can affect our mood. A sad song can make us feel down, while a funny movie can lift our spirits.

Back in 2014, Facebook stirred up a lot of controversy when researchers from Facebook and Cornell University ran an experiment. They manipulated the news feed of 700,000 users to see if it would affect their emotions. By adjusting the algorithms, they wanted to understand how positive or negative posts influenced the way people behaved.

The study, focused on emotional contagion via social media, showed something pretty surprising. People who were exposed to more positive content tended to post more positively themselves, while those who saw more negative posts ended up sharing more negative content.

This experiment on user behaviour highlighted how much power social media has over our emotions and, ultimately, our mental well-being.

But it’s not just about our mood—social media can also fuel things like mob mentality. When anger or any strong emotion spreads through posts, it can escalate into a collective rage that leads to real-world consequences.

The recent pandemic has had a profound effect on the world and everybody around us. We all know someone we lost to this deadly virus. COVID-19 was a completely new (novel) virus – no one had ever had it before. It was something none of us were prepared for.

We heard countless theories about how the virus started. We watched it spread from a city in China to pretty much every corner of the globe. The biological contagion took a heavy toll and we saw frontline workers risk their lives every single day to save others. We saw people go into quarantine, and suddenly, face masks became the new normal.

We saw social contagion play out as we witnessed the mass panic as people hoarded essentials. We also saw it cause a financial contagion that didn’t just affect one country or region – it hit the global economy hard, causing massive disruptions everywhere.

We saw the vaccine being developed and the collective sense of joy spreading worldwide when it was finally here. We saw the global economy tremble, shift, and adapt. And we saw work-from-home become the new norm, changing how we work forever.

But it wasn’t just the virus itself that reshaped our world. The pandemic forced us to rethink our values, healthcare approach, and the importance of global cooperation. It sparked conversations on inequality, mental health, and the fragility of our systems.

It showed us how interconnected we are and how what happens in one part of the world can quickly impact the rest. And as we slowly emerge from this, we’re learning how to balance the lessons of the past with a new sense of resilience and awareness.

In the end, the pandemic revealed just how powerful contagion can be, not only in spreading diseases but in shaping the way we live, work, and interact with one another. It’s a reminder that we’re all part of a bigger picture and our actions—whether in health, economy or even emotions—have the power to ripple across the world.

So, now you know how contagion spreads and its repercussions. So, how do we protect ourselves from it? Let’s find out!

How do we prevent the spread of disease?

• Get vaccinated - Vaccines help your immune system create special cells to fight diseases. They can prevent you from getting seriously sick if you're exposed to germs and lower the chances of you spreading those germs to others.

• Safe sex - Using condoms during sex is a great way to protect yourself from sexually transmitted diseases. You can also get tested for common STIs to stay on top of your health.

• Practise good hygiene - Soap and hand sanitiser can kill many germs that make us sick. Washing your hands is an easy way to help prevent illness, especially after touching your face.

When you cough or sneeze, cover your face to keep germs from spreading. Using the inside of your elbow is a great way to catch those germs and keep others from breathing them in.

How do we protect ourselves from social or emotional contagion?

• Practising mindfulness - Practicing mindfulness is all about tuning into your thoughts and feelings. Taking a moment to centre yourself and focus on what's happening around you helps you control how you react to situations.

• Pay attention to your social circle - Curate your social circle. Be mindful about who you spend your time with, and try to surround yourself with people who lift you up and support you.

Choose to connect with people who reflect the values and behaviours you want to embrace instead of those who might influence you toward negative habits or attitudes. This can include the content you consume online, podcasts, books, and anything else that shapes your mindset.

• Be selective about media consumption - Try to limit your exposure to content that can negatively impact your mood or influence your decisions without you even realising it, including social media. Especially social media.

• Educate yourself - The greatest form of empowerment is through education. Try to educate yourself about social psychology and how social influence works. Understanding these concepts can help you spot certain patterns and figure out how to navigate them.

• Practise critical thinking - When you come across new information or trends, take a moment to step back and really think about why it's gaining attention. Ask yourself why it's becoming popular and question whether it's truly worth jumping on the bandwagon.

Even though financial contagion may not be in our hands, it is still important to educate ourselves about the basic principles and try to stay ahead of it as best we can.

Understand the potential risks, how markets are connected, and how one financial shock can ripple across the world. This knowledge can help you make smarter decisions, whether it’s in investing, budgeting, or planning for the future.

Protecting ourselves from all types of contagion—whether biological, social, or emotional—requires awareness, action, and responsibility.

By staying informed, being mindful of our influences, and taking steps to safeguard our health, we can reduce the negative impacts and make more empowered, conscious choices in our lives.