Take a breath through your nose. At any moment you breathe mostly through one nostril while the other rests, and the busy side switches about every two hours. This is the nasal cycle. Behind this quiet job sits a lot of snot. Let's find out what it is doing.

Snot is mucus, a sticky, slimy stuff that the nose makes. Cells in the mouth, throat, nose and sinuses make it, and it keeps the inside of the nose moist. Clear, thin mucus is normal and healthy, and everybody makes it. That is a good start, but what is the stuff made of?

What is mucus made of? Mucus is made of water, mucin proteins, defense proteins and salt. Mucin is the main part, and it gives mucus its gel-like feel. Goblet cells, shaped a bit like a fancy drinking glass, make mucin. Let's take that one piece at a time, and see how it goes.

Airway mucus has two main layers. A sticky gel layer sits on top, and a watery layer underneath surrounds the cilia and lets them beat. Cilia are tiny hair-like strands that wave back and forth all the time. They line the airways and push mucus along, like an escalator. They sweep the mucus, with the stuff it has caught, toward the throat.

What is all that sweeping for? Sometimes viruses and bacteria float in the air we breathe, and the nose traps many of them. Hairs inside the nostrils help block bigger bits of dirt, and mucus-covered hairs help trap larger particles as they enter the nose. Almost all the dust and germs we breathe in get trapped in mucus. So where does all of that go next?

Mucus holds antibodies, which are proteins that help the body find germs. It lines the nose, the lungs and the digestive tract, and when we swallow mucus, it meets stomach acid, which helps destroy the harmful material in it. As of November 2026, experts say the nose and sinuses make about a quart, or about 1 liter, of mucus every day, but nobody knows the exact amount.

Let's look at one more thing that gets into the nose, which is pollen. You may have heard that hay fever comes from hay and gives you a fever. In fact, hay fever is an allergy to pollen, the fine powder plants make. It is also called seasonal allergic rhinitis, and it is caused by pollen from trees, grasses and weeds. It can bring sneezing and a runny nose.

What does the body do when pollen sets off hay fever? It releases a chemical called histamine, and histamine causes the runny nose, sneezing and swelling. Hay fever tends to come back at the same time every year, and in the UK it is usually worse between late March and September.

A runny or blocked nose is also a main sign of a cold, and a cold usually gets better on its own in about one to two weeks. How do colds spread? Colds are spread by germs from coughs and sneezes, which can land on hands and surfaces. Washing hands helps stop respiratory infections from spreading. Washing hands with soap for about 20 seconds is a good length, and washing your hands with soap and water helps you stay healthy. So who is ready for a quick look at the last big question?

What about boogers? A booger is dried mucus mixed with bits of dust, pollen and dirt. Blowing your nose into a tissue is a good way to clear them out, and a tissue traps germs. Picking the nose can make it bleed, and boogers contain lots of germs, so a tissue is a better tool. And one more fact about snot: the color of snot alone does not tell you what is going on inside the body.

Words to know

• histamine: allergy chemical
• cilia: tiny sweeping hairs
• nasal: of the nose
• pollen: plant powder
• antibodies: germ finders