Background/aim Hospitalised newborns are highly exposed to nosocomial odorous substances (OS) triggering possibly the intranasal trigeminal subsystem. Irritation of the nasal mucosa can induce pain and activations in pain processing areas in adults We aimed to evaluate cortical activation in trigeminal/olfactory and pain areas following OS exposure in newborns.

Methods Forty-four newborns (17 full-terms, 12 preterms at term PMA and 15 preterms <33 weeks PMA when tested) were exposed in controlled conditions (silent room, active sleep, randomised order) to three odours presented on a Q-tips:

– water (control);

– a hand rub (DES60^®) diluted to match the odour’s intensity released by hands;

– an adhesive remover (Convacare^®).

We recorded bilaterally cortical activation in orbito-frontal gyri (OFG), prefrontal (PFC) and somatosensory (S1 and S2) cortices during 40s (10s-baseline, 10s-presentation, 20s-post-stimuli) by multichannel-NIRS. HbO2 changes were analysed from baseline (ANOVA) and by subgroups (Kruskall-Wallis).

Results In the whole population, we observed:

– no activations for water.

– cortical activations (HbO₂ increase) for DES60^® (p < 0.001), unilaterally in OFG, PFC, and bilaterally in S1 and S2; whereas only in S1 (unilaterally) for Convacare^® (p < 0.001).

We noticed significant profiles of response for all infant’s subgroups, in at least one olfactory and one pain processing areas. The average magnitude of HbO₂ increase from baseline was higher in full-terms vs both subgroups of preterms: 8.5(2.8–12.6) µmol/l vs 5.9(2.6–10.4) and 5.7(1.8–9.2) µmol/l for DES60^® (p < 0.001).

Conclusion Full-term and preterm newborns can perceive OS at a cortical level. Exposure to OS can activate trigeminal/olfactory and pain processing areas and may induce discomfort/pain in newborns.