If you ever feel truly, utterly alone, take heart: an invisible entourage never leaves your side.

This hidden, ever-present swarm is called the exposome, and while scientists have only just begun to figure out what populates this constant cloud of chemicals, bugs, and whatnot swirling around you, new research offers an unprecedented glimpse inside.

"People have measured things like air pollution on a broad scale, but no one has really measured biological and chemical exposures at a personal level," says geneticist Michael Snyder from Stanford University.

"No one really knows how vast the human exposome is or what kinds of things are in there."

To find out, Snyder and his team re-engineered a small air-monitoring device, about the size of a pack of playing cards. Over the course of two years, 15 volunteers wore these units strapped to their arm, as it sucked in small puffs of air from their personal orbit and the environment around them.

Every little thing inhaled by the device – bacteria, viruses, chemicals, fungi, and all manner of other particulates – was then extracted for DNA and RNA sequencing and chemically profiled, then catalogued in a custom-built database.

Some participants wore the monitor for a week, others for a month.

Snyder himself strapped one on for a whole two years, and in the end the team had amassed a staggering amount of data on exposome inhabitants – approximately 70 billion readouts.

"Scientists had assembled separate bacteria, viral or fungi databases, but to fully decode our environmental exposures, we built a pan-domain database to cover more than 40,000 species," says one of the team, Chao Jiang.

Participants in the study spent their time across about 50 different locations in the San Francisco Bay Area, but even when they inhabited the same environment, their personal exposome signatures were largely individual.

"It turns out, even at very close distances, we have very different exposure profiles or 'signatures,'" Snyder says.

"The bottom line is that we all have our own microbiome cloud that we're schlepping around and spewing out."

What makes up each person's crowd is of course variable then, but includes numerous traces of their own microbial cloud, plus things like fungi, and particles that have floated in from their immediate environment – such as household pets, chemicals, plants, and so on.

The researchers acknowledge this is only the beginning of this kind of research. In their study, only three individuals wore the device extensively, so there's a limit to how much we can rely upon their results so far.

But already the amount of exposome data gleaned from this technique shows there's a huge amount we can theoretically learn from studying our circulating swarms – and the researchers say if the technology can be made more accessible, it could be an important health and diagnostic tool.

"We want to measure more people in more diverse environments," Snyder says.

"We also want to simplify the technology, ideally to the point that everyone can be out there measuring their own personal exposures – perhaps something like an exposome-detecting smartwatch."

It's early days, but it looks like we could be on the precipice of a transformative new era in health – one that doesn't just peer into your body's internals, but also investigates its immediate external scene: your thriving personal cloud.

"For years we've been sequencing people's genomes, testing their blood and urine, and analysing the microbes in their guts to understand how these things impact human health," Snyder told Wired.

"But all of those things have to do with what's inside your body. The one big thing we're missing is: What are you exposed to?"

The findings are reported in Cell.