Normally, cortisol is supposed to tamp down the inflammatory response, but the cells of lonely people—and monkeys—aren’t as responsive to the cortisol. It’s like they have internal poison ivy, but not even buckets of anti-itch cream can soothe it.

People who are chronically lonely tend to withdraw socially because they start to feel like other people aren’t trustworthy. Socially isolated people view their interactions with others more negatively, so they keep their distance, perpetuating a cycle of loneliness.183 People who are already lonely, paradoxically, are more likely to lose friends over time. As one paper on this subject notes, “These reinforcing effects mean that our social fabric can fray at the edges, like a yarn that comes loose at the end of a crocheted sweater.”184

That’s why it’s important to acknowledge that though being the sole Russian in West Texas certainly played a role, I brought a lot of my social isolation on myself. After a few of the popular kids made fun of me, I tended to assume they spoke for the masses and avoided all of my classmates—even the ones who probably would have happily befriended a girl with a strange name. I’ve carried this feeling forward into adulthood, at times distancing myself from people out of fear they’ll discover the “truth” about me—I’m an immigrant, surprise!—long after this strategy stopped being rational or useful.

Ultimately, loneliness can spark a number of health problems. Below the skin, the body can’t tell the difference between loneliness and any other type of threat. It perceives loneliness just like it would the possibility of being lanced with your enemy’s spear: something, it thinks, may need to be mended right away. Your body begins to treat loneliness much like it would any other kind of bodily damage, springing into action to try to fend off the millions of bacteria that might be pouring in every second.

Typically, the immune system spends most days fighting a long, slow battle against viruses, the minor colds and sexually transmitted diseases that hop from human to human. When it senses a threat like loneliness, though, the immune system pivots to preparing to fight bacteria instead.

The way the body fights bacteria, somewhat unfortunately for the body, is also through inflammation, explained Steve Cole, a professor of medicine and psychiatry at the UCLA School of Medicine. He described this inflammatory process as one in which immune cells “destroy everything in sight around them,” causing lots of collateral damage. During inflammation, cells called macrophages release dozens of different molecules—proteins called cytokines—to float around and communicate to other cells. White blood cells are summoned to help destroy bacteria. T cells do what Cole calls a “Pac-Man-style chomp” on anything that might have a pathogen inside, even if it’s just healthy tissue.