About 15 million babies are born preterm every year around the world(Blencowe et al., 2013). This corresponds to more than one in every 10 babies born alive(Lincetto \& Banerjee, 2020). This situation, which is a serious problem all over the world, causes approximately 1 million children to die from complications related to preterm birth before the age of 5 years(Walani, 2020). Many of the living preterm babies also develop psychological and physical problems that require follow-up in adolescence, adulthood or lifelong (Kajantie et al., 2021; Manninen et al., 2022). Compared to term babies, preterm babies continue their lives with lower motor and neurological abilities in the later periods of their lives(Wolke et al., 2019). In addition, unlike full-term babies, hospitalization in the neonatal intensive care unit (NICU) after birth causes them to be exposed to many stress-inducing factors such as noise, nursing intervention and light (Larkin et al., 2019).

Stress is a term used to describe th eresponse of a person to both positive and negative events that he encounters daily throughout his life. Stressors can be physical, emotional, environmental or theoretical. Stressors can all affect the body's stress response equally. Stress response, also known as "fight or flight" response or general adaptation syndrome, includes physiological changes that ocur with an individual's encounter with or perceived stress. This stres response is a result of stimulation of the sympathetic nervous system resulting in a cascade of neuro-endocrine-immune responses, with reproducible physiologic effects that include an increase in respirations, heart rate, blood pressure, and overall oxygen consumption (Franke, 2014). Physiological consequences of stress, hypothalamus-pituitary-adrenal cortisol are regulated. In response to a stressor, there is an increase in the secretion of glucocorticoids, especially cortisol(Gunnar et al., 1991).There are three different types of stress. Positive stress; this type of stress is a normal part of life, a positive and normal stress response, and is essential for a child's growth and development. Positive stress responses are infrequent, short-lived, and mild. Tolerable stress; the stress that can be tolerated is more severe, frequent, or persistent. The body responds to a greater degree, and these biochemical responses have the potential to negatively affect brain architecture. Toxic stress; toxic stress leads to prolonged stimulation of the stress response with the body's inability to fully recover(Bergman, 2019a; Weber \& Harrison, 2019). It differs from a normal stress response because there is a lack of caregiver support, reassurance, or emotional attachment. Inadequate caregiver support prevents the stress response from being supported or the body returning to its initial functions.This stress causes the development of many other problems in addition to the increase in the problems that will develop due to preterm birth in their future lives. Therefore, minimizing this stress is of vital importance for preterm infants and their families (WHO, 2017; Ylijoki et al., 2020).

Studies on stress are generally aimed at young children and infants. However, in the neonatal period, "especially in preterm babies", this issue was not given enough attention and was almost completely ignored. Researching this issue will help to make serious changes and corrections in the working principles of the neonatal intensive care unit. For this reason, this study was planned to determine the effects of Kangaroo Care (KC) and Maternal Odor on preterm infants on Toxic Stress and to create evidence-based recommendations about these practices in the NICU setting.