A subcutaneous abscess is a pocket of pus formed in the superficial skin as a result of normal skin bacteria infiltrating broken or damaged skin. This type of skin infection develops anywhere on the body, but has a preference for intertriginous areas. A subcutaneous abscess is painful and appears as a swollen, erythematous, and fluctuant mass. The diagnosis is typically clinical unless the abscess is complex, something which would warrant a more extensive workup.
A subcutaneous abscess is a pus-filled cavity located in the superficial skin layers caused by penetration of the skin by bacteria following a cut or other dermal disruption . The implicated pathogens are normal skin flora bacteria   such as Staphylococcus aureus (most common), group A Streptococcus, and anaerobes   . A subcutaneous abscess is circumscribed by tissue containing inflammatory cells and the purulent collection is composed of bacteria, immune cells, and material from the surrounding necrotic subcutaneous tissue . Abscesses and other skin and soft tissue infections (SSTIs) are a common cause of visits to the emergency department and the doctor's office .
A subcutaneous abscess presents as a painful edematous mass with induration . They typically form on regions in the body predisposed to friction, also known as intertriginous areas, although they can appear anywhere . This may manifest as a furuncle, which emerges from a hair follicle, or carbuncles which are clusters of infected follicles . Subcutaneous abscesses can rupture spontaneously in which the overlying skin on the abscess thins out and possibly becomes yellow or white, reflecting the pus collection.
Risk factors for abscesses and SSTIs, in general, include advanced age, trauma, diabetes mellitus, malignancy, immunocompromised state, obesity, and so forth   . Additionally, individuals such as athletes playing in close-contact sport and military individuals living in close proximity are predisposed to outbreaks  .
The diagnosis of a subcutaneous abscess is clinical, which is based on patient history and focuses on risk factors and visual inspection of the abscess. Laboratory tests, such as complete blood count (CBC) and blood cultures, are reserved for severe and deep infections . Moreover, blood cultures do not influence the management of simple abscesses, especially in healthy individuals  . Imaging is not required for subcutaneous abscesses or other simple SSTIs .
Note that the workup for complicated SSTIs is extensive and includes needle aspiration of fluid and possibly tissue biopsy . Blood cultures are indicated in patients with systemic involvement, deep tissue infections, and immunocompromised individuals . Furthermore, complicated cases may warrant imaging such as computed tomography (CT) scanning, which is the recommended study . Ultrasonography, magnetic resonance imaging (MRI), and other modalities may be used for further evaluation if needed.