Your turn
Each lab is one step from the video. Change things and see what happens.
Each lab isolates one part of the story. The models are simplified to show the idea; they are not medical tools.
Tap the buttons and see what happens.
Switch between a wide tube and a thin straw. How much air gets through?
Narrow the tube and watch the airflow fall much faster than the width.
Tap the wide tube, then the thin straw. Which is easier?
Tap a tube on the tree. Which ones have stiff rings, and which have a muscle wrap?
Cartilage helps hold the larger airways open. Bronchioles have no cartilage; smooth muscle in their walls can change their width.
Tap a tube. What does it look like inside?
Switch on each change. Which one cuts the air flow most? What about all three?
Each change shrinks the open radius; flow falls roughly with the radius to the fourth power.
Tap the buttons. How does the tube get smaller?
A simplified model: real airways vary, and the flow rule is an idealised textbook law.
Send a trigger into both airways. Which one reacts?
The same harmless trigger: a normal airway ignores it, a hyperresponsive one narrows.
Send pollen or pet dander. Which tube makes a fuss?
Switch factors on and off. Does the chance ever reach "certain"?
Risk factors raise the chance, but none guarantees asthma. People can get asthma with no family history.
A picture of the idea, not a real risk calculator.
Add triggers, then use each inhaler. Which one fixes the squeeze, and which one calms the swelling?
A reliever relaxes the muscle within minutes; a daily preventer lowers inflammation and sensitivity over time.
Add a trigger, then use the puffers. What happens?
Not medical advice. Talk to a doctor about an asthma action plan. If a reliever isn't helping, or breathing is still very hard, get emergency help.
Asthma is something some people have in their air tubes. Lots of kids and grown-ups have it. Sometimes, breathing can feel like breathing through a thin straw.
Air goes down one big tube in your chest. Then the tubes split again and again, like an upside-down tree. The tiny tubes have a soft muscle all around them, like a hug. Inside, a wet layer makes sticky goo that catches dust.
With asthma, the tiny tubes are extra touchy. Sometimes the muscle hugs too tight, the inside puffs up, and it makes extra goo. Then the air has less space. You might cough, or hear a little whistle when you breathe out.
Things that make the tubes act up are called triggers. Flower dust, tiny dust bugs, tiny skin flakes from pets, cold air, smoke and colds can all be triggers. Every person has their own.
A blue puffer, called a reliever, helps the muscle let go. A preventer puffer, used every day, helps the tubes calm down. People with asthma can run, swim and play. One runner with asthma even set a world record!
This page explains how the body works; it isn't medical advice. If you think you or someone else has asthma, talk to a doctor or nurse.
Nobody knows the exact cause of asthma, and it may be different from person to person.212 What scientists do know is what happens: in asthma, the airways in the lungs are a little swollen and extra sensitive, even on a good day.10 When something sets them off, three things narrow the tubes:210
Air then has to squeeze through a narrow gap, which causes wheezing, coughing, shortness of breath and a tight chest.3 Why some people's airways are sensitive in the first place isn't fully known, but genes and surroundings likely play a role: family history, allergies, early chest infections, smoke and pollution.215
Asthma is a long-term (chronic) condition that affects the airways, the tubes that carry air in and out of your lungs. With asthma, the airways can become inflamed and narrowed at times, which makes it harder for air to flow, especially when you breathe out.1 Symptoms usually come and go, and between flare-ups many people feel completely normal.311
It is very common. About 1 in 13 people in the United States have asthma: roughly 25 million people, including about 4.7 million children (CDC, 2021 data).18 It often starts in childhood, but it can begin at any age.110
Your airways look like an upside-down tree.6 Air goes down the windpipe (trachea), which splits into two bronchi, one for each lung. These branch again and again into tiny bronchioles, each about 1 millimetre across.16
The windpipe and bronchi are held open by stiff rings of cartilage. Bronchioles have no cartilage. Instead, their walls are muscular, and that muscle can change the size of the tube.16 The inside is lined with a moist layer containing cells that make mucus, a sticky film that normally traps dust so it can be swept away.16 Asthma happens in exactly these two places: the muscle and the lining.16
| Change during a flare-up | What it does | What helps it |
|---|---|---|
| Muscle tightens (bronchospasm) | Squeezes the tube from outside, like a hand on a hose | Reliever inhaler: relaxes the muscle within minutes13 |
| Lining swells (inflammation) | Thickens the wall, so the opening shrinks from inside | Preventer inhaler: calms inflammation over time13 |
| Extra mucus | Sticky mucus clogs the space that's left | Calming the inflammation; avoiding triggers5 |
The width of a tube is the main thing that decides how easily air flows through it.17 And the effect is much bigger than you might expect. For smooth flow, the resistance of a tube depends on its radius raised to the fourth power, so narrowing a tube by only about a sixth (16%) can cut the flow in half.18 Real airways are messier than a physics textbook tube, but the lesson holds: a little squeezing goes a long way.
flow ∝ radius⁴ so 16% narrower ≈ half the flow
Other conditions can cause these too, but in asthma they tend to follow a pattern: they come and go, get worse with colds, are set off by things like exercise, allergies or cold air, and are often worse at night or in the morning.3 During a bad flare-up (an asthma attack), some people say it feels like trying to breathe through a straw.4
A trigger is anything that sets off or worsens symptoms in airways that are already sensitive.2 A calm airway meets a speck of pollen and ignores it. A sensitive airway overreacts to something that is usually harmless and narrows too much.2 Common triggers include:2712
Everyone's triggers are different, and they can change over time.715 Knowing your own triggers and avoiding them where you can is a big part of keeping asthma under control.7
Triggers explain a flare-up. They don't explain why someone's airways became sensitive in the first place. That's the real "cause" question, and scientists are still working on it.214 Asthma often begins when the body's defence system reacts strongly to something breathed into the lungs, usually in childhood while that defence system is still taking shape.2 Many things can work together to make that more likely:
None of these is a sure thing. Having someone with asthma in the family doesn't mean you'll get it, and people can get asthma with no family history at all.14
Asthma can start for the first time in adulthood, called adult-onset asthma.2 Common reasons include:
Sometimes childhood asthma fades as the lungs grow, then comes back later in life.10
There's no cure for asthma yet, but treatment controls it well enough for most people to live a normal, active life.113 The main treatment is medicine you breathe in through an inhaler, and the two main kinds fix different parts of the problem:13
Doctors also help each person write an asthma action plan: which triggers to avoid, how to spot a flare-up, which medicine to take when, and when to get help.5 Needing a reliever three or more times a week is a sign to check in with a doctor or nurse.13
Yes. With treatment, people with asthma should be able to stay active, and warming up and training regularly can help.25 Asthma is actually common among elite athletes, especially in endurance sports like swimming, running and cycling, and many compete at the Olympics on equal terms with everyone else.19
British runner Paula Radcliffe was diagnosed with asthma at about 14 after getting dizzy and breathless in training. She learned to use inhalers and a peak flow meter, and went on to set the women's marathon world record (2:15:25) in 2003. Her message to young people with asthma: "control your asthma and not let it control you."20
Nobody knows the exact cause, and it may differ from person to person. A mix of genes and surroundings raises the chance: a parent with asthma, allergies such as hay fever or eczema, chest infections in early childhood, breathing smoke or polluted air, and (in adults) dusts or chemicals at work.
A cause is the underlying reason someone's airways became sensitive in the first place. A trigger is something that sets off symptoms on a particular day, like pollen, dust mites, pet dander (tiny skin flakes from furry pets), cold air, smoke, a cold or hard exercise.
The main signs are wheezing (a whistling sound when you breathe out), coughing (especially at night or early morning), shortness of breath and a tight chest. They tend to come and go. A doctor or nurse can check whether you have asthma, often with a breathing test called spirometry.
Asthma can start at any age. Common reasons for adult-onset asthma include dusts or chemicals at work, hormone changes, smoking and being very overweight. Sometimes childhood asthma that faded comes back later.
No. Asthma is about sensitive, inflamed airways that narrow at times, and between flare-ups breathing can be completely normal. Asthma that stays poorly controlled for a long time can thicken the airway walls, which is one reason good treatment matters.
Partly. If a parent has asthma, a child is three to six times more likely to develop it. But it's not a sure thing: many people with a family history never get asthma, and some people get it with no family history at all.
Yes. With the right treatment, people with asthma should be able to stay active. Warming up and using a reliever before exercise (if a doctor advises it) can help. Many Olympic athletes have asthma, including Paula Radcliffe, who held the women's marathon world record from 2003 to 2019.