In normal breathing, the lungs expand and contract easily and rhythmically within the ribcage. To facilitate this movement and lubricate the moving parts, each lung is enveloped in a moist, smooth, two-layered membrane (the pleura). The outer layer of this membrane lines the ribcage, and between the layers is a virtually imperceptible space (the pleural space), which permits the layers to glide gently across each other. If either of your pleurae becomes inflamed and roughened, the gliding process is impeded and you are suffering from pleurisy. Pleurisy is actually a symptom of an underlying disease rather than a disease in itself. The pleurae may become inflamed as a complication of a lung or chest infection such as pneumonia or tuberculosis, or the inflammation may be caused by a slight pneumothorax or chest injury. The pleural inflammation sometimes creates a further complication by causing fluid to seep into the pleural space, resulting in a condition known as pleural effusion. However, pleurisy is not the only condition that can lead to pleural effusion, it may also be produced by diseases such as rheumatoid arthritis, liver or kidney trouble or heart failure. Even cancer spreading from the lung, breast or ovary can cause pleural effusion. If you have pleurisy, it hurts to breathe deeply or cough, and chest pain is likely to be severe. Accompanying the pain are any other symptoms associated with the underlying disorder. The pain will disappear if a pleural effusion occurs as a consequence of pleurisy, because fluid stops the layers of the pleura from rubbing against each other; however, you may become breathless as the fluid accumulates. In most cases, the risks are those of the underlying cause. A big pleural effusion can compress the lungs and cause breathlessness. Any effusion may lead to empyema. A chest X-ray examination may be required.