Article by Ellen Hendriksen, PhD from Scientific American

“Is depression contagious? The short answer is: yes—it’s not called the common cold of mental illness for nothing.

But like most things, it’s complicated. Depression is contagious, but it’s not as if you get infected when your depressed friend cries on your shoulder. Instead, your own susceptibility or immunity depends on lots of things–your genetics, history, stress, and more.

It’s been known for almost a decade that both healthy and unhealthy behaviors are contagious—if your friends quit smoking or become obese, you’re more likely to do so, too. Even suicide can come in clusters.

Depression comes with its own set of unhealthy behaviors—pessimistic talk, criticizing self and others, cancelling social plans, getting into unhealthy sleeping and eating patterns, and generally being irritable or withdrawn. And it turns out that these behaviors—and the negative beliefs that drive them—can be communicated from person to person.

So roommates of depressed college students, children of depressed parents, and yes, for the listener who requested this episode, spouses of depressed partners also show comparable depressive symptoms.

And it’s not just the people you live with or see every day—emotions can be contagious within up to three degrees of separation. Better hope Kevin Bacon’s not depressed or all of Hollywood is going down.

Let’s look more closely at a study of college roommates that came out in 2014. Researchers studied over 100 pairs of newly assigned freshman roommates at move-in, and then again three and six months later. They examined, among other things, the students’ symptoms of depression and their tendency to ruminate—that is, their inclination to get tangled up in their own lousy feelings and to obsess about the causes and consequences of feeling bad.

Sure enough, freshmen who were paired with a roommate with a tendency to ruminate also picked up the tendency, which greatly increased their risk of depression. To be clear: depression symptoms themselves weren’t contagious, but thinking styles were. Freshmen who “caught” a ruminative style of thinking from their roommates had twice as many depressive symptoms after six months as those who didn’t pick up the thinking style.

Next, a 2015 study showed that depression can be made contagious under laboratory conditions, at least in rats. Researchers induced depression in rats by putting them through unpredictable, uncontrollable stressors over several weeks—a close approximation of chronic stress in people. For the rats, it meant things like keeping the lights on for 48 hours at a stretch and spilling water on their bedding—all probably better than being a pet in a kindergarten classroom, but still enough to make the rats depressed. For a rat, that doesn’t mean turning down invitations to Rats’ Night Out—it means an apathy to sugar water, a lab rat’s greatest pleasure. This is a marker of anhedonia—a hallmark symptom of depression in people and, apparently, rats.

After the rats became depressed, the researchers introduced some new roommates. Two depressed rats and a new, fresh-faced non-depressed rat (“Hiya guys!”) were housed together. Turns out living with someone depressed is, well, depressing, even if you’re a rat. Within just a few weeks, the new rats exhibited the same symptoms as the depressed rats.

Now, we can’t replicate such a controlled experiment with humans (I don’t think I’d let researchers come to my house and spill water on my bedding), but it makes sense. Given enough airtime, a negative outlook—about the world, yourself, and the future—can be convincing. If your depressed roommate or partner is critical, withdrawn, apathetic, and convinces you things will never get better, the dark cloud can spread over you, too.

Now, does this mean you should drop your depressed friend or partner? Unfortunately, only you can answer that one. It’s a tough challenge without an easy solution.

On the one hand, do your best to communicate that your loved one is just that: loved. Not to mention that they are important to you, worthy of your love, and deserving of feeling better. Encourage them to seek help, but it may take an incredible amount of bravery on their part (and patience on yours) to take the first step.

On the other hand, staying out of guilt when you’ve given your all isn’t an option either. You can’t rescue your loved one. You’re up against a host of factors, none of which you can control and there may come a point where you need to save yourself. Depression annihilates any shred of motivation; in severe depression, it can be difficult to get motivated to eat, shower, or unfortunately, seek help or make changes in one’s life.

One hopeful note: it’s not only depressive thinking that’s contagious. Positive emotions and thinking styles can be contagious, too. Think of the rush of excitement at a sports event or concert, the palpable calm after a yoga class, the simple courtesy of service with a smile, and of course, the warm fuzzies from hugging someone you love. Indeed, in the roommate study, freshmen who were paired with a roommate whose thinking style was more positive “caught” a healthier thinking style.

To sum up, emotions are contagious—and while your partner isn’t the only factor, depressive thinking definitely plays a role in whether your partnership spirals into a distress system or holds strong as a support system.”