(a) Cooling. The heat flux caused by the low condenser temperature (conduction through the air & radiation) is too small to cause the skin surface temperature to change significantly. We went to some lengths to try to measure an effect, using highly sensitive thermocouples and superglue (PhD thesis, Don O'Driscoll, London South Bank University, 2001). The main finding was that skin cooling was dominated by conduction between the skin and the measurement head and any effect from the condenser was masked by this. No effect on measured TEWL values was found.

(b) Drying. There is a measurable effect from prolonged contact with a condenser-chamber measurement head, as described in the poster presented at the SCIII Conference in Basel (Ciortea et al, 2002). The main finding was that the TEWL decreased at a rate of ~0.1% per minute of contact. Given that a TEWL measurement requires typically 1 minute of skin contact, the effect on accuracy is small.

The above work was performed using an AquaFlux AF100 instrument, with a condenser chamber temperature of -13.4C. The effect is likely to be less with the AF200 because (i) the condenser temperature is higher at -7.6C and (ii) the waisted measurement chamber. Both cause the microclimate RH at the skin surface to increase for a given TEWL, and therefore reduce the drying effect on the SC.