A sore, more accurately termed an abscess or cyst, is a persistent epithelial cavity filled with fluid or soft material. This cavity typically forms due to internal pressure generated by the accumulation of fluid, which is drawn into the cavity through osmosis. The process begins when tissue damage or infection triggers an inflammatory response, causing white blood cells and other immune components to gather at the site. As the immune system fights off the infection, the cavity fills with pus, a thick fluid composed of dead cells, bacteria, and tissue debris. The growing pressure within the cavity can lead to significant discomfort and pain. If left untreated, the sore may expand, causing further tissue damage and potentially leading to more serious complications. Treatment often involves draining the fluid and addressing the underlying cause to prevent recurrence and promote healing, ensuring that the infection does not spread or worsen.