Introduction

The chemical industry designs and produces a vast number of chemical products to serve the society. Chemical products are classified as molecular products, formulated products, functional products, and devices.1,2 Among them, formulated products such as cosmetic and paint are formed by mixing selected ingredients in a formula, which may possess certain microstructures of their own (e.g., powder and emulsion). The formula (i.e., ingredient selection and composition) has a significant impact on formulated product quality. Thus, the major aim of formulated product design is to find a formula that exhibits consumer-desired properties.2,3
As a major component of formulated products, cosmetics are applied to the human body for cleansing, beautifying, promoting attractiveness, or altering appearance. They are sold in many forms. Table 1 lists the commonly used cosmetic product forms such as cream and gel. The global cosmetic market valued at $532 billion in 2017 is large, but competitive and dynamic.4 Many cosmetic products exist on the market but they tend to have short product life. To succeed in this environment, rapid formulation of new and improved cosmetics is crucial. The quality of cosmetics can be broadly represented by two types of attributes. One is sensorial attributes (e.g., smell and sight) perceived by five human senses during and after the application of cosmetics. The other is functional attributes (e.g., stability and safety), which ensures that cosmetics can be assuredly used with the desired functions. Table 2 lists the relevant sensorial and functional attributes of four cosmetic products with different product forms. For instance, the senses of how lipstick is felt by the lips and how the lips look after application are part of the lipstick quality. Meanwhile, lipsticks should be stable, safe, and not broken in use. It is known that the sensorial quality is the dominant consideration for consumers to choose one cosmetic product over another.5,6 Thus, it needs to be explicitly considered in cosmetic formulation.