Trans Epidermal Water Loss (TEWL) is the ratio of vapor passing from the skin layers to the environment. This value is the absolute indicator of skin barrier function and skin integrity. Normal TEWL is 4-8 g/m2/h for an effective stratum corneum barrier. Higher values indicate that the barrier is damaged, not well constructed, contains less than the normal 16 barriers. TEWL studies based on age support the perspective of newborn skin barrier functions.