Pleural effusion means extra fluid has built up in the space between your lungs and your chest wall. That space is normally paper-thin, so even a small amount of liquid can press on the lung and trigger clear, easy-to-notice symptoms.

The most common complaint is a dull ache or tight feeling in the chest that gets worse when you take a deep breath, cough, or laugh. Many people notice they’re short of breath after walking up stairs or carrying groceries—activities they handled easily before. The shortness can feel like you can’t fully fill your lungs or like you’re breathing through a straw. A dry, hacking cough often shows up next; it’s your body’s attempt to clear the pressure, but nothing comes up.

If an infection is the cause, you may run a fever, feel chilled, or notice thick green or yellow phlegm. Larger effusions can cause the chest to feel heavy or lopsided, and some people hear a rubbing or squeaking sound when they breathe. In severe cases the shoulder on the affected side may ache, and you can feel your heart racing even when you’re sitting still.

Because these signs mimic a chest cold or even heart problems, many people wait too long to get checked. Any new chest pain with shortness of breath that lasts more than a day deserves an imaging scan.