Everyone makes snot. Snot is mucus, a sticky, slimy stuff that the nose makes, and clear, thin mucus is normal and healthy. The nose and sinuses make about a quart (about 1 liter) of it every day, although as of November 2026 experts say nobody knows the exact amount. It is easy to call mucus gross and move on, but it deserves a closer look. Mucus catches dust and germs so they stay out of the lungs, and it keeps the inside of the nose moist.

Mucus is made of water, surface cells, dead white blood cells, mucin and mineral salts. Another description lists water, mucin proteins, defense proteins and salt. In healthy airway mucus, water makes up about 98 percent of the mass, and mucins make up about 0.7 percent. Salts and a few other large molecules make up the rest. So the thing that feels so thick is almost entirely water, held in place by a very small amount of protein. Cells in the mouth, throat, nose and sinuses make it.

The mucin is the main part of mucus, and it gives mucus its gel-like feel. Goblet cells, shaped a bit like a fancy drinking glass, make it. Mucin gets its slipperiness from sugars attached to a protein backbone, and those sugar chains make up more than 70 percent of the mass of the mucins in airway mucus. The sugars give a mucin a brush-like shape. Without them, the protein folds into a ball and has less space to hold water. In MIT friction tests, a solution containing mucins was several orders of magnitude slipperier than a solution that held only salts.

Mucins are packed dry inside goblet cells. After release they must soak up more than 100 times their own mass of water to turn into the right kind of gel for the cilia to move. In MIT lab tests, the coating mucin formed on a surface was 90 percent water. The ability of mucin to hold large amounts of water is critical to keeping the cells that line the body healthy. Mucus needs water because cilia need the airways to stay hydrated to work properly.

Airway mucus has two main layers: a sticky gel layer on top, and a watery layer underneath that surrounds the cilia and lets them beat. A thin layer of surfactants sits between the two. The lining of the nose has two main kinds of cells, ciliated cells that sweep and secreting cells that make mucus. Each ciliated cell in the nose carries about 100 to 250 cilia. Cilia are tiny, about 5 to 7 micrometers long, roughly a tenth the width of a human hair, and they move a bit like arms swimming the breaststroke.

The sweeping is constant. Tiny hair-like strands called cilia in the nose wave back and forth all the time, and cilia line the airways and push mucus along, like an escalator. In the nose, cilia clean the nose about five times an hour. A cold virus can slow the cilia in the nose, and the effect can last for several weeks.

Where does the mucus go? Almost all the dust and germs we breathe in get trapped in mucus, and the cilia carry that mucus toward the throat. Scientists once followed this trip with a tiny drop of mildly radioactive fluid placed in the nose. A scanner followed the fluid as the cilia moved it along, a test since replaced by others. When we swallow mucus, it meets stomach acid, which helps destroy the harmful material in it.

Nasal mucus carries antibodies and enzymes, so it works as a chemical shield as well as a trap. The nose is not a sterile place. It has its own community of microbes, called a microbiome. Mucus, the nose's microbes and antibodies together form a front line of defense against infections.

The front of the nose has its own filter. Hairs inside the nostrils help block bigger bits of dirt, and mucus-covered hairs help trap larger particles as they enter the nose. Hairs in the nose grow only in the front part, the vestibule. Pulling out nose hairs can cause a bad infection, so they are best left alone.

What about color? The color of snot alone does not tell you what is going on inside the body. Yellow mucus often shows up at the start of an infection, when white blood cells are working hard. Green mucus shows up when the body fights a more severe or longer-lasting infection, but it is only one clue. Blood can make mucus pink-tinged or streaked with red. Once an illness is over, mucus slowly returns to its normal color.

A booger is dried mucus mixed with bits of dust, pollen and dirt. Picking the nose can make it bleed, and boogers contain lots of germs, so a tissue is a better tool. Blowing your nose into a tissue is a good way to clear out boogers, and a tissue traps germs. Nose picking has a long formal name, rhinotillexomania, and other primates do it too.

Washing your hands with soap and water helps you stay healthy. Washing hands with soap for about 20 seconds is a good length. If soap and water are not handy, the CDC says to use a hand sanitizer with at least 60 percent alcohol (as of November 2026).

Mucus is found in more places than the nose. Mucus lines the inside of the nose and also the lungs and the digestive tract. It coats the stomach in a layer about one millimeter thick, which keeps strong stomach acid from digesting the stomach itself. That is a lot of places for one slippery gel to work.

Words to know

• mucin: mucus gel protein
• cilia: tiny sweeping hairs
• microbiome: community of microbes
• antibodies: germ-finding proteins
• hydrated: full of water