Many different agents cause abscesses. The most common are the pyogenic, or pus-forming bacteria, such as Staphylococcus aureus, which is nearly always the cause of abscesses directly under the skin. Abscesses are usually caused by organisms that normally inhabit nearby structures or that infect them.

For example, abscesses around the anus may be caused by any of the numerous bacteria found within the large intestine. Brain abscesses and liver abscesses are caused by the bacteria, amoeba, and fungi that are able to travel there through circulation.

Symptoms of an abscess are the general signs of inflammation. Symptoms that identify superficial abscesses include heat, redness, swelling, and pain over the affected area. Abscesses in other places may produce only generalized symptoms, such as fever and discomfort.

A sterile abscess may present as painful lump deep under the site of an injection. A severe infection may bring on fever, fatigue, weight loss, and chills. Recurrent abscesses may indicate undiscovered allergies or decreased immune functioning.

A general physical examination and a detailed patient history are used to diagnose an abscess. Recent or chronic disease or dysfunction in an organ suggests it may be the site of an abscess. Pain and tenderness on physical examination are common findings. There may also be a leakage of pus from a sinus tract connected to an abscess deep in the body tissue.

Infections that are treated early with heat, if superficial, or antibiotics, if deeper, will often resolve without the formation of an abscess. It is even better to avoid infections altogether by promptly cleaning and irrigating open injuries, particularly bites and puncture wounds.