Aims: Uncontrolled pain in human infants can lead to permanent damages, so it is important to manage pain for infants. The aim of this study was to determine the effect of breast milk smell on physiological and behavioral responses of the hepatitis B vaccine pain in newborns.

Materials & Methods: In this two-group randomized controlled clinical trial that was performed in 2015, in 9^th of Dey Hospital of Torbat Heydarieh City, Iran, 60 three-day term healthy infants at an age that were supposed to receive the first dose of hepatitis B vaccine were selected by random sampling method and were assigned to 2 test (the breast milk smell) and control groups. In the experimental group, the infants were exposed to the breast milk smell during the vaccination and the control group received no intervention. Data was collected by the checklist of demographic information, registration form of physiological responses and behavioral pain tools (MBPS). Physiological data (heart rate and oxygen saturation) was recorded immediately before and after the intervention by pulse oximeter. Data was analyzed by SPSS 20 statistical software using independent and paired T tests.

Findings: There were no significant differences between the control and the test groups in terms of heart rate mean and oxygen saturation mean before the intervention (p>0.05), but significant differences were observed between them after the intervention (p<0.05). In addition, there was a significant difference between the two groups in the average of behavioral responses after the intervention (p<0.05).

Conclusion: Olfactory stimulation with breast milk has a positive effect on reducing the neonatal pain during hepatitis B vaccination.