Cellulitis is a diffuse infection of the soft tissues with no localized area of pus amenable to drainage. The affected area is described as indurated (i.e., warm, red, and swollen). It is also painful. A component of lymphangitis (infection involving the lymphatics) is indicated by red streaking, progressing proximally from the affected area.

An abscess is a localized collection of pus, often with a component of surrounding cellulitis (with the above signs). One sign of an abscess is an area of fluctuance; that is, when you apply gentle digital pressure over the area, you can push and feel a “give,” indicating the presence of fluid underneath. Another sign is that an abscess often seems to “point;” that is, the skin starts to thin from the pressure of the fluid underneath. The distinction between cellullitis and abscess is important. The main treatment for an abscess is incision and drainage (cutting into the abscess and widely opening the abscess cavity). Cellulitis does not warrant this intervention.