The benefits of skin-to-skin contact (SSC) derive from a global neurological state, in which intimate maternal-infant physical SSC is the safe and expected environment to foster reproductive fitness. (24) The immediate result is bonding, which is in the short-term expressed physiologically (25), with improved cardiorespiratory and metabolic status. (2) This same bonding is however also the psychobiological root of long-term emotional and social development. (25,26) This is the essence of “buffering protection of adult support”, and absence thereof corresponds to “toxic stress” in the context of early childhood development. (27) The many benefits of SSC are really reflecting the decrease of harms from toxic stress that follows separation.

Recent advances in the understanding of epigenetics and developmental neuroscience (28), along with interpretations from life sciences theory (evolutionary biology) (24,29) and preclinical studies (30), suggest new paradigms for improving neonatal outcomes, and by gentle early newborn care based on parents they suggesting increased attention to the needs of the developing brain, as a basis for better long-term outcomes. (2,31–33) Moreover, a feature of reproduction in primate life sciences theory is SSC, where SSC is the environment or habitat required for epigenetic and neurosensory needs (34), supporting physiological systems for survival. (25) Maternal-neonate separation in primate studies is the most severe form of stress known (35,36), resulting in physiological dysregulation (25), overwhelming  autonomic and neuroendocrine stress-responses (37), with the most severe effects on development and health. (38–40) Decreased resilience is proportional to immaturity, therefore the smaller the infant the greater the potential benefit of SSC. Further it is during the period of transition to extra-uterine life immediately after birth that such regulation has the greatest importance (7), and when failure may result in mortality in low resource settings. (1,18,41)

Several mechanisms may underlie SSC, at the heart of these is the concept of maternal-neonate co-regulation, meaning that mother and neonate in close contact constitute an evolved self-regulating system which, when functioning properly, promotes mutual health and thriving. (25,42–46) This system requires a sense of safety (47) provided by SSC. This self-regulating system comprises ‘hidden regulators’ – physiological, behavioural and psychological signals passed back and forth between mother and infant – that regulate physiology, mood and behaviour towards thriving. (25,45) Regulatory effects of maternal odour (45,48), breastmilk (49) and SSC (50) on human neonatal physiology, breastfeeding, sleep and brain development have been demonstrated. Sleep may be the most powerful factor, as brain development takes place primarily during hourly sleep cycles. (6) Separated infants have disturbed sleep cycles (5), while SSC in infants born preterm promotes sleep cycling (51), and consequently accelerates brain maturation. (8) Similarly, these systems regulate feeding behaviour, and offer frequent opportunities to suckle at the breast, with an umbrella of sensory cues from SSC and promote early establishment of exclusive breastfeeding. (2) Improved temperature control from SSC is achieved, fewer calories are required for thermogenesis and more are available for growth. For stable low birth weight infants, there is good evidence that SSC improves both mortality and morbidity. (1)

Animal and human evidence shows that the regulatory status of physiological systems in early life may become epigenetically programmed for life (13,52–54) and increased risk for long term physiological dysregulation and social maladaptation. (38) This permanent anatomical and physiological embedding is called developmental programming. (53,54) A ten-year follow-up study from Israel provides evidence of a long-lasting benefit from early SSC in both physiologic organisation and in cognitive control. (14) The ‘hidden regulators’ may be involved in establishing a number of biological rhythms (brain oscillators), that control the social vagus (parasympathetic), cortisol reactivity (sympathetic) and the sleep-wake cycle (state organisation). (55) The early settings of these may contribute to an ongoing advantage in development, ensuring a more secure maternal-infant attachment, with increasing benefit over time. (14)

Newborn infants, through their behaviour, vocalisations (56), and odours (48) also exert powerful regulatory influences over mothers and fathers. These regulatory mechanisms are reflected in the response patterns of hormones, e.g. oxytocin (57),  testosterone, prolactin, and brain activity in mothers (26), and fathers. (57,58) SSC is important for fathers and their involvement enables continuous SSC. (59–61) Other close family members may also contribute. (62)
Attention to SSC technique is important. Key features are ensuring actual skin contact with no other clothing at all between infant and adult skin, and ensuring that the airway is secured and protected. There is no technology that contra-indicates the use of SSC, however a skill set is needed that ensures patient safety is protected at all times.

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