Sensory Spectrum

ABSTRACT

This chapter provides the reader with an objective use of the Senses and Sensory Evaluation to describe perceivable behavior in the world of personal care and cosmetic products. Sensory perception is at once fundamental and ambiguous. Each of us uses our senses to understand the world around us through vision, touch, hearing, smell, and taste. Through interpretation of those sensations by our brains, we name what we perceive, and those naming labels are influenced by our background and training. Through organized, objective understanding of product features, standardized attributes can be developed and applied for testing and decision-making.

TABLE OF CONTENTS

7.1.1 Overview

7.1.2 History of sensory evaluation

7.1.3 Defining sensory properties

7.1.4 Rationale for generating technical-based language for objective product description

7.1.5 Introduction to descriptive analysis methodology

7.1.6 The spectrum descriptive analysis method: philosophy and principles

7.1.7 Fundamentals for developing lexicons

7.1.8 Process for developing personal care product lexicons

7.1.9 Sample lexicon and testing protocol for lotions and creams

7.1.10 Sample protocol for skin preparation and maintenance during testing

7.1.11 Sample lexicon and testing protocol for evaluation of hair tresses

7.1.12 Sample lexicon and testing protocol for evaluation of lather and skinfeel of bar soaps

7.1.13 Sample lexicon and testing protocol for evaluation of appearance and skinfeel of antiperspirants using inner arm site

7.1.14 Sample lexicon and testing protocol for evaluation of appearance and skinfeel of facial foundation using half-face

7.1.15 Applications of descriptive analysis for personal care and cosmetics

References

7.1.1 OVERVIEW

The field of Sensory Evaluation has evolved as a tool to understand and organize our perceptions. It is a scientific discipline that addresses methods to evoke, measure, analyze, and interpret human responses to properties of materials perceived through our five senses. While there is valuable basic research into how the brain interprets sensory input, the most common purpose of sensory evaluation is to conduct valid and reliable tests that provide data for decision-making. This is especially important in the development of cosmetic and personal care products whose purpose is to enhance the perception of “beauty.”

Measurement of Sensory perception is an ambiguous science due, in large part, to differences in the way we express what we perceive as opposed to the differences in what we perceive (although those differences exist as well). When working with others, our individual interpretations and previous experiences may lead to our describing different sensations with the same word or to describing the same sensation with different words. This issue often causes confusion and miscommunication. The situation is all too common when describing personal care products. Researchers and marketers in the personal care and cosmetic industries have expressed frustration with this lack of uniformity since it often leads to inefficiency in development, marketing, and testing. On the positive side, sensory evaluation testing, thoughtfully done, can measure subjective consumer perceptions to products through their liking of and preferences for products. It can also provide a focus on objective measurement of important product features that are useful in further product development, product maintenance, and the generation of claims for such products.

Even with the growing use of sensory evaluation within personal care product and ingredient companies, its applications are weighted towards product assessment based on liking as well as preference by the target consumers, the client, or the decision-makers within a company. This chapter provides an introduction to objective sensory evaluation. It describes methodology for documenting the sensory properties of personal care products through use of a technical-based language called Descriptive Analysis currently in use by many in industry, academia, and consulting.

The approach to effective objective sensory evaluation is provided through use of lexicons (representative and comprehensive lists of words to describe a product or category) and protocols, methods use for assessment, as well as leveraging other sciences such as chemistry, rheology, and physiology. This system provides a harmonized framework for understanding product attributes as well as evaluation of objective techniques to characterize appearance, texture, and fragrance across a wide range of products. Examples include commercial formulations, model systems, and raw ingredients that are applied to the skin, body, and hair.

While this chapter is an introduction to this methodology, it does not replace a full descriptive analysis training; rather, it provides examples of an objective language for describing sensory perception as related to personal care products and allows users to have an improved ability to communicate with one another. It describes the process of lexicon development, provides sample lexicons for several large product categories, and demonstrates the underlying commonalities across disparate product categories. The conclusion of the chapter provides several applications of objective descriptive analysis for decision-making within companies.

7.1.2 HISTORY OF SENSORY EVALUATION

Use of our senses for learning and decision-making has existed throughout history. People categorize products as good or bad, more or less, acceptable or not acceptable, and they learn to assign intensity judgments to these categories as well as product features.

This basic use of the senses for measuring and judging was refined as trading, buying, and selling flourished. Portions of lots were viewed or sampled in order to set prices and determine quality of foods and other goods. The process of product grading continues to this day worldwide. By the early 1900s, measurement of product sensory properties extended with the addition of the professional taster and consultant (Meilgaard et al. 2007). The field grew for measurement of sensory properties in foods as well as for measurement of consumer subjective ratings for acceptance of food products, such as that conducted by the U.S. Army Quartermaster Food & Container Institute to measure food acceptance for the U.S. Armed Forces (Peryam et al. 1954).

By the late 1950s and 1960s, more scientific rigor in terms of assessor selection, testing conditions, testing procedures, and statistical analysis began to be employed at the university and industry levels (Pangborn 1964; Caul 1957; Szczesniak 1963). The Food Science Department at the University of California at Davis was one organization that advanced the field, resulting in the foundational book Principles of Sensory Evaluation of Food (Amerine, Pangborn, and Roessler 1965).

While sensory evaluation, or organoleptic testing (Pfenninger 1979), was initially focused within the field of consumer food products, it has increasingly been applied to personal care, home care, paper, and fabric products. Organoleptic testing was an attempt toward objective testing of products. As the field has continued to develop formalized methodology/practices for effective consumer testing relative to acceptance and preference and for objective testing for discrimination and measurement of product attributes, the term has fallen out of favor.

The first publication cited for objective sensory evaluation of personal care products was Schwartz, 1975, with Adaptation of the Sensory Texture Profile Method to Skin Care Products, based on the Texture Profile Method developed by General Foods in the 1960s (Szczesniak 1963). Sensory Spectrum applied and expanded this methodology through the Spectrum Descriptive Analysis method in the 1980s and published two research papers on descriptive analysis techniques. One of these was for skin care products (Civille and Dus 1991) and the other for paper/fabric (Civille and Dus 1990).

A number of discrete sensory methodologies for evaluation of personal care products are in current use, with some practitioners blending methodologies. Regardless of methodology, the working sensory professional is tasked with acquisition and interpretation of valid data. Erhardt (1978) specifies seven tasks for sensory research:

• • determine the project objective
  
• • determine the test objective
  
• • screen the samples
  
• • design the test
  
• • conduct the test
  
• • analyze the data
  
• • interpret and report results.

Sensory Evaluation methods, research, practices, and applications are documented in journals including, but not limited to those such as Chemical Senses, Journal of Sensory Studies, Journal of Texture Studies, Food Quality and Preference, Journal of Food Science, Food Technology, Cosmetic & Toiletries, and Journal of Cosmetic Science.

Conferences on the subjects include: Sensometrics (biannual), Pangborn Sensory Science Symposium (biannual), Society of Sensory Professionals (biannual), and Eurosense (biannual). These conferences are associated with professional organizations. Selected standards and guides are published by ASTM Committee E18 (www.astm.org) and the International Organization for Standardization (IS0) (www.iso.org). A growing number of independent companies and consultancies are devoted to sensory evaluation services, with some providing training courses, and several textbook stylebooks on sensory evaluation are widely available. While the majority of resources are focused on foods and beverages, sensory evaluation resources specific to “nonfoods” continue to grow rapidly.

7.1.3 DEFINING SENSORY PROPERTIES

Sensory properties are defined as the characteristics perceived through the senses; not the liking or preference for products. These properties exist, regardless of whether we like them or not, regardless of whether we’re even aware of some of them. They are what a product looks like, smells like, tastes like, feels like, and sounds like. They can also demonstrate what a substrate, such as the skin or hair is like, and how the interaction with a product changes that substrate during and after product use.

Meilgaard et al. (2007) provide an extensive list of references for study of the human senses and the properties measured by them.

High-level categories for sensory properties are described as follows:

• • Appearance:

Characteristics measured by the sense of vision to include optical and physical characteristics.

• • Aroma/Olfaction:

Volatiles perceived by the olfactory system through the nose or oral cavity. The biology of the nose and its sensing ability are extensively covered elsewhere in this book.

• • Flavor:

The complex, integrated effect of basic taste sensations (the perception of properties perceived through the taste buds), olfactory sensations, and chemical feeling factors/trigeminal nerve (the fifth cranial nerve) sensations stimulated by a substance in the mouth.

• • Texture:

The way something feels when touched or eaten, based on its surface and/or the way it changes when compressed or manipulated, to include geometrical, moisture, mechanical, and noise-based properties.

• • Sound:

Noise characteristics measured by the sense of hearing during mastication or manipulation of products.

While all senses can come into play when measuring the sensory properties of personal care products and ingredients, those properties most commonly measured are appearance, texture, and, particularly for finished goods, aroma. Products designed for use in or on the mouth, such as oral care products and lip products, are often evaluated for flavor.

7.1.4 RATIONALE FOR GENERATING TECHNICAL-BASED LANGUAGE IN ORDER TO OBTAIN OBJECTIVE PRODUCT DESCRIPTIONS

Objective description of product attributes can be expressed through technical-based language rooted in other scientific disciplines such as rheology, chemistry, and physiology. Use of a technical-based language has several advantages for developers and researchers over consumer language–based descriptions.

Consumers are very good at describing what they do and do not like. They are less adept in providing detailed reasoning for their opinions. Typical consumer-based describing language tends to

• • Categorize perceptions into good/bad
  
• • Compare to other familiar (to the consumer) products, without context
  
• • Include emotions
  
• • Be vague or inconsistent
  
• • Include attribute terms that are integrated, having multiple technical components (e.g., creamy, slimy, gummy)

Conversely, technical-based language is designed to

• • Consider terms as neutral descriptors, not as being positive or negative
  
• • Identify and define physical- or chemical-based terms
  
• • Use fundamental, single-meaning terms rather than multifaceted, integrated terms

Technical-based language can be used to “break open” perceptions that are difficult for consumers to articulate, or have multiple facets, such as “soft,” “refreshing,” or “creamy.” Generation and understanding of an objective language for describing product attributes has the following benefits (Stapleton 2013):

• • Places the focus on product properties and design features, rather than individual evaluator or decision-maker preferences for products
  
• • Simplifies intra-company communication across business units and locations so that all parties understand attribute terms in the same way
  
• • Streamlines development and research due to better feedback and direction
  
• • In many cases, correlates to instrumental testing

Certainly, consumer liking and preference are of critical importance to the success of products in the marketplace. Consumer descriptions of products garnered from questionnaires, reviews, interviews, and other sources have value for marketers, developers, and sensory personnel since they provide an understanding of what consumers value, despite its often-imprecise nature. The adept researcher develops skills to translate the “fuzzy” world of consumer responses into objective parameters that can be measured and manipulated to create consumer-preferred products. Understanding products from an objective standpoint enhances the ability of the researcher to make those connections to ask consumers questions in ways that yield more useful detail.

7.1.5 INTRODUCTION TO DESCRIPTIVE ANALYSIS METHODOLOGY

Descriptive analysis is a tool that provides detailed documentation of product properties and allows more objective comparison of products for enhanced decision-making. Descriptive analysis records the applicable sensory characteristics of a product in terms of the attributes perceived and the strength of each attribute.

Descriptive analysis methods involve the detection and the description of both the qualitative (attribute terms) and quantitative (intensity of signal) features of a product by trained panels of judges prescreened for acuity in the categories of interest and absence of preexisting conditions or health issues for the panel of interest (ASTM STP758 1981).

Panelists may be recruited internally or externally through agencies, advertising, word of mouth, and more recently through social media, which to an accelerating degree in the rapidly evolving use of the Internet, is supplanting more traditional newspaper advertising. The number of judges is based on the level of training and risk level of the decisions made by the panel and varies between 5 and 25. Training involves introduction and practice in the terminology, evaluation protocols, and scaling for product evaluation. Scaling techniques involve the use of numbers, distance, or words to express the intensity of a perceived attribute across differing products (Meilgaard et al. 2007).

Choice of a scaling system is dictated by the precision needed in measuring differences, the amount of training the panel receives, the selection of a specific descriptive analysis method and its recommended scale, and the historical use of objective sensory data within a company. Scales should have the ability to discriminate small differences. Post hoc, line, and numerical intensity scales can be transformed to other scale systems. Category data such as counting how many times a motion occurs or assigning yes/no presence to a perception does not need to be transformed. For analysis, scales must be converted to numerical values.

The SpectrumTM Descriptive Analysis Method (Civille) uses technical-based language for terminology and grounds itself in the use of published and internal intensity reference scales to define intensity boundaries in sensory experiences. This method is utilized globally by a variety of finished product, cosmetic, and ingredient personal care companies. Other descriptive analysis methods are in use for evaluation of personal care products reflecting differences in training philosophy and data collection assumptions. Moreover, companies often blend methodologies to create internal, customized sensory testing programs. In this chapter, the SpectrumTM Descriptive Analysis Method serves as an exemplar of a successful modality to achieve our analytical goals.

7.1.6 THE SPECTRUM TM DESCRIPTIVE ANALYSIS METHOD: PHILOSOPHY AND PRINCIPLES

The SpectrumTM Descriptive Analysis Method for personal care products trains professionals with the goal of generating panelists that function similarly to a calibrated instrument. Panelists are screened and selected on their ability to detect and discriminate differences in appearance and tactile qualities. Fragrance evaluation can be trained within the same or a different panel; again, panelists must screen and pass screening for acuity. Panelists are trained on a universal scale that focuses on intensity or strength of the signal coupled with detailed description and definitions of sensory attributes and use of calibrated training samples. In this method, panelists are trained for visual and tactile evaluations and receive a minimum of 100 hours of training and practice prior to commissioning for sensory studies. Their training is provided across a diverse set of products within a broad category such as lotions, creams, and gels.

Attribute intensity is rated on a 100-point intensity scale, with 0 = none and 100 = very strong/very high. The intensity scale uses 1-point increments. Alternatively, a 0 to 10 scale using 0.1 increments can be employed. Panelists are trained to use the scale in a similar way across panelists and across samples. Data are collected from the individual judges with replication of sample presentation recommended. Analysis is designed for correlation with both instrumental and consumer research data. Use of a universal scale allows attribute intensity to be compared across various parameters, e.g., comparing intensity of slippery feel to intensity of sticky feel, as well as for comparison of samples within and across studies and products having shared attributes. The panel is monitored for accuracy and performance with ongoing conformance assessments. For further detail and for historical foundations of the SpectrumTM Descriptive Analysis Method, see Meilgaard et al. (2007). Project-specific orientation is provided to a working panel as needed. Following initial training, panelists are often trained in additional product categories as appropriate to the end user. Subsequent training follows the same universal scaling construct such that panelists always interpret the scale intensities in a similar way; for example, a value of 47 on a 100-point scale represents a moderate intensity for any attribute.

When training a new panel, the group may generate its own terminology based on close and repeated examination of a range of products following the guidelines for development of technical-based language, or it may rely on established terminology such as presented here. In either case, this process includes using references to clearly demonstrate each term so it is understood in the same way by all panelists. The scope of terms may be broad or focused according to the panel’s purpose and the test objective. Repeated exposure and practice, along with ongoing availability of reference standards, allows attribute understanding to be internalized and provides ongoing intensity calibration similar to that used for an instrument.

While a traditional SpectrumTM panel requires approximately 100 hours of training and practice with the terminology and scaling system before being capable of performing within expected tolerances for repeatability, reliability, and accuracy, the initial process of learning terminology, qualitative references, and protocol techniques can be introduced in a matter of ten hours or less. Companies often benefit from having their developers and marketers understand technical/descriptive language around a product category in order to focus internal product assessment on objective descriptions rather than personal liking and preferences. In such cases, these oriented persons are not intended to function as a statistically valid panel. With some additional practice beyond the initial orientation, companies sometimes use a subset of these persons to screen samples and gather initial information on competitive products.

7.1.7 FUNDAMENTALS FOR DEVELOPING LEXICONS

Lexicons are systematically created descriptor lists to objectively characterize the sensory properties of consumer products. They allow differing parties to communicate efficiently when describing products of interest (Lawless and Civille 2013).

While hundreds of lexicons exist in the literature, it is the responsibility of the user to assess the quality of any lexicon considered for use. ASTM International (www.astm.org) prescribes five steps for development of a well-designed lexicon, based on use of an established panel and valid protocol evaluation techniques (ASTM Stock #DS72 2011):

1. 1) Select a large number of products representative of the category breadth to establish a “frame of reference”
   
2. 2) Generate terms that describe the products
   
3. 3) Use references that clarify the terms and definitions
   
4. 4) Use examples so that the panel understands the attribute terms well
   
5. 5) Develop the final list of lexicon terms

During selection of the final list of lexicon terms, attributes should be reviewed to ensure they are nonredundant and not correlated with one another (Civille and Lawless 1986). The lexicon is validated by using it to compare a small subset of products in the category as confirmation that it will describe and discriminate between the products. In addition to providing terms, definitions, and examples, lexicons should provide specific instructions for the way the attributes should be assessed (Meilgaard et al. 2007). Lexicons developed using these principles are well designed and can be successfully used by multiple panels or trained groups to describe products. They are created for use with a scaling system so that intensity differences between similar products can be differentiated. However, lexicons can be applied to multiple scaling systems and often do not include scale intensity information apart from indicating the directionality of the scale.

All lexicons presented in this chapter were developed using the principles above. These lexicons provide a strong foundation to those developing their own lexicons and for those interested in understanding product attributes.

Figure 1: provides a synopsis for developing a product lexicon.

7.1.8 Process for DEVELOPING PERSONAL CARE PRODUCT LEXICONS

Personal care products exist in many forms ranging from lotions to shampoo, to facial scrubs to color cosmetics and antiperspirants—just to name a few categories. It is a common misconception that each product or product category is defined by a unique set of words. In truth, many attribute descriptors, for example those related to visual and tactile texture, are common to many forms. Once one learns the terminology for one product category, many of those same attributes exist in other categories. In part, this is due to the characterization of the underlying rheological characteristics (i.e., how the product’s viscosity at different shear rates and measurement times changes when dispensed, deformed, and manipulated) in the context of their use within the world of personal/skin care as well as for foods and fabrics. Table 1 demonstrates the rheological manifestations of three mechanical force related attributes across foods, personal care products, and fabrics.

Table 1: Comparison of Three Mechanical Properties across Foods, Skincare, and Fabric

What differentiates the lexicons for various products categories are the applicable terms chosen for each. For example, shampoo, facial cleanser, and bar soap all generate foam, though each may have bubbles of different size, variation, density, and amount. None of those attributes apply to nonfoaming products such as lotions, foot creams, and facial serums. In turn, part of what differentiates lexicons for related products such as the foaming ones described above are the test substrate selected (hair tress, cheek, and arm, respectively) and the protocol instructions for assessment. A detailed description of the various substrates are described elsewhere in this book. This description entails not only the physicality of the substrate but the chemistry, biology, and molecular genetic characteristics.

From the author’s personal experience, the learned understanding of the “universal” nature of attributes across product types is mind expanding. Of note was the realization that grittiness (small, abrasive particles) for sandpaper, paper towels, razor stubble, and the flesh of pears during chewing all manifested in a similar sensory signal although the substrates and matrices differed. Noticing the commonalities among disparate product types reinforces the fundamental concept of quantitative sensory perception technology that a given attribute can exist in multiple products, albeit at varying intensities or prominence. With practice, one can learn to focus on the sensory attributes that characterize a product rather than the product’s brand image, reputation, or typical nature or on the evaluator’s personal degree of liking for any facet of the product.

Training Process

In learning how to describe visual and tactile properties of personal care products, an efficient introductory category is the broad lotion category that includes lotions, creams, and gels. It is efficient for training for a number of reasons:

• • Wide array of products are available
  
• ○ Broad Range of Intensities Across Attributes
  
• • Provides a substantive product laydown, allowing residues to be perceived and named
  
• • Is a familiar product form
  
• • Is generally easy to remove using isopropyl alcohol or mild cleansers
  
• • Has a form similar to other product categories such as:
  
• ○ Suncare
  
• ○ Shampoo/Conditioner
  
• ○ Liquid Soap/Body Wash
  
• ○ Foundation/Primer/Serum
  
• ○ Topical Pharmaceuticals (OTC and Ethical)
  
• ○ Certain Liquid-Form Ingredients

Attributes are introduced within the framework of a testing protocol. The protocol provides a set of procedural directions for conducting an evaluation. A thorough protocol provides instructions for the session leader and participants regarding room conditions, test site preparation, and product presentation in addition to the techniques used to assess the attributes. A well-written protocol allows trained evaluators to evaluate product in the same way, using the same techniques and under similar conditions, yielding results that can be directly compared to one another.

Attributes are introduced and learned individually. However, product assessment is a continuous process that includes the following phases:

• • Application to the test substrate
  
• • Product manipulation on the test substrate (extent of manipulation varies)
  
• • Feel of product on test substrate post–product manipulation (one or more time points)

Product assessment can also involve the following:

• • Visual evaluation of product during or after dispensing
  
• • Tactile manipulation of the neat product without spreading

Role of References

In training, each attribute is demonstrated using one or more references. A reference can be a product applied to the test site following the technique used for assessment, such as a measured amount of cream on a defined area of skin rubbed a defined number of times, or it can be demonstrated using the native test site itself, such as a hair tress/switch or volar forearm skin. A reference may be qualitative, meaning it is clear or dominant in the attribute, or can be quantitative, meaning it possesses a scaled intensity amount of the attribute. When quantitative references are used, it is recommended that three or more levels are demonstrated. A reference allows association of a physical (or visual or chemical, as applicable) signal with the attribute so that the attribute perception can be discussed and understood. Discussion within the group is important, so that participants can recognize where their personal vocabularies are consistent and inconsistent with the attribute explanation demonstrated, and the focus can be placed on the sensory attribute, not on personal feelings about the attribute characteristics.

Table 2 demonstrates quantitative reference scales for two attributes—wetness and product thickness.

Table 2: Example of Skinfeel Attribute Intensity Reference Scales (0 to 100 point)

7.1.9 SAMPLE LEXICON AND TESTING PROTOCOL FOR LOTIONS AND CREAMS

In the following section, products are dispensed by the panel leader or technician. Panelists record requested information for each attribute on a corresponding ballot for that lexicon and protocol.

Qualitative references provided demonstrate a moderately high to high intensity of the attribute.

Appearance and Feel of Lotions and Creams

Product Appearance (Appearance of Dispensed Product)

In a polystyrene petri dish, panel leader uses a standardized orifice container to dispense the product in a spiral shape using a 2-cm circle, filling it from the edge to the center.

Evaluate for:

Integrity of Shape Degree product holds shape

[flattens ———————————– retains shape]

Qualitative Reference Petrolatum, white

Integrity of Shape Degree product holds shape

(10 seconds) [flattens ———————————– retains shape]

Qualitative Reference Petrolatum, white

Tilt petri dish to see reflective properties and evaluate for:

Gloss Amount of reflected light from product

[dull/flat ———————————– shiny/glossy]

Qualitative Reference Baby oil or light mineral oil

Additional appearance attributes can be measured, including the following:

Color Hue The actual color name or hue, such as red, blue, etc. The description can be expressed in the form of a scale range, if the product covers more than one hue.

Color Intensity The intensity or strength of the color from light to dark:

[Light ———————————– Dark]

Color Purity The chroma (or brightness) of the color, ranging from dull, muddied to pure, bright color. Neon green is brighter than olive green.

[Dull ———————————– Bright]

Product Pickup (Manipulation of Dispensed Product for Rheological Properties)

Using automatic pipette or syringe, panel leader delivers 0.1 cc of product to tip of thumb or index finger. Compress product slowly between index finger and thumb one time, then separate fingers. Evaluate for:

Firmness Force required to fully compress product between thumb and index finger

[no force ——————————— high force]

Qualitative Reference Petrolatum, white

Stickiness Force required to separate fingertips

[no force/ not sticky ———————– high force/very sticky]

Qualitative Reference Petrolatum, white

Using the same dispensed product or wiping product from fingers and receiving another dose, compress and separate product between the index finger and thumb three times using a quick, light pressure, and evaluate for:

Cohesiveness Amount sample strings rather than breaks when fingers are separated

[no strings ——————————– high strings]

Qualitative Reference Petrolatum, white

Amount of Peaking Degree to which product makes stiff peaks on fingertips

[flat/no peaks———————————– stiff peaks]

Qualitative Reference Petrolatum, white

Rub-out (Product Application and Manipulation)

Using automatic pipette or syringe, panel leader delivers 0.05 cc of product to center of 5-cm diameter circle on volar forearm. Spread the measured amount of product within the circle using index or middle finger, using a gentle circular motion. Stroke at a rate of two strokes per second, following a metronome.

After three rubs, evaluate for:

Wetness Amount of water perceived while rubbing

[none ————————————- high amount]

Qualitative Reference Water

Spreadability Ease of moving product over the skin

[difficult/drag —————————- easy/slip]

Qualitative Reference Baby oil or light mineral oil

After 10–15 rubs, evaluate for:

Thickness Amount of product felt between fingertip and skin.

[thin/ ————————————— thick/]

Related posts:

– EMERGING STRATEGIES FOR SUSTAINABLE PACKAGING: BALANCING MATERIALS, DESIGN, AND APPEARANCE – MULTI-FUNCTIONAL BOTANICALS FOR NUTRICOSMETICS APPLICATIONS – METHODS TO ASSESS SKIN BARRIER INTEGRITY: EFFECTS OF CLEANSING PRODUCTS – SUSTAINABILITY & ECO-RESPONSIBILITY – FORMULATING COSMETICS AND PERSONAL CARE PRODUCTS – IMAGING TECHNIQUES AND ANALYSIS FOR QUANTIFICATION OF SKIN APPEARANCE

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