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AquaFlux Questions >  Answer 9

AquaFlux Answer 9

Are there any published Guidelines for TEWL measurement, and how do they apply to the AquaFlux ?

The quick answer is yes and no. Yes, much of what they recommend is valid for all measurement methods. No, they were written for open-chamber instruments and the AquaFlux is different. If you want the long answer, read on.

There are two published guidelines for TEWL measurement in general [1, 2], and one for TEWL measurement in non-clinical settings [3]. Guidelines [1, 2] consider open-chamber instruments only. Guidelines [3] consider both open-chamber and unventillated-chamber instruments. But none of these publications included any AquaFlux measurements.

Guidelines [1, 2] discuss (a) person-linked variables, (b) environmental variables and (c) instrumental variables in some depth before presenting their recommendations for best practice. Most of the considerations of sections (a) and (b) are valid for all methods of measurement. The exceptions are section (a) of [2], where the discussion of skin surface temperature includes consideration of how this may affect the measurement probe, and section (b) of both both publications, which include discussions of air circulation and how this may cause fluctuations in open-chamber measurements. Neither of these are concerns for the AquaFlux. Section (c) and elsewhere is instrument-specific and not applicable to the AquaFlux.

The table below presents a side-by side comparison of the recommendations of these guidelines with what we recommend for the AquaFlux.

Guideline Citations

Ambient Temperature & Humidity
If climate room facilities are available, the ambient room temperature should be regulated to 20-22°C and the relative humidity to 40%. Individuals should rest for 15-30 minutes before TEWL measurements [1].

Usually it is suggested to keep the temperature between 20 and 22±1°C and the relative humidity lower than 60%. Acclimatize for at least 15-30 minutes [2].

These recommendations are valid for all TEWL measurement methods. They define the conditions necessary for skin acclimatisation, to avoid sweat gland activity and skin surface moisture. You cannot take the bio out of bioengineering.

In addition, we recommend the use of a fan to expedite the drying of skin surface water, especially at the higher end of the ambient RH range.

Ambient Air Movements - Shielding Box
Perform all TEWL measurements within a large "open-top" box whenever possible [1].

Measurements should be carried out in a room with limited air circulation. A shielding box with an open top can be used if doubt exists whether undesirable air turbulence is present or not [2].
Ambient air movements have no effect on AquaFlux measurements.
Post-measurement Recovery
Avoid using the "offset" button in between measurements for zeroing and allow it to "zero" on its own, before the next measurement is made. (2-4 minutes post-measurement) [1].

An equilibrium time should be taken into consideration before the next measurement is started. The process can be accelerated by moving the probe [2].
No recovery time is necessary before starting the next measurement, because of the controlled microclimate. You can move from site to site without any delay.
Holding the Probe
Do not hold the probe directly by hand. The probe should be handled with an insulating glove, or the calibration rubber stopper supplied with the equipment, or a burette clamp [1].

The measuring probe itself should not be touched before and during measurements and can be handled with the electrical wire, a coating or by wearing gloves [2].
There are no measurable effects from hand heat while holding the AquaFlux probe.
Contact Pressure
The contact pressure of the probe onto the skin should be kept low and constant [1].

... with a constant but light pressure. Measurements within one experiment should preferably be performed by the same operator [2].
No measurable contact pressure effect has been found. This appears to be an open-chamber design deficiency rather than a skin property.
Probe Angle
The measuring surface should be placed in a horizontal plane, and the probe applied parallel to this surface [1].

The measuring surface should be placed in a horizontal plane and the probe should be applied perpendicularly to this surface [2].
You can measure with any surface orientation. You need to hold the probe correctly to limit sensitivity changes with probe angle to ±1%.

[1] J Pinnagoda, RA Tupker, J Agner and J Serup. Guidelines for Transepidermal Water Loss (TEWL) Measurement. A Report from the Standardization Group of the European Society of Contact Dermatitis. Contact Dermatitis. 22, 164-78: 1990.

[2] V Rogiers and the EEMCO Group. EEMCO Guidance for the Assessment of Transepidermal Water Loss in Cosmetic Sciences. Skin Pharmacol Appl Skin Physiol. 14,

[3] J du Plessis, A Stefaniak, F Eloff, S John, T Agner, T-C Chou, R Nixon, M Steiner, A Franken, I Kudla & L Holness. International Guidelines for the In-vivo Assessment of Skin Properties in Non-clinical Settings: Part 2. Transepidermal Water Loss and Skin Hydration. 19(3), 265-78: 2013.

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