You're Breathing Human Skin in the Subway

If you've ever felt uncomfortable on a crowded subway platform, wait until you learn what you're actually breathing. Scientists at the University of Colorado analyzed air samples from New York City subway stations between 2007 and 2008 and discovered something unsettling: approximately 15% of the particulate matter floating around you is human skin.

We're not talking about a little dust. That percentage includes skin cells that flake off from the heels and heads of your fellow commuters, along with contributions from belly buttons, ear canals, armpits, and yes—rear ends. Every time someone shuffles their feet or scratches their head, microscopic particles become airborne and join the subway atmosphere you're inhaling.

Why So Much Skin?

Humans are basically walking dust factories. The average person sheds about 30,000 to 40,000 skin cells every hour, and most of us don't even notice. Multiply that by thousands of commuters packed into enclosed underground spaces with limited air circulation, and you've got a recipe for a skin particle soup.

The researchers found that skin particles primarily came from two high-traffic areas: heels (from all that walking and standing) and heads (from scratching, touching, and general movement). About 12% came from those other delightful body regions mentioned earlier, making subway air a surprisingly intimate experience with strangers.

Should You Panic?

Here's the good news: probably not. Despite the gross-out factor, the University of Colorado study concluded they "encountered no organisms of public health concern." The skin particles themselves aren't dangerous—they're just dead cells that your body was going to shed anyway.

Interestingly, when researchers compared the air inside subway stations to outdoor air at Union Square Park, they found minimal differences. The main distinction was higher levels of fungi in the stations, likely from wood rot in the infrastructure. So while you're definitely breathing in your neighbor's epidermis, you're not necessarily breathing in anything more hazardous than what you'd encounter above ground.

What Else Is Down There?

The subway microbiome is actually dominated by bacteria commonly found on healthy human skin. Researchers analyzing metro systems have identified:

• Cutibacterium (15%, mostly C. acnes)
• Corynebacterium (13%)
• Streptococcus (9%)
• Staphylococcus (5%, mostly S. epidermidis)

These bacteria reflect what's naturally living on human skin, saliva, and other body surfaces. No fecal contribution was detected, which is a relief given how many people touch those poles.

The real concern with subway air isn't the human skin—it's the metal particles from wheel and brake wear. Studies have shown that particulate matter in underground railways is approximately eight times more genotoxic and four times more likely to cause oxidative stress in lung cells compared to outdoor urban air. Those iron-rich particles from rail-wheel friction are far more worrying than your fellow passenger's dead skin cells.

The Takeaway

Yes, you're breathing in a fair amount of human skin when you ride the subway. But before you start holding your breath or demanding a hazmat suit, remember that dead skin cells are everywhere—in your home, your office, and definitely in your bed. The subway just concentrates them in one place.

If you're still grossed out, consider this: at least now you have a great conversation starter for your next awkward commute. "Did you know we're all inhaling each other right now?" You'll either make a new friend or get plenty of personal space. Win-win.