LIPSTICK
Lipsticks first appeared in the ancient city of Ur, near Babylon, 5,000 years age. Egyptians made lipsticks from finely crushed carmine beetles, which yielded a deep red pigment, mixed with ant eggs as a base. Eliza- bethan lipsticks were a blend of cochineal and beeswax. For many centuries, lip reddeners consisted of a very poisonous substance called mercuric sulfide. Lipsticks in their modern form were introduced after World War I; they were colored with a dye and acid-base indicator (carmine) chemically extracted from the small red cochineal insect (Coccus cacti). Indelible long-lasting lipsticks were introduced in the 1920s and became colored upon reacting with the skin. It is this technology of the 1920s on which modern color-change lipstick chemistry is based.
Modern lipstick is formulated to provide both protection for the deli- cate tissues of the labia and color for appearance. The chemical composi- tion of lipstick varies greatly among manufacturers. However, lipstick in general is formulated to provide uniform color coverage while being neutral in taste, stable under normal fluctuations of temperature, mois- ture, and air flow, and lacking toxicity and irritancy. Lipstick should re- main relatively stiff and intact within the dispenser tube but flow easily onto the lips under application pressure. To achieve these goals, the spe- cific chemical composition may include a mixture of oils, waxes, pig- ments, emollients, antioxidants, and preservatives. Perfumes are often added to mask the unpleasant fatty odor of the oil. Much of the body mass of the lipstick is composed of a mixture of a nonvolatile oil (e.g., castor, vegetable, mineral, or lanolin) and solid wax (e.g., beeswax or carnauba). The addition of oil allows the wax-based product to be soft- ened and easily applied. In addition, esters of fatty acids (e.g., 2-propyl myristate) are commonly added to reduce any “stickiness.”
Many consumers view the color of lipstick as the most important char- acteristic of this product. The colors and dyes of lipsticks are generally regulated within the United States and include many water-insoluble (oil- soluble) products, such as brilliant blue, erythrosine, amaranth, rhodamine, tartrazine, dibromofluorescein, and tetrabromofluorescein (bluish-red com- pound). The dyes must be water insoluble; otherwise, the color would quickly fade or be removed in a short time by the consumer through the movement of the saliva-soaked tongue across the lips. Water-soluble dyes such as green or blue food dyes may be used to provide lipstick colora- tion, but they are usually first “laked” or combined with metal oxides such as aluminum hydroxide [Al(OH3)] to form an insoluble precipitate that is then suspended in the oil base of the lipstick.
Eosin is a commonly used pigment that yields an intense red color upon application after chemical reaction with numerous -NH2 (amine)- containing skin surface proteins. For some color-change lipsticks, the lightly colored eosin pigment is masked in the applicator tube by a laked green or blue dye. Thus, the laked dye is the color viewed before the lip- stick is applied, and the color change when the lipstick is applied to the lips is intense as eosin yields a red color. These types of lipsticks fre- quently contain acids (e.g., citric or lactic), as the color-change dyes tend not to function properly under basic conditions.
The very popular “mood lipsticks” are composed of weak acid color pigments that have a conjugate base form with a remarkably different color. Thus, these lipsticks are simple acid/base indicators. When the lip- stick reacts with the skin, it changes to a color varying according to the pH of the skin at the time of application. Since the pH of the skin is de- pendent on numerous physiological factors (e.g., physical activity level, stress, nutrition, hormonal fluctuations) and genetically different natural base skin colors, the color of the mood lipstick varies from application to application.
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