The TEWL (Transepidermal Water Loss) Test is a laboratory method used to evaluate the integrity and performance of the skin barrier. It measures the rate at which water naturally evaporates from the skin surface, offering an accurate indication of skin barrier health and hydration efficiency. This test is essential for assessing the effects of cosmetic products such as creams, serums, cleansers, and barrier repair formulations.

Purpose of the TEWL Test

The TEWL test helps determine whether a cosmetic product strengthens, maintains, or disrupts the skin’s protective barrier. It provides valuable insight into product performance, particularly for formulations claiming to reduce dryness, improve hydration, or protect against environmental damage.

How the Test Works

The TEWL measurement is performed using an Apparatus Test, typically with a specialized device such as an open-chamber or closed-chamber evaporimeter. The apparatus measures the water vapor flux from the skin surface under controlled temperature and humidity conditions. The results are expressed in grams of water per square meter per hour (g/m²h), representing the rate of water loss through the epidermis.

Applications in Cosmetic Testing

• Evaluation of moisturizing or hydrating formulations
• Assessment of barrier-repairing or protective creams
• Validation of claims related to “moisture retention” or “barrier function improvement”
• Testing of products for sensitive or damaged skin
• Comparative studies before and after product application

Test Procedure

1. Volunteers are acclimatized to a controlled environment (temperature and humidity).
2. Baseline TEWL values are recorded on untreated skin.
3. The test product is applied according to the intended use conditions.
4. TEWL values are measured again after defined intervals (e.g., 30 minutes, 2 hours, 24 hours).
5. Data are analyzed to determine the impact of the product on the skin barrier.

Results & Reporting

The final report includes:

• Detailed description of test conditions and apparatus used
• Mean TEWL values before and after product application
• Statistical analysis of observed differences
• Interpretation of barrier function performance
• Graphical representation of results (optional)

Why TEWL Testing Matters

The skin barrier plays a vital role in maintaining moisture balance and protecting against irritants. A compromised barrier leads to dryness, redness, and sensitivity. TEWL measurements provide objective data that confirm whether your product effectively supports barrier recovery and hydration — key factors for product validation and marketing claims.

Sample Requirements

• Minimum quantity: 11 finished products
• Product type: any topical formulation (cream, lotion, serum, cleanser, ointment)
• Storage conditions: room temperature unless otherwise specified

Typical Turnaround Time

Results are typically available within 10–15 working days from the date of sample receipt and protocol approval.

Deliverables

• Full laboratory report in PDF format
• Summary of results suitable for regulatory or marketing documentation
• Optional inclusion of data in claim substantiation reports

Compliance & Standards

The test follows guidelines consistent with international cosmetic testing standards and ISO 15197 laboratory quality procedures. All studies are conducted under controlled environmental conditions to ensure accuracy and reproducibility.

Related Tests

• Corneometry (Skin Hydration Test)
• Sebumeter (Skin Lipid Measurement)
• pH Measurement of Skin Surface
• Clinical Evaluation of Barrier Repair Products