👉 A nasty fluid, often referred to as serous or serous effusion, is an abnormal accumulation of fluid in body cavities, such as the abdominal cavity, pleural space, or pericardial sac. This fluid is typically clear and watery, but in cases of inflammation or infection, it can become cloudy, bloody, or even thick and yellowish-green. This condition can be caused by various factors, including infections, autoimmune disorders, cancers, or trauma, and it can lead to discomfort, breathing difficulties, or organ damage if not properly diagnosed and treated.