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Epidermal barrier development is essential for transition to a terrestrial environment after birth. In addition to water impermeability and a plasticized biomechanical interface, the skin surface in adults exhibits an acidic pH(4.5-5.5). This “acid mantle” is considered to be important for infection control and barrier lipid organization. Although the precise cellular and molecular mechanisms underlying acid mantle development in humans are unknown, there appear to be striking similarities with the developing lung and the acidification of the alveolar surfactant hypophase. This study was designed to provide baseline data for exploration of acid mantle development in infants. Skin surface pH was determined over the chest of 102 term newborn infants using a flat surface pH electrode (Courage & Khazaka, model 900). Data are reported as mean ± sem. Significance was assumed whenever p<0.05.

Results: A decrease in skin surface pH was observed over the first week of life. At 2 h postpartum, the mean pH was 7.0 ± 0.1 and 6.6 ± 0.1 by 16 h. By day of life 7, the pH had declined to 5.4± 0.1. The decrease in pH was statistically significant at all time points. The effect of topical surfactants (Dial™ or Safeguard™) was examined in some infants (N=29) 20 minutes after the first bath. Bathing induced a significant increase in pH from 7.0 ± 0.1 to 7.4 ± 0.1. Site specific differences were also observed. The forehead at 4h of age under the radiant warmer showed a significantly lower surface pH compared to the chest accompanied by a decreased surface temperature.

Conclusions: 1) The skin surface of the term infant is acid neutral at birth; 2) acid mantle development is initiated within the first 16 hours of age; 3) standard bathing practices alkalinize the skin transiently followed by rapid reprotonation; 4) regional differences in skin surface pH may be accompanied by shifts in surface temperature. We speculate that study of the human infant after birth offers a unique opportunity to study the mechanism of epidermal protonation and acid mantle development.

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Rone, J., Bare, D., Pickens, W. et al. ACID MANTLE DEVELOPMENT IN THE NEWBORN INFANT. † 1020. Pediatr Res 41, 172 (1997).

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