Parents develop long-term disgust habituation, but only after weaning their children

Disgust helps humans avoid potentially pathogenic substances such as bodily effluvia. This reduces illness risks, and is difficult to overcome with cognitive strategies or even through simple habituation in the short term (minutes to hours). Whether habituation emerges in the long-term (months to years) is an unsolved question. Regular professional exposure to disgust elicitors is associated with lower disgust sensitivity and avoidance, but this could be due to selection and survivorship bias. Here, we avoid these limitations by testing a sample of parents (N=99) and controls (N=50) on self-report and behavioural avoidance measures. We used parent-specific items in disgust-sensitivity questionnaires, and child-related stimuli (soiled diapers) in a preferential-looking task. While the control group showed the expected behavioural avoidance, parents of children who were past the weaning stage showed almost no avoidance of stimuli depicting child-related or general bodily effluvia. Curiously, parents whose children had not been fully weaned showed similar disgust avoidance to the control group, even if they had older children who were weaned. These results suggest that parents habituate to disgust induced by faeces in diapers, and that this had generalised to other bodily effluvia. Contrary to our expectations, parents did show disgust avoidance while their (youngest) children were fed only milk, which could point to an adaptive response to reduce the risk of illness in young infants. In sum, continuous exposure to their children’s bodily effluvia inoculates parents to disgust for bodily effluvia, but only after the sensitive milk-feeding stage.