Transepidermal Water Loss (TEWL)
The measurement of water evaporating from the skin surface, used as an indicator of skin barrier function. Higher TEWL indicates compromised barrier integrity. Some peptide-based skincare products are evaluated for their ability to reduce TEWL and improve skin barrier function.
Technical Context
TEWL is measured using evaporimeters (open-chamber — Tewameter; closed-chamber — VapoMeter; or unventilated-chamber systems) that detect water vapour flux from the skin surface. Normal TEWL values: forearm approximately 5-10 g/m²/h, face approximately 10-15 g/m²/h. Elevated TEWL indicates barrier disruption (atopic dermatitis: 15-25 g/m²/h; severely damaged skin: >25 g/m²/h). TEWL is used as: a diagnostic measure of skin barrier function, an endpoint in barrier repair studies, a quality control metric for skincare product efficacy, and a research tool for evaluating peptide formulation effects on skin integrity. For transdermal peptide delivery research, TEWL measurement confirms whether delivery technologies (microneedles, iontophoresis) have created transient barrier disruption sufficient for peptide penetration without causing excessive or prolonged skin damage.