Interoceptive fears and biased interoception are important characteristics of somatic symptom disorders. Categorization of interoceptive sensations impacts perception of their intensity and unpleasantness. In this study we investigated whether making interoceptive categories threat-relevant further biases interoception of individual sensations compared to safe categories. Either a category containing low- or high-intensity stimuli was made threat-relevant by instructing (and occasionally experiencing) that interoceptive sensations could be followed by an unpredictable electrocutaneous stimulus. We replicated that categorization had a profound impact on perceived interoceptive sensations, with stimuli within categories being perceived as more similar than equidistant stimuli at the category border. We found some evidence for the impact of threat on perceived characteristics of stimuli (with the direction of these effects depending on whether interoceptive stimuli of low or high intensity were threat-relevant), but not for altered categorical choice behaviour. These results imply that the perception of respiratory stimuli is influenced strongly by top-down processes such as categorization, and suggest that interoceptive processing may flexibly adapt to contextual factors such as threat in healthy individuals. However, inflexible responding to repeated and/or severe threat to the internal body may compromise accurate interoception and may result in interoceptive illusions contributing to medically unexplained symptoms and syndromes.