Pleurisy is a painful medical condition where the thin membranes lining your lungs and chest cavity become inflamed and swollen. These membranes, called the pleura, normally slide smoothly against each other as you breathe, like two pieces of silk sliding together. When you have pleurisy, they become rough and irritated, causing a sharp, stabbing pain every time you take a breath, cough, or sneeze.

The pain often feels worse when you breathe deeply, so people with pleurisy tend to take short, shallow breaths to avoid triggering it. Imagine trying to inflate a balloon inside your chest, but every time you blow air in, it hurts. That's similar to what pleurisy feels like.

Pleurisy usually develops as a complication of another illness, like pneumonia, the flu, or a chest injury. Doctors can treat it with medicine that reduces the inflammation and addresses whatever caused it in the first place. In earlier centuries, before modern antibiotics, pleurisy was much more dangerous and difficult to treat than it is today.