An abscess on the back is a localized collection of pus that forms within the tissues due to an infection. It typically occurs when bacteria, such as Staphylococcus aureus, enter the skin through a cut, hair follicle, or puncture wound. The body’s immune system responds by sending white blood cells to the area, leading to the accumulation of pus—a mixture of dead cells, bacteria, and tissue debris. The area around the abscess usually becomes swollen, red, warm, and painful. If left untreated, the infection can spread, potentially leading to more serious complications. Treatment often involves draining the abscess and administering antibiotics to eliminate the underlying infection.