A reflex is an automatic instinctive response built into the nervous system that does not require conscious effort to take effect. Almost all of the movement of a baby is reflexive.
If an infant’s cheek is gently touched, it will turn towards the touched cheek and attempt to suck. This is the rooting reflex. The very primitive rooting reflex is present in all mammals and assists the infant and mother with breastfeeding by helping the baby find the mother’s nipple as the breast brushes against its cheek. A baby will do this whether it is hungry or not.
The rooting reflex occurs most in the first four months of life and disappears slowly as the baby grows into a child. This behaviour may then be used as a comfort rather than a reflex, e.g. by sucking on the thumb.