Quantitative evaluation of mechanical properties of the human body has assumed significance in the medical and nursing care fields in Japan. Therefore, the study the material properties of the soft tissues of the skin for the prevention and countermeasure for skin damage. In this study, participants included 30 puerperal women who gave birth by vaginal delivery and whose infants were admitted to the neonatal intensive care unit. A comparison was made between the 2 groups with 15 women each (experimental and control group). The intervention consisted of providing a Ashiyu to the experimental group. Puerperal breast tension due to strain was measured quantitatively by measuring skin strain. The physiological changes in the breast (puerperal breast tension) associated with the enhancement of lactation function during the postpartum period and the amount of puerperal breast tension due to the intervention of Ashiyu could be quantitatively grasped by skin strain.