trigger an inflammatory response, which draws large numbers of white blood cells to the area and increases the regional blood flow. The final structure of the abscess is an abscess wall, or capsule, that is formed by the adjacent healthy cells in an attempt to keep the pus from infecting neighboring structures. However, such encapsulation tends to prevent immune cells from attacking bacteria in the pus, or from reaching the causative organism or foreign object. Diagnosis An abscess is a localized collection of pus (purulent inflammatory tissue) caused by suppuration buried in a tissue, an organ, or a confined space, lined by the pyogenic membrane. Ultrasound imaging can help in a diagnosis. Classification Abscesses may be classified as either skin abscesses or internal abscesses. Skin abscesses are common; internal abscesses tend to be harder to diagnose, and more serious. Skin abscesses are also called cutaneous or subcutaneous abscesses. IV drug use For those with a history of intravenous drug use, an X-ray is recommended before treatment to verify that no needle fragments are present. If there is also a fever present in this population, infectious endocarditis should be considered. Differential Abscesses should be differentiated from empyemas, which are accumulations of pus in a preexisting, rather than a newly formed, anatomical cavity. Other conditions that can cause similar symptoms include: cellulitis, a sebaceous cyst, and necrotising fasciitis. Cellulitis typically also has an erythematous reaction, but does not confer any purulent drainage. Treatment The standard treatment for an uncomplicated skin or soft tissue abscess is the act of opening and draining. There does not appear to be any benefit from also using antibiotics in most cases. A small amount of evidence did not find a benefit from packing the abscess with gauze. Incision and drainage The abscess should be inspected to identify if foreign objects are a cause, which may require their removal. If foreign objects are not the cause, incising and draining the abscess is standard treatment. In critical areas where surgery presents a high risk, it may be delayed or used as a last resort. The drainage of a lung abscess may be performed by positioning the affected individual in a way that enables the contents to be discharged via the respiratory tract. Warm compresses and elevation of the limb may be beneficial for a skin abscess. Antibiotics Most people who have an uncomplicated skin abscess should not use antibiotics.