Snot is produced by the lining inside your nose and sinuses. Specifically, it comes from two sources: tiny mucus-secreting cells scattered across the surface of your nasal lining, and small glands embedded deeper in the tissue beneath it. Your nose churns out roughly 20 to 40 milliliters of this stuff every day, and most of it slides down the back of your throat without you ever noticing.
What Snot Is Actually Made Of
Healthy nasal mucus is about 97.5% water. The remaining sliver is a mix of salts (0.9%), defensive proteins (roughly 1.1%), and long, sticky molecules called mucins (0.5%) that give snot its signature gel-like texture. Mucins are the reason snot stretches and clings rather than running like plain water. They form a mesh that traps dust, pollen, bacteria, and viruses before any of it can reach your lungs.
The protein portion is surprisingly sophisticated. It includes lysozyme, an enzyme that can break apart the cell walls of certain bacteria. Alexander Fleming actually discovered lysozyme in 1921 after drops of his own nasal discharge accidentally contaminated a bacterial culture and killed the growth. Snot also contains antioxidant proteins that neutralize harmful molecules and signaling proteins that help coordinate the immune response. In other words, that slimy stuff in your tissue is a working defense system.
How Your Nose Moves Mucus
Producing mucus is only half the job. Your nasal lining is carpeted with millions of microscopic hair-like structures called cilia, and they beat in coordinated waves 20 to 25 times per second. Each beat has two phases: a fast, strong forward stroke that pushes the mucus along, and a slower return stroke that resets the cilium to its starting position. Hundreds of cilia on a single cell move in synchronized ripples, like a crowd doing “the wave” at a stadium.
This conveyor belt clears particles from your nasal lining in about 10 to 20 minutes. Mucus from deep inside your sinuses drains through small openings into the main nasal cavity, and from there the cilia sweep everything backward toward your throat. You swallow it, and your stomach acid destroys whatever germs hitched a ride. When the system works well, you never feel it happening.
Your Sinuses Add to the Supply
You have four pairs of air-filled cavities, called paranasal sinuses, built into the bones around your nose: behind your forehead, between your eyes, deeper behind your nasal cavity, and beneath your cheekbones. Each pair is lined with the same mucus-producing tissue found in your nose, and each drains into your nasal cavity through its own small opening. Together, these sinuses form a connected drainage network that feeds mucus into your nose continuously. When those drainage pathways swell shut from a cold or allergies, mucus backs up, pressure builds, and you feel it as sinus pain.
Why Snot Ramps Up When You’re Sick
During an infection, your body doesn’t just keep making the usual amount of mucus. The mucus-producing cells multiply, and the glands beneath them kick into overdrive. This is a deliberate immune strategy: more mucus means more trapping surface for pathogens and more delivery of antibacterial proteins to the site of infection. The downside is that your nose becomes a faucet.
At the same time, blood vessels in your nasal lining dilate, causing the tissue to swell. This narrows the airway, which is why you feel stuffed up. The combination of extra mucus and swollen passages forces more of it out the front of your nose instead of draining quietly down the back of your throat.
What the Color Means
Clear snot is normal, baseline mucus. When your immune system responds to an invader, white blood cells flood the area. As they fight and die, they release an enzyme called myeloperoxidase, which contains iron. That enzyme is what gives infected mucus its yellow or green tint. The color deepens as more immune cells accumulate, so thicker green mucus generally means a more active immune battle, not necessarily a more dangerous infection.
A common misconception is that green snot automatically means a bacterial infection requiring antibiotics. In reality, viral infections produce green mucus too. The color reflects immune cell activity, not the type of germ involved.
Why Cold Weather Makes Your Nose Run
Cold air triggers a runny nose even when you’re perfectly healthy. When you breathe in frigid air, your nasal lining loses moisture rapidly as it works to warm and humidify the air before it reaches your lungs. Nerve endings in the nose detect this moisture loss and fire off a reflex signal that tells the glands to produce more fluid. This is essentially your body scrambling to replace the water it just lost to the dry, cold air.
The response kicks in within minutes of stepping outside and fades quickly once you’re back indoors. People with allergies or chronic nasal sensitivity tend to have an exaggerated version of this reflex, which is why some people’s noses drip constantly in winter while others barely notice.
Why Crying Gives You a Runny Nose
This one has nothing to do with mucus production. Your tear ducts connect directly to your nasal cavity through a channel called the nasolacrimal duct. Tears are made by a gland tucked into the upper outer corner of your eye socket. Normally, a small amount of tears coats your eye, drains through tiny openings in your eyelids near the nose, travels through narrow channels, and empties into the nasal cavity. You never notice because the volume is tiny.
When you cry, the volume of tears overwhelms the drainage system. Excess tears spill down your cheeks, but a significant portion still funnels through the nasolacrimal duct and pours into your nose. What feels like a sudden flood of snot is mostly tears arriving through a back door. That’s why the “snot” during a good cry is often thinner and more watery than what you’d produce during a cold.