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.