⚠️ Sudden severe breathlessness? Call 911 immediately.
Symptom Guide Physician Reviewed 10 min read

Shortness of Breath: Causes, Warning Signs, and When to Seek Care

Shortness of breath — medically called dyspnea — is the uncomfortable sensation of not getting enough air. It can be a sign of something minor or a life-threatening emergency. Knowing the difference is critical.

AP
Reviewed by Dr. Aisha Patel, MD, FCCP
Board-Certified Pulmonologist · Mayo Clinic

Emergency warning signs — call 911

Call 911 immediately if breathlessness is:

Sudden and severe · With chest pain or tightness · With lips or fingertips turning blue (cyanosis) · At rest with no obvious trigger · With rapid heart rate, sweating, or feeling of doom · After a leg swelling or long journey (possible pulmonary embolism) · In someone with known heart failure who is rapidly worsening

Common causes of shortness of breath

CauseKey featuresUrgency
Pulmonary embolism (PE)Sudden onset; pleuritic chest pain; recent immobility or surgery; leg swelling911 immediately
Heart attack (MI)May be the only symptom, especially in women; with or without chest pain911 immediately
Acute heart failureOrthopnea (worse lying flat); leg swelling; known heart disease911 immediately
PneumothoraxSudden; unilateral; young thin male; sharp pleuritic pain911 immediately
Severe asthma attackWheeze; known asthma; reliever not working911 immediately
PneumoniaFever; productive cough; gradual onset; pleuritic painSame-day care
Asthma (controlled)Wheeze; responds to inhaler; known triggersSee doctor soon
COPD exacerbationKnown COPD; increased cough/sputum; reduced exercise toleranceSame-day care
AnaemiaGradual onset; fatigue; pallor; worse with exertionSee your doctor
Anxiety / panic attackWith tingling, racing heart; improves with calming; no hypoxiaAfter cardiac exclusion
DeconditioningGradual; worse with exertion; improves with exercise trainingGP evaluation

How shortness of breath is assessed

A doctor will assess severity using tools like the MRC Dyspnoea Scale (grades 1–5 based on what activities trigger breathlessness) and measure oxygen saturation with a pulse oximeter. A normal resting SpO2 is 95–100%; below 92% requires urgent assessment and possibly supplemental oxygen.

Key investigations include ECG, chest X-ray, full blood count (anaemia), BNP/NT-proBNP (heart failure), D-dimer and CTPA (pulmonary embolism), spirometry (asthma and COPD), and echocardiogram (cardiac function).

Related conditions

For in-depth information on the most common causes, see our dedicated guides: Heart Disease, Asthma, Anxiety and Depression, and Chest Pain.