My baby doesn't smell as bad as yours:

Abstract 

Disgust is a powerful behavioral adaptation, which confers the advantage of reducing the risk of pathogen infection. However, there are situations in which disgust at core elicitors (e.g., feces) must be modulated in the service of other goals (e.g., caring for a close kin). In Study 1, mothers of infants completed a self-report questionnaire about their reactions to changing their baby's feces-soiled diaper compared with the diaper of someone else's baby. In Study 2, mothers of infants were presented with a series of trials in which they smelled concealed samples of their own baby's feces-soiled diaper and those of someone else's baby. In addition, labels were used to identify the source of the sample (correctly labeled, mislabeled, or no label). Both studies provide evidence suggesting that mothers regard their own baby's fecal smell as less disgusting than that from someone else's baby. Furthermore, labeling had relatively little influence on this effect, and the effect persisted when social desirability was controlled.

Keywords: Disgust, Odor, Disease avoidance, Diapers, Source effect, Evolution