A skin abscess is a deeper skin infection where a collection of pus forms in the skin. Staphylococcus aureus (staph) and Streptococcus (strep) are two of the more common bacteria that cause skin abscesses. These bacteria enter through compromised skin (cracks, injury, dry skin). The overlying skin becomes red, tender, warm, and swollen over days to weeks and a fever may develop. Abscesses can sometimes form if minor superficial skin infections are not treated appropriately. Most abscesses resolve quickly once appropriately treated. Factors that predispose individuals to developing an abscess include: Any skin infection, especially those that are untreated, diabetes, obesity, intravenous drug abuse, or weakened immune system due to underlying illness or medication.