The relationship between skin maturation and electrical skin impedance.

When performing electrophysiological testing, high electrical impedance values are sometimes found in neonates. Since excessive impedance can invalidate test results, a study was conducted to delineate the relationship between skin maturation and electrical skin impedance. This study investigated the skin impedance in 72 infants ranging from 196 to 640 days of age from conception. Regression analyses demonstrated a significant relationship between impedance and age, with the highest impedance centered around full-term gestation with values falling precipitously at time points on either side. Clinically, impedance values fall to normal levels at approximately four months following full-term gestation. Skin impedance values are low in premature infants, but rapidly increase as the age approaches that of full-term neonates. Low impedance values in premature infants are attributed to greater skin hydration which results from immature skin conditions such as 1) thinner epidermal layers particularly at the transitional and cornified layers; 2) more blood flow to the skin; and 3) higher percentage of water composition. These factors facilitate the diffusion of water vapor through the skin. As the physical barrier to skin water loss matures with gestational age, the skin impedance reaches a maximum value at full term neonatal age. After this peak, a statistically significant inverse relationship exists between electrical skin impedance and age in the first year of life. This drop in skin impedance is attributed to an increase in skin hydration as a result of the greater functional maturity of eccrine sweat glands.