Research Highlights
The following research is in process at the
Skin Sciences Institute at Children's Hospital Medical Center of Cincinnati:
The late gestational human fetus develops physiological mechanisms for successful transition from aqueous surroundings in utero to a dry, terrestrial environment at birth. They include adaptation to air breathing and enteral nutrition, elimination of wastes, and maintenance of body temperature and water balance. The in utero development of a relatively impermeable cutaneous barrier, the stratum corneum, is key to this transition. Terminal differentiation of keratinocytes and the biosynthesis of lipids give rise to the stratum corneum.
During the last trimester the human fetus lays down the vernix caseosa, a proteolipid biofilm that surrounds the nascent stratum corneum and creates the primary interface between the fetus and the amniotic fluid. In both the neonatal rat and the human, we have shown that intrauterine skin barrier formation results in a dry skin surface at birth. The surprising feature of this barrier is that it develops under conditions of total fluid immersion. For an older infant or an adult, continuous exposure to water is completely deleterious to stratum corneum integrity and function.
We have demonstrated in both the neonatal rat and the human that the skin surface is covered with a hydrophobic lipid film at birth. We hypothesize a potential mechanism whereby the development of a surface hydrophobic layer in utero creates a "dry" upper surface allowing cornification of the underlying keratinocytes with formation of a highly functional epidermal barrier. At birth, this hydrophobic mantle provides protection against evaporative heat loss and microbial invasion. A major role for the sebaceous gland is suggested and this may be relevant to the development of various skin conditions later in infancy and adolescence. We hypothesize that the human stratum corneum exhibits a series of programmatic changes in endogenous hydration and surface water binding, which are linked to visible signs of surface drying, such as scaling. These alterations could be correlated with environmental perturbants, such as use of radiant warmers or surface skin occlusion.
The Adaptation Process
We have investigated the adaptation process among 100 healthy newborns under standard clinical conditions during the first few hours of life. We used noninvasive biophysical techniques to evaluate hydration status, transepidermal water movement, surface water binding, surface acidity, and surface texture.
Comparison of the chest and back skin among one cohort showed a higher rate of water movement through the stratum corneum, a more acidic surface and lower surface desquamation. We speculate that the rate of change in stratum corneum-water properties is delayed for the back because it is not directly exposed to the warmer. In a second group, the skin of the lower abdomen was protected with an occlusive bag. The protected skin demonstrated a slower rate of stratum corneum drying than the exposed site. Additionally, we observed that rapid desorption of surface water was associated with a dry surface. The facility for rapid water desorption, such as the presence of a hydrophobic surface, conveys a survival advantage for protection against evaporative heat loss and perhaps against colonization with microorganisms.
Research Implications
These results have implications for optimizing infant skin care beginning at birth. They provide the scientific basis for standardization of clinical practices. Studies are currently underway to determine the effect of the stratum corneum water interactions and environmental factors on the skin status of the infant over time. We are also investigating the microenvironment of the infant stratum corneum and mechanisms for modifying it in order to prolong and maintain the optimum, skin state for a longer period after birth. We anticipate identification of mechanisms to minimize the negative effects of various environmental influences.
