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Answers to Top 3 Skin Performance Testing Questions

Dermatology TimesDermatology Times, February 2024 (Vol. 45. No. 02)
Volume 45
Issue 02

In this month’s Cosmetic Conundrums column, explore skin barrier assessments, skin moisturization tests, and how to measure skin firmness.



The cleanser and moisturizer market is crowded and performance-driven. Consumers demand skin care products that smell good, feel good, leave the skin feeling soft, and enhance skin performance. How does the manufacturer determine which pilot formulation is the best to finalize for distribution? How can skin care companies be sure new products meet consumer expectations and result in a repeat purchase? Consumers will purchase a product once based on packaging claims, confidence in a given brand, and appearance, but they will not always make a second purchase.

The best way to determine which products did not succeed is to look at the clearance aisle in the store. Skin care retailers know exactly how many sales of a given product must occur on a daily basis to justify the shelf space. If the profit on 4 inches of shelf space is not sufficient, the retailer will replace the product with one that performs better. Stores do not sell products; they sell shelf space.

Thus, skin care manufacturers must develop a finely tuned testing methodology through which new products and revised formulations must pass. This article examines what these tests are and how they guide the cosmetic chemist in selecting products for optimal dermatology performance.

Q: How can product effects on the skin barrier be assessed accurately?

The skin barrier is the stratum corneum consisting of the protein-rich corneocytes surrounded by the intercellular lipids. Barrier effect analysis is particularly important in cleanser formulations where the surfactants remove surface lipid-soluble dirt but are nonspecific and can easily remove the intercellular lipids. If the intercellular lipids are removed, the amount of water loss from the skin surface (known as transepidermal water loss [TEWL]) will increase and the skin will become dehydrated. TEWL is measured by placing a known diameter collecting tube on the skin containing 2 humidity meters at a known distance above the skin. The measurement of water vapor leaving the skin is determined by the humidity meters, allowing a determination of the amount of water lost per unit area per unit time (gm/cm2/hour).

A good cleanser will not increase TEWL, thus a variety of formulations can be tested on humans to determine which induces the least barrier damage. Ten prototype formulations can be reduced to the top 3 performers using TEWL, and these 3 products can then be put into the clinic for testing. TEWL is an excellent predictor of product barrier effects, but clinical validation is still necessary.

Q: How can you test for skin moisturization?

TEWL is an excellent measure of the water leaving the skin, but it is also necessary to understand how much water is present in the skin. Good moisturizers will immediately increase the skin water content upon application, with continued increases noted with continued use. Although consumers mainly judge a moisturizer on how smooth and soft it makes the skin feel, an increase in skin hydration must occur over time or the consumer will find the product ineffective.

Corneometry is a technique used to measure skin water content by utilizing the fact that water is a conductor of electricity. Higher corneometry readings correlate with an increased skin water content. The technique does not work if the skin surface is wet from immediate product application, as the product will short circuit the corneometer and measure the hydration of the skin surface and not the skin itself.

Q: How do you scientifically measure skin firmness?

Testing is also necessary to substantiate claims on skin care product packaging. Facial moisturizers like to claim that use improves the skin’s firmness. What is skin firmness? I am not sure. This is the perfect cosmetic term because it means something quite scientific to the consumer, but to the dermatologist, it is a term defying definition. From a mechanistic standpoint, skin firmness refers to the amount of force it takes to pull the skin with a negative suction vacuum pump. Firmer skin requires more force to produce skin distention. To improve skin firmness, increase the water content of the skin with a moisturizer.

Zoe Diana Draelos, MD, is a consulting professor of dermatology at Duke University School of Medicine in Durham, North Carolina, and Dermatology Times' Editor in Chief Emeritus.

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