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Roughly 20,000 times a day, your lungs quietly get on with the job. Air in, oxygen across a membrane thinner than a soap bubble, carbon dioxide out. You don’t feel any of it until something goes wrong.
That’s the trouble with lungs. They have enormous reserve. You can lose a third of your lung function and notice nothing more than getting a bit puffed on the stairs. By the time a symptom shows up, the disease has usually been there a while.
The seven conditions below cover most of what actually fills respiratory clinics. Some are common and manageable, some are life-threatening within hours. All of them are worth knowing about, if only so you recognise the early signals in yourself or someone you live with. If you want the wider picture first, our plain-English guide to respiratory diseases maps the territory from asthma through to COPD.
1. Asthma: airways that overreact
Around 260 million people worldwide have asthma, and roughly half of them are adults. It is not a childhood illness you simply grow out of.
Asthma inflames the small airways and makes the muscles around them twitchy. Triggers vary wildly between people: cold air, pollen, dust mites, exercise, a chest infection, even strong emotion. When a trigger lands, the airway narrows, the lining swells, and mucus thickens. That’s the wheeze, the tight chest, the cough that won’t settle at night.
The important detail is that asthma narrowing is reversible. A reliever inhaler works within minutes because it relaxes the muscle. A preventer inhaler, taken daily, calms the inflammation underneath. People who only ever use the blue reliever and skip the preventer end up in hospital more often than they need to.
2. COPD: the slow narrowing people dismiss as ageing
Chronic obstructive pulmonary disease covers emphysema and chronic bronchitis, and it is now the third leading cause of death worldwide. Smoking drives the majority of cases, though long-term dust, fumes, and air pollution account for a meaningful slice too.
In emphysema, the delicate air sacs lose their elasticity and merge into larger, floppier spaces. Oxygen transfer drops. In chronic bronchitis, the airway glands enlarge and produce mucus most mornings for months on end. Most people with COPD have a mix of both.
The classic story is someone in their late fifties who has cut down on walking because of “a touch of bronchitis every winter.” By the time they see a doctor, their FEV1 (the volume they can force out in one second) might be half of what it should be. Spirometry takes ten minutes and settles the question. Inhalers, pulmonary rehab, and quitting smoking all slow the decline. Nothing reverses it. Smoking sits behind so much of this that we went deeper into which cancer risk factors genuinely move the needle, and the same list applies here almost word for word.
3. Pneumonia: an infection that floods the air sacs
Bacteria, viruses, or fungi get into the lower airways and the immune response fills the air sacs with fluid and pus. That’s why pneumonia shows up on an X-ray as a white patch where there should be black air.
Symptoms tend to arrive fast: fever, a productive cough, breathlessness, sometimes a sharp pain when you breathe in. Older adults can skip the fever entirely and just become confused or unsteady on their feet, which is why pneumonia in the over-65s often gets missed at first.
It remains the leading infectious cause of death in children under five, killing roughly 700,000 a year. Vaccines against pneumococcal bacteria, flu, and RSV for older adults cut the risk considerably. Most healthy adults recover in two to three weeks, but a cough can linger for six.
4. Lung cancer: the quietest start of the seven
Lung cancer kills about 1.8 million people a year, more than any other cancer. Part of the reason is timing. There are no pain nerves inside the lung tissue itself, so a tumour can grow for months without announcing itself.
When symptoms do appear, they’re easy to explain away: a cough that has changed character, a bit of blood in the sputum, hoarseness, unexplained weight loss, or a chest infection that keeps coming back in the same spot. Those are exactly the kind of creeping, easy-to-dismiss signals we covered in the early warning signs of cancer worth acting on.
Screening has changed the odds for high-risk people. Annual low-dose CT is recommended for adults aged 50 to 80 with a 20 pack-year smoking history who still smoke or quit within the past 15 years. It catches tumours small enough to cure surgically. Our breakdown of what each cancer screening test actually finds explains why low-dose CT is a genuinely different test from a standard chest X-ray.
5. Pulmonary fibrosis: scarring that doesn’t undo itself
In pulmonary fibrosis, the thin, elastic tissue between the air sacs is replaced by stiff scar tissue. Oxygen has a much harder job crossing it. The most common form, idiopathic pulmonary fibrosis, has no clear cause, though smoking, acid reflux, certain drugs, and occupational dust exposure raise the risk.
The signature symptom is a dry, hacking cough plus breathlessness that creeps in over months. Many people first notice it climbing a hill they used to manage easily. Clubbed fingertips, where the nails curve downward, appear in a proportion of cases. A walking oxygen test often shows levels dipping below 88%.
Two antifibrotic drugs, pirfenidone and nintedanib, slow the decline but don’t stop or reverse it. Median survival without a transplant sits somewhere between three and five years from diagnosis. That makes early referral to a specialist centre the single most valuable step.
6. Tuberculosis: still the deadliest infection on earth
TB killed around 1.3 million people in 2022, and roughly a quarter of the world’s population carries latent infection. It spreads through the air when someone with active disease coughs.
Active TB typically brings a cough lasting more than three weeks, night sweats, weight loss, and low-grade fever. It can sit quietly in the lungs for years before that happens. Treatment runs six months for drug-sensitive strains, with four antibiotics in the first phase. Resistance develops fast when courses are cut short, which is why adherence matters so much.
7. Pulmonary embolism: a clot that lands in the lungs
This one isn’t an infection or a chronic disease, but it belongs on the list because it kills quickly and gets mistaken for other things. A clot forms in a deep leg vein, breaks loose, and travels to the pulmonary artery, blocking blood flow to part of the lung.
Sudden breathlessness, sharp chest pain worse on breathing in, a racing heart, and coughing up blood are the classic cluster. It affects roughly one in a thousand people a year and is the third most common cardiovascular cause of death after heart attack and stroke. Long flights, recent surgery, pregnancy, cancer, and immobility all raise the risk.
A large clot strains the right side of the heart, which is why prompt scanning matters. The link between lung clots and cardiac strain is covered in more detail in our piece on what the top heart diseases do to your body.
Symptoms that shouldn’t wait for another week
Most coughs are harmless and settle in two to three weeks. Some are not, and the difference is usually obvious once you know what to look for.
- Breathlessness that has changed. If you now stop halfway up the stairs you used to sprint, get it checked, especially if it’s progressed over weeks rather than days.
- Blood in your sputum. Even a streak. Even once. This is a same-week appointment, not a wait-and-see.
- A cough past eight weeks. Chronic cough has real causes: asthma, reflux, COPD, medication side effects, and occasionally something more serious.
- Unexplained weight loss with a cough. That combination deserves a chest X-ray at minimum.
- Sudden breathlessness with chest pain. Call emergency services. This is the pulmonary embolism pattern, and minutes count.
- Chest tightness that wakes you at night. Nocturnal symptoms are a marker of poorly controlled asthma and predict attacks.
- Fingertips that have changed shape. Clubbing is painless and easy to miss, but it points to underlying lung disease.
Here’s the practical part. Spirometry takes about ten minutes, costs little, and gives you a number you can track for the rest of your life. A baseline reading in your forties or fifties is genuinely useful, particularly if you’ve ever smoked or worked around dust. Lungs don’t complain loudly, so the tests have to do the talking. Book the appointment while you’re still only mildly out of breath, because that’s the stage when most of these conditions can still be slowed, managed, or in some cases cured.
