Unconsolable Infant Crying

In human infants, there is an age-related pattern of distress (including fussing, crying and inconsolable crying) that includes increasing daily distress for the first few weeks, usually reaching a peak in the second month, and decreasing thereafter. This distress clusters in the afternoon and evening, includes unpredictable, inconsolable and prolonged crying bouts that are virtually unique to the first four months of life, and is referred to clinically as “colic.” Similar age-related patterns of increasing and then decreasing distress have been described in infant rats, guinea pigs, chimpanzees and free-living Rhesus macaque infants, but prolonged, inconsolable distress bouts have not. In non-human mammalian species, distress usually ceases once direct contact has been re-established between infant and mother, but that is not true in humans. Human distress probably reflects regulation of infant behavioral states in early development, but becomes more of a signal later in the first year. This is less clear for non-human mammals. Regardless of source, distress functions as a signal in all mammals, and results in caregiving responses that can be positive (e.g. increase caregiver investment, nutrition and caring) or negative (abuse). Because crying is a stimulus for feeding, it may contribute to lactational amenorrhea via prolactin stimulation, that in turn contributes indirectly to birth spacing. The effectiveness of crying in stimulating caregiving responses is speculated to improve survival by enhancing mother-infant “bonding” and reducing predation. Alternatively, the increased, prolonged inconsolable crying bouts may increase infanticide, at least in humans. The most significant negative consequence of increased crying in humans is shaken baby syndrome, or infant abusive head trauma.