They are literally curled in a ball and not at all comfortable when straightened out. The sling holds a baby in this flexed position. Movement stimulates the baby's ability to pull our of this little ball into extension. An infant who cannot see or feel or hear its caregiver has more stress hormones circulation through its central nervous system. This causes the baby to cry.
Stress irritates the immature digestive system, causing baby to spit up and increases diaper rashes.
Being touched and carried has a positive effect on the digestive system. The Over the Shoulder Baby Holder has a shoulder pillow instead of straps over the parent's shoulders. This is especially important for a nursing mom, because the straps can restrict circulation in a nursing mother's engorged chest tissues, causing plugged milk ducts, increasing the incidence of breast infections. Also, the sling allows mom to nurse more on demand because the baby is right next to mom, which also reduces breast infections. With a conventional baby carrier, baby's weight is carried on the parent's shoulder.