Why It's OK to Let Babies 'Cry It Out'

To measure the stress levels of the babies in the study, the researchers analyzed the babies' cortisol levels from cotton swabs of their saliva that the parents collected in the mornings and afternoons. The results also showed that the afternoon cortisol levels in the babies in the two sleeping intervention groups dropped more over time than those of the babies in the control group, indicating less stress, the researchers said.