Disgusting odors trigger the oral immune system

Abstract

Recent research has characterized the behavioral defense against disease. In particular the detection of sickness cues, the adaptive reactions (e.g. avoidance) to these cues and the mediating role of disgust have been the focus. A presumably important but less investigated part of a behavioral defense is the immune system response of the observer of sickness cues. Odors are intimately connected to disease and disgust, and research has shown how olfaction conveys sickness cues in both animals and humans. This study aims to test whether odorous sickness cues (i.e. disgusting odors) can trigger a preparatory immune response in humans. We show that subjective and objective disgust measures, as well as TNFα levels in saliva increased immediately after exposure to disgusting odors in a sample of 36 individuals. Altogether, these results suggest a collaboration between behavioral mechanisms of pathogen avoidance in olfaction, mediated by the emotion of disgust, and mechanisms of pathogen elimination facilitated by inflammatory mediators. Disgusting stimuli are associated with an increased risk of infection. We here test whether disgusting odors, can trigger an immune response in the oral cavity. The results indicate an increase level of TNFα in the saliva. This supports that disease cues can trigger a preparatory response in the oral cavity.

Figure 1.

The figure describes an overview of the experimental procedure including the timing of the saliva samples and disgust measurements. EMG = electromyography.

Figure 2.

Ratings of (a) state disgust and (b) stress are given on a 0 to 10 visual analogue scale (VAS) at three time points (minutes): before (pre) directly after (post) and 30 min after exposure to disgusting or control odors (post30). We find a significant interaction in form of stronger relative increase of state disgust in disgust than control condition from time point pre to post. No such significant interaction effect was found for state stress. SEM: standard error of mean.

Figure 3.

Electromyography (EMG) response recorded at the levator labii (3a) and corrugator supercilii region (3b) are given for the time 6 s around odorant presentation (0 s). Baseline corrected mean levels for 12 time windows (each 0.5 s duration) are given from ‘Disgust’ and ‘Neutral’ exposure conditions showing larger EMG amplitudes during Disgust exposure for the levator labii region and during Neutral exposure for the corrugator supercilii region.

Figure 4.

(a) Salivary TNFα and (b) sIgA levels, sampled before (baseline) directly after (post) and 30 min after exposure to disgusting or control odors (post30). Mean values and standard error of means are given for logarithmic data corrected for salivary secretion rate. We find a significant interaction for TNFα in form of stronger relative increase of TNFα levels in disgust than control condition from time point pre to post.