Powered by the diaphragm, abdominal and rib muscles, coughing is highly effective at clearing irritants or mucus from the lungs. Each cough expels thousands of saliva droplets at up to 160km/h (100mph). Each droplet is potentially laden with viruses or bacteria and can travel up to two metres, depending on size.
Researchers at the Massachusetts Institute of Technology, US, have discovered that an invisible gas cloud helps cough droplets to spread around a room. Smaller droplets in the gas cloud are swept around by eddies, travelling further and taking longer to settle.
Coughed droplets can enter the nose or mouth of innocent bystanders. Meanwhile, germs in settled droplets can live on some surfaces for hours, ready to transfer to an unsuspecting victim.