Depression Is Contagious

New findings show the importance of physical contact in depression contagion.

Reviewed by Gary Drevitch

It's been known for a while that depression is contagious: If your roommate is depressed, you are much more likely to become depressed as well. But it has been a bit of a mystery just how this happens. Is it a form of empathy? Is it about chemicals? Or is it about stress?

A new study helps us cut through some of this mystery. It was conducted on mice, not humans. When a non-depressed mouse was put in a cage with depressed mice, after five weeks, it showed increased depressive behavior and hormonal markers indicative of depression. This, in itself, was a novel way of confirming earlier findings that depression is contagious. But the really interesting and novel insights came from the control conditions.

Here is a slightly different condition the research experimented with: Instead of just working with one large cage, they put a transparent dividing wall between the non-depressed mouse and the depressed mice. And in this case, there was no contagion. This strongly suggests that physical contact (or perhaps some kind of chemical transmission) is involved in the process of contagion. Further confirmation of this comes from yet another set of experiments, in which a non-depressed mouse was put in a cage with the bedding of the depressed mice, and researchers noted some depressive behavior, but milder than in the scenario in which the mice all intermingled.

So, physical contact may be the key. But the experimenters tested yet another factor in how depression may spread: stress. Stress is a major factor in developing depression, so one possible explanation would be that what is actually contagious is not depression, but stress. And we have plenty of experimental evidence—most of us also have a lot of personal experience—that stress is, in fact, contagious. Interestingly, stress did not seem to play a role in depression transmission, though. When the non-depressed, non-stressed mouse was put in a cage with stressed, but non-depressed mice, they did not become more depressed. In fact, they often helped to reduce the stress level of the other mice.

This latter result is especially important when it comes to making sense of what follows from all this for us. Humans and mice are very different. While the mice findings are indicative, it is not direct evidence of how things work in humans.

More importantly, it needs to be stressed that it does in no way follow from any of these results that we should avoid the company of depressed people. And this is the point where the last experimental findings are extremely relevant. Physical contact, giving a hug, and holding someone's hands can really help. It can help overcome stress and it can also help with depression. So physical contact is not just a way in which we could risk contagion; it's an important opportunity to make the lives of people around us better.