58 TESTING


Figure 4: TEWL measurements for all kinds of applications.


Assessing nails and eyes Up until now, there are not that many measurement methods that are used for the assessment of nails. Studies have revealed that healthy nails have a much higher water loss than one would expect, being higher than the TEWL of the skin and behaving differently.9,10 Also, an age-dependency could be shown.11 Therefore, TOWL measurement will hint at


nail health and can be used to demonstrate the effect of hand and nail care and products such as nail polish or polish remover. Leaving the skin altogether, another field of


application is the measurement of the water loss from the eye surface. With a healthy and stable tear film, ocular water loss is limited. For people with dry eye symptoms, an increased water loss can be measured using a modified TEWL probe.12


Ocular water loss could be an


interesting parameter to study the impact of products used on the eye such as contact lenses or the creeping effect of products applied close to the eye.


In vitro TEWL Last but not least, TEWL measurements play an increasing role in the field of in vitro studies on cultured tissue. The use of skin tissue models for long-


term safety tests is a quick and easy method to avoid using animals or volunteers and allow economic pre-tests to see the efficacy of products. Meanwhile in vitro tests have been well established in various guidelines around the globe.13 Besides using a probe in a special shape to fit on the Franz cell’s membrane, there are systems available to measure TEWL in a well plate with up to 24 cultured tissue wells simultaneously. The acquired data have many uses in this field. From the initial check of the


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quality of cell cultures, the assertion of constant test conditions outside the incubator as the TEWL threshold avoids too dry/too moist conditions for product application, up to the barrier function effect of applied products, the TEWL measurement is indispensable for safety & efficacy assessments because even small effects are detectable and the measurement helps to separate experimental stress effect by the condition inside and outside the incubator from tested product’s effect.


Conclusion No wonder that a multi-informational parameter as the Transepidermal Water Loss is indispensable for all kind of cosmetic, pharmaceutical and medical applications and beyond.


References 1 Berardesca E, Loden M, Serup J, Masson P,


Rodrigues LM. The revised EEMCO guidance for the in vivo measurement of water in the


skin, Skin Res Technol. 2018;24:351–358 2 Information video on the Tewameter® (youtube): https://youtu.be/wlwJstCwFfU


TM Hex


3 Basal metabolic rate, Wikipedia https://en.wikipedia.org/wiki/Basal_metabolic_ rate


4 Braun N, Binder S, Grosch H et al. Current Data on Effects of Long-Term Missions on the International Space Station on Skin Physiological Parameters, Skin Pharmacol Physiol 2019; 32:43-51


5 Agren J, Sjörs G, Sedin G. Ambient Humidity Influences the Rate of Skin Barrier Maturation in Extremely Preterm Infants, J Pediatr. 2006;148(5):613-617.


PC


6 Yonezawa K, Haruna M, Matsuzaki M, Shiraishi M, Kojima R. Effects of moisturizing skincare on skin barrier function and the prevention of skin problems in 3-month-old infants: A randomized controlled trial, Journal of Dermatology 2018; 45: 24–30.


7 Vazquez-Gonzalez ML, Rodriguez G, Rubio L, et al. Intelligent ageing repair with skin superfoods, Personal Care Europe 2019; 157- 162.


8 Khazaka D, Uhl C. Nails: more than just skin extensions, Personal Care Asia Pacific 2018; 33- 35


9 Krönauer C, Gfesser M, Ring J, Abeck D. Transonychial water loss in healthy and diseased nails, Acta Derm Venereol. 2001;81(3):175-177.


10 Jemec GB, Agner T, Serup J, Transonychial water loss: relation to sex, age and nail-plate thickness. Br J Dermatol. 1989;121(4):443-446.


11 Jeon HS, Youn SW, Jeon HE, Kim JH, Hyon JY. Assessment of Transepidermal Water Loss From the Ocular Area in Dry Eye Disease, IOVS 2016; 57: 11; 4835


Figure 5: Assessing TEWL in 24 cultured tissue wells simultaneously.


12 European Centre for the Validation of Alternative Methods (ECVAM) guidelines: https://ec.europa.eu/jrc/en/eurl/ecvam


September 2020


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