The effects of olfactory stimulation and gender differences on pain responses in full-term infants

Studies have reported conflicting findings on whether different smells can reduce distress when infants undergo painful procedures. Our study assessed the impact of vanilla on infants' responses to a painful toe lance, including possible gender differences.

We measured the pain responses of 69 full-term infants - 34 girls and 35 boys - during toe lance, using two multidimensional scales - the Neonatal Facial Coding System and Behavioural Indicators of Infant Pain - together with crying duration and hand movements. Three sets of data were collected during baseline, toe lance and recovery, while the babies were exposed to the odour of vanilla (n = 39) or odourless water (n = 30).

Pain responses increased significantly during toe lance, then declined during recovery. Crying duration correlated significantly with finger splaying/fisting and both pain scale scores, with boys displaying higher pain scores than girls. Vanilla had no impact on pain levels.

Crying and finger splaying/fisting were observable responses that may be useful for screening pain or distress in healthy neonates. Increased pain reactions by boys may reflect higher irritability. Exposure to an unfamiliar odour did not have a calming effect on full-term neonates.