Skin health_rate of water loss

There are many methods to detect the skin health, skin surface properties, skin color, skin color type, and hair conditions. They are non-intrusive.

Skin health
l   Rate of water loss
Use a device to evaluate TEWL (trans-epidermal water loss). This measurement can be representative of stratum corneum function if there is no sweat on the skin. 
TEWL(trans-epidermal water loss) is an index to define the hydration of skin.
Unit: g/ m2h

The device could be closed-chamber method, ventilated-chamber method, and open-chamber method. TEWL measurement follow diffusion laws, and the TEWL results would depend on the ambient relative humidity, the stratum corneum barrier integrity, the temperature, and inversely on the stratum corneum thickness.
closed-chamber method
This method is applied a capsule on the skin to collect water vapor from skin surface. The relative humidity inside is record first. The change in vapor loss concentration is initially flat and decrease proportionally as the humidity reaches 100%. This method cannot record continuous TEWL. The reason is the skin evaporation cease as the air inside is saturated.  

ventilated-chamber method
This method is a gas of known water content will pick up water as it passes through is applied on the skin. The measurement will be recorded through a hygrometer. This method allows the continuous measurement of TEWL, but if the carrier gas is too dry, it artificially increases evaporation

open-chamber method
This method is the capsule open to the atmosphere. TEWL is calculated from the slope provided by two hygrosensors precisely. Air movement and humidity will influence the measurement. 

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