The purpose of this paper is to present contaminated interaction as a design construct. Interactions with an object can be altered, positively, neutrally or negatively, due to some prior use. In such cases, the interaction departs from the designed condition and is said to be contaminated. This is particularly significant as objects, physical or non-physical, have multiple uses or are shared amongst users. We propose an ontological model of contaminated interaction based on a review of literature and an analysis of user experiences. The model outlines the process of contaminated interaction including the drivers and outcomes. In a negative context, contamination can lead to consumers misusing, negatively experiencing, or avoiding the object altogether. Positive contamination sees the opposite effect in which usability can increase, users report more positive experiences and users seek out or cherish the object. Together, this model presents an approach to understanding and addressing contamination in the design process to enable the creation and maintenance of meaningful experiences.