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The act of birth and the growth of an infant in consecutive months are critical for the baby’s adaptation from intrauterine life to the relatively dry and gaseous environment. These adaptive changes have not only effects on structural components but also subsequent functional consequences. The formation of acid mantel is important for the integrity and cohesion of the stratum corneum, a key component of an intact epidermal barrier, as well as for multiple defensive functions of the skin. In this chapter, we review the mechanisms in pH development after birth. Furthermore, we focus on different factors affecting skin surface acidity formation such as the pre- and postnatal age and weight, gender and anatomical site.

© 2018 S. Karger AG, Basel

The intact skin accomplishes a competent inside-out and outside-in barrier function since the earliest stages of an individual’s life [1]. The maturation of the epidermal barrier starts in utero [2] and is completed after birth. The act of birth and the consecutive months are critical for the adaptation from intrauterine life to the relatively dry and gaseous environment. This adjustment is reflected by changes in physiological functions and adaptation of biochemical and biophysical parameters such as skin surface pH, SC hydration and innate immunity. The so-called acid mantel of the epidermis, first described by Heuss at the end of the 19th century, and further investigated around the 1920s by Schade and Marchionini [3], is necessary to regulate defensive functions such as bacteriological, chemical, and mechanical resistance. The pH of the skin shows a bi-phasic behavior (Fig. 1).

Fig. 1. Biphasic pH-gradient of the epidermis with a pH of approximately 5.4 in healthy, non-occluded areas (adult values) and 6.5 at the stratum granulosum, which reaches neutral values of 7.4 in deeper parts of the skin.

The term “newborn” is widely used in research and everyday life for the period immediately after birth. The term “infancy,” originating from Latin (in-fans = unable to speak), is generally defined as the period of nursing that encompasses the first year after birth [4]. However, this term can be applied to young children until the age of 2. “Neonatal” period is a synonym of “newborn” period, which refers to the first month of life. Neonate infants can be full term (born between 37 and 42 weeks of estimated gestational age), premature (born before the 37th gestational week), or postmature (born after 42 weeks of gestation). A classification according to birth weight is additionally accepted for practical considerations.

Before birth, skin has no exposure to external environmental factors or skin care products other than amniotic fluid. Birth marks a sudden transition accompanied by drying and cooling of the skin surface. This biophysical change initiates a cascade of cellular and molecular events leading to an adaptive maturation of defensive functions. Following birth, significant environmental and behavioral factors occur, which may affect skin structure and function, for example, ambient temperature changes, alterations in skin dryness and water content, contact with frictional surfaces such as clothing and blankets. Additionally, parental interactions such as touching, holding and application of skin care products have an influence on skin physiology [5]. It is known that healthy newborns’ skin undergoes progressive changes in epidermal barrier properties over the first months of life [6]. In this chapter, we summarize the knowledge on skin surface pH formation in newborns and the versatile effect of different factors affecting the acid mantel maturation after birth.

Fig. 2. Origin and functional consequences of the acidic pH of the stratum corneum.