Re-thinking lactation-related nipple pain and damage.

Nipple pain is a common reason for premature cessation of breastfeeding. Despite the benefits of breastfeeding for both infant and mother, clinical support for problems such as maternal nipple pain remains a research frontier. Maternal pharmaceutical treatments, and infant surgery and bodywork interventions are commonly recommended for lactation-related nipple pain without evidence of benefit. The pain is frequently attributed to mammary dysbiosis, candidiasis, or infant anatomic anomaly (including to diagnoses of posterior or upper lip-tie, high palate, retrognathia, or subtle cranial nerve abnormalities). Although clinical protocols universally state that improved fit and hold is the mainstay of treatment of nipple pain and wounds, the biomechanical parameters of pain-free fit and hold remain an omitted variable bias in almost all clinical breastfeeding research. This article reviews the research literature concerning aetiology, classification, prevention, and management of lactation-related nipple-areolar complex (NAC) pain and damage. Evolutionary and complex systems perspectives are applied to develop a narrative synthesis of the heterogeneous and interdisciplinary evidence elucidating nipple pain in breastfeeding women. Lactation-related nipple pain is most commonly a symptom of inflammation due to repetitive application of excessive mechanical stretching and deformational forces to nipple epidermis, dermis and stroma during milk removal. Keratinocytes lock together when mechanical forces exceed desmosome yield points, but if mechanical loads continue to increase, desmosomes may rupture, resulting in inflammation and epithelial fracture. Mechanical stretching and deformation forces may cause stromal micro-haemorrhage and inflammation. Although the environment of the skin of the nipple-areolar complex is uniquely conducive to wound healing, it is also uniquely exposed to environmental risks. The two key factors that both prevent and treat nipple pain and inflammation are, first, elimination of conflicting vectors of force during suckling or mechanical milk removal, and second, elimination of overhydration of the epithelium which risks moisture-associated skin damage. There is urgent need for evaluation of evidence-based interventions for the elimination of conflicting intra-oral vectors of force during suckling.