Trans Epidermal Water Loss (TEWL) is a measure of the quantity of water that evaporates from the skin and passes into the surrounding environment. It is an essential indicator of the skin’s barrier function, and thus plays a critical role in cosmetic product development for several reasons:
1. Product Efficacy:
One of the key ways to determine the effectiveness of a cosmetic product, especially those designed to hydrate the skin, protect skin barrier function, or provide anti-aging benefits, is to measure its impact on TEWL. If a product can demonstrably reduce TEWL, it is likely to be more effective in moisturizing the skin and maintaining or restoring the skin’s barrier function.
2. Product Claims Substantiation:
Being able to scientifically prove that a product reduces TEWL can form the basis for marketing claims. For example, a brand could claim that its product “reduces moisture loss” or “strengthens the skin’s barrier function”. These kinds of claims are particularly appealing to consumers who understand the importance of the skin’s barrier function for overall skin health.
3. Safety and Tolerability Assessment:
Increased TEWL is often a sign of skin irritation or damage. Thus, measuring TEWL can be an important part of safety and tolerability testing for new cosmetic products. If a product increases TEWL, it could be irritating or damaging to the skin and may need to be reformulated.
4. Formulation Development:
Understanding the impact of various ingredients on TEWL can guide the formulation process. For example, occlusive agents (like waxes or oils) can help reduce TEWL by forming a physical barrier on the skin, while humectants (like glycerin or hyaluronic acid) can help reduce TEWL by attracting and holding water in the skin.
5. Innovation:
Knowledge of TEWL and the skin’s barrier function can drive innovation in cosmetic product development. This can lead to the creation of new products or formulas that more effectively reduce TEWL, or the discovery of new ingredients that have beneficial effects on the skin’s barrier function.
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Understanding and controlling TEWL is critical for the development of effective and safe cosmetic products. It allows developers to create products that truly meet the needs of the skin, providing moisturizing, protective, and anti-aging benefits, and to make marketing claims that are supported by solid scientific evidence.
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