A new approach to evaluate temporal changes in sensation when applying cosmetics

When evaluating the quality of a cosmetic product, people focus on several properties at the same time. One of the most important properties, apart from the moisturizing and other skincare effects, is the tactile sensation when the product blends onto the skin. In a typical product-testing setting, the tactile sensation of a cosmetic applied to the skin, such as "smooth" and "good hold to skin", is usually evaluated after application. So far there have been no detailed evaluations of the changes in sensation a person experiences moment by moment while a cosmetic is being applied.

Kao Corporation has developed a new evaluation method to enable sensory panelists to report how the sensations change moment by moment while cosmetics are being applied using an eye-tracking interface. This method is based on the Temporal Dominance of Sensations (TDS), a method used to record the dynamic process of sensations that evolve over time while tasting foods or drinks.
TDS measurements begin immediately after a product is placed in the mouth of a sensory panelist. The panelist notes changes in sensation second by second by pressing the keys of a keyboard to choose the most dominant sensory attributes -"sweet," "bitter," and the like- displayed on a computer screen. The changes in the chosen ratios of each attribute are then plotted out visually as a linear graph or TDS curve after measurements with some more panelists.
A challenge arises when adapting the TDS to an evaluation of tactile sensations of cosmetics. If the panelist chooses the dominant attributes by pressing a keyboard, the fingertip sensations are likely to interfere with motion of applying cosmetics and the sensory perception of the cosmetic product. By adopting an eye-tracking computer interface in place of a keyboard, the fingers are freed from all sensory distraction during the TDS evaluation. To choose an attribute such as "smooth" or "good hold to skin," the panelist simply directs their eyes to the attribute on the computer screen (Fig. 1). Attribute choice with an eye-tracking interface also eliminates the delays experienced with keyboard and oral selection, allowing the panelist to concentrate more completely on the sensations themselves and perform the evaluation in real time. The trials so far performed have confirmed that an eye-tracking interface is well suited for the evaluation of second-by-second changes in sensation.
The words used to describe the sensory attributes are also important. The descriptors for the current study were selected from a list of words expressing tactile sensations perceived during application of the cosmetics (current targets described below). The selected attributes are based on the factor structure of this list and effectively describe attributes that change with the passing of time.

Changes in sensation experienced moment by moment during the application of a cream-type test formula and a milky-lotion-type test formula were evaluated for six attributes selected using the above-described method (Fig. 2). The outstanding attributes of the cream-based formula were "smooth" in the first stage, followed by a sense of "good hold to skin" that was maintained from a relatively early stage until the end of application. The outstanding attributes in the evaluation of the milky-lotion-based formula were "smooth" in the first stage, followed by "smooth," "oily," and "good hold to skin". The latter was also the most prominent sensation from the middle stage until the end. This method made it possible to evaluate the changes in sensation experienced moment by moment while the cosmetics were applied. Relatively high reproducibility with the same panelist was also confirmed.

Kao intends to use this method for the design and assessment of cosmetics with the aim of developing products that provide a high sense of value and pleasing sensations when applied to the skin.

Kao creates high-value-added products that enrich the lives of consumers around the world. Through its portfolio of over 20 leading brands such as Attack, Bioré, Goldwell, Jergens, John Frieda, Kanebo, Laurier, Merries and Molton Brown, Kao is part of the everyday lives of people in Asia, Oceania, North America and Europe. Combined with its chemical division, which contributes to a wide range of industries, Kao generates about 1,500 billion yen in annual sales. Kao employs about 33,000 people worldwide and has 130 years of history in innovation. Please visit the Kao Group website for updated information.