How to Know if a Product Actually Repairs the Barrier
In our barrier repair studies, C.R.E.A.M. 2.0 outperformed all of the products tested which comes as no surprise because this is what it was painstakingly designed to do.
We knew we wanted to improve on the barrier repair ability of our original C.R.E.A.M., so we kept formulating, updating, and testing until it surpassed all others in terms of barrier repair.
The short and quick answer is testing.
Whether we are working on a new product or just a product update, testing is one of the most fundamental steps in our R&D process here at Regimen Lab. We go beyond the typical consumer survey where products are given subjective scores as to whether or not they improve skin feel or overall look. In our barrier repair studies, C.R.E.A.M. 2.0 outperformed all of the products tested which comes as no surprise because this is what it was painstakingly designed to do. We knew we wanted to improve on the barrier repair ability of our original C.R.E.A.M., so we kept formulating, updating, and testing until it surpassed all others in terms of barrier repair.
When it comes to barrier repair products, measurement of trans-epidermal water loss (TEWL) is the widely accepted method to determine effects on barrier function and repair in a non-invasive manner. This is also the method that we use when we set out to assess our products for TEWL-reduction or barrier repair abilities. We specifically follow the experimental protocols from the lab of Dr. Peter Elias and EMMCO Group guidance. By outlining our methodology, we are making the testing we do replicable by anyone with access to the knowledge and equipment to do so. We also realize that despite the rigor of our methods, as a consumer, you still have to trust that these results are accurate.
What device is used?
We use the Tewameter TM Hex by Courage and Khazaka, an upgrade to the gold-standard Tewameter TM 300. A tewameter is an instrument that measures the moisture your skin normally loses (aka TEWL), which is correlated to your barrier health. The device we specifically use has an open-chamber equipped with 30 sensors inside the probe to account for relative humidity and temperature. This allows for continuous TEWL measurements without affecting the skin’s microenvironment while simultaneously compensating for the effects of humidity and temperature for highly accurate measurements.
What is the test location?
Measurements are performed on the volar forearm as this allows for multiple products to be tested simultaneously. TEWL values vary across anatomical sites on the body and are influenced by factors such as sweat glands and skin thickness. The palm and sole have some of the highest TEWL rates on the body. Although it would be more suitable to evaluate products on facial skin, this would require multiple testing periods and results amongst the groups could not be directly compared.
How is the barrier damaged?
The skin is tape-stripped using d-squame stripping discs until it reaches a TEWL of 30-40 g/h/m2. There are two alternate barrier damage techniques which are also used in literature studies (acetone and SLS), but tape stripping provides more consistent results between test sites and the desired TEWL can easily be achieved. In order to artificially damage the barrier via tape stripping, the adhesive side of a d-squame stripping disc is pressed down onto the skin using a D-squame Pressure Instrument for 5 seconds and subsequently removed. Every disc that is applied removes a layer of the skin and, thus, increases the TEWL value. It usually takes about 50 d-squames to reach 30 g/h/m2.
When are measurements taken?
The first measurement that is taken is prior to any barrier damage occurring. This establishes a baseline for the skin’s normal TEWL value. A second measurement is taken immediately after barrier damage (T = 0), so that the reduction of TEWL can be monitored. TEWL is then measured at various time points following product application (T = 2, 4, 6, 8, 24 hours). For each test site and time point, the continuous TEWL measurement is taken until the value for Spread is below 0.5 and the Uncertainty value is below 1. All measurements using the Tewameter are performed by the same operator to ensure that the device is placed on the skin with the same pressure for each test site.
How is barrier repair ability calculated?
Barrier repair ability is obtained using the formula from Mao-Qiang (1996):
This formula is an application of the Normalization Formula, where we want to find out what percent does a value have in between a maximum and a minimum. In this case, minimum refers to the basal TEWL of the skin before any damage while maximim refers to the TEWL after tape stripping (30-40 g/h/m2.)
How many test subjects are there?
In our studies the group size is 6 (n = 6). It is ensured that all test subjects are within the same age group and do not have any known or visible skin conditions that could affect TEWL values. Prior to any measurements, all test subjects are acclimatized to the climate-controlled environment for 1 hour and do not apply any other products that day.
How much product is applied?
To maintain consistency between products, 10 mg of each product is weighed out for application to a marked 3.14 cm2 area. Prior to the study, a Scientist not involved in testing blinds the samples by assigning a random numerical code to each one which corresponds to the test site.
What is the reference material?
Petrolatum and a barrier lipid-free product (La Roche-Posay Cicaplast Baume B5 Soothing Repairing Balm) are used as reference materials. This helps reduce differences related to instrumentation. A negative control site is also included where the skin is tape-stripped but no product is applied. This allows for a direct comparison of a product’s ability to accelerate barrier repair through TEWL reduction.
- Sample Size: Most tape stripping literature studies use 6 to 10 human volunteers. Although n = 6 is a sufficient number of volunteers for an adequate statistical analysis, a larger sample size would increase the power and reliability of the study. With a larger sample size, significant differences could potentially be seen amongst the top performing products.
- Barrier Damage: The only method that was employed to damage the barrier was tape-stripping. This method physically damages the skin barrier by removing layers of skin down to the Stratum Granulosum. Products’ ability to accelerate barrier repair following chemical insult (i.e. barrier damage via acetone and SLS) was not explored in this study.
- Product Application: The area of application, amount of product, and rub times are all controlled among test sites. However, there are products which contain encapsulated ingredients which may require more rubbing time to release the barrier repair actives. This could have an effect on the product’s results for barrier repair ability.
- Sensitivity: Despite the many controls put in place, there are a number of factors that could also affect TEWL values. Since the Tewameter TM Hex is an extremely sensitive instrument, factors such as sleep, sweat, caffeine, wind, and movement could affect readings and overall barrier repair abilities. The EMMCO guidelines also recommend that in addition to age, the sex and race of the test subjects should also be considered and remain homogenous.
Courage+Khazaka electronic GmbH (n.d.). Tewameter® TM Hex. Courage+Khazaka electronic GmbH. https://www.courage-khazaka.de/en/?view=article&id=257&catid=16
Mao-Qiang, M. (1995). Exogenous nonphysiologic vs physiologic lipids. Archives of Dermatology, 131(7), 809. https://doi.org/10.1001/archderm.1995.01690190063012
Mao-Qiang, M., Feingold, K. R., Thornfeldt, C. R., & Elias, P. M. (1996). Optimization of Physiological Lipid Mixtures for Barrier Repair. Journal of Investigative Dermatology, 106 (5), 1096–1101. https://doi.org/10.1111/1523-1747.ep12340135
Mao-Qiang, M., Feingold, K. R., Wang, F., Thornfeldt, C. R., & Elias, P. M. (1996). A Natural Lipid Mixture Improves Barrier Function and Hydration in Human Skin. Journal of the Society of Cosmetic Chemists, 47, 157-166.
Rogiers, V., & EMMCO Group (2001). EMMCO Guidance for the Assessment of Trans Epidermal Water Loss in Cosmetic Sciences. Skin Pharmacology and Applied Skin Physiology, 14 (2), 117-128. doi: 10.1159/000056341.
Yang, L., Mao‐Qiang, M., Taljebini, M., Elias, P. M., & Feingold, K. R. (1995). Topical Stratum Corneum Lipids Accelerate Barrier Repair After Tape Stripping, Solvent Treatment and Some But Not All Types of Detergent Treatment. British Journal of Dermatology, 133 (5), 679–685. https://doi.org/10.1111/j.1365-2133.1995.tb02738.x
Zetterson, E. M., Ghadially, R., Feingold, K. R., Crumrine, D., & Elias, P. M. (1997). Optimal Ratio of Topical Stratum Corneum Lipids Improve Barrier Recovery in Chronologically Aged Skin. Journal of the American Academy of Dermatology, 37 (3), 403-408. https://doi.org/10.1016/S0190-9622(97)70140-3