Abscesses are serious, localised, skin-deep infections caused by bacteria, commonly Staphylococcus areus. They are more specifically a collection of pus made up of dead neutrophils (which are a type of white blood cell involved in immune response), bacteria and protein. The pus collects in cavities where there are infections or other foreign materials such as piercings.vertical tragus The bacteria kill local cells, which cause cytokines to be released triggering an inflammatory response (cytokines are hormones produced by the cells of the immune system.) Many white blood cells are drawn to the area which increases the blood flow. They start off red and tender, becoming hard and then as it fills with white blood cells it softens and forms a head of pus.