Development of stratum corneum chymotrypsin-like protease activity and natural moisturising factors from birth to 4 weeks of age compared to adults.

BACKGROUND: From birth, the functional properties of the neonatal epidermal barrier mature whereby the stratum corneum (SC) hydrates and the skin surface acidifies. The identification of a thinner infant SC compared to adults suggests underdeveloped mechanisms underlying differentiation and desquamation. OBJECTIVES: To assess the functional properties of the neonatal SC from birth, in conjunction with the quantification of superficial chymotrypsin-like protease activity (kallikrein-7 [KLK-7]) and filaggrin-derived natural moisturising factors (NMF). METHODS: A total of 115 neonates recruited to the oil in baby skincare (OBSeRvE) randomised controlled trial underwent a full evaluation of the SC at birth (<72 hours old) and at 4 weeks of age (n=39, no oil control group) using minimally invasive instrumentation and methodology. A cohort of 20 unrelated adults was recruited for comparison. RESULTS: At birth NMF levels correlated with SC hydration (r=0.50) and skin-surface pH (r=-0.54). From birth to 4 weeks, transepidermal water loss (TEWL), superficial KLK-7 activity and filaggrin-derived NMF significantly elevated. Impaired epidermal barrier function at birth (>75th percentile TEWL) was accompanied by significantly elevated chymotrypsin-like protease activity and reduced levels of NMF. CONCLUSIONS: The biophysical, biological and functional properties of the developing neonatal SC are transitional from birth to 4 weeks of age and differ significantly to adults. The presence of impaired barrier function with elevated protease activity and reduced NMF at birth suggests why certain infants are predisposed to epidermal barrier breakdown and the development of atopic dermatitis (AD). This article is protected by copyright. All rights reserved.