By Eunice Lam 林杏妍
If office ladies are asked to put only one cosmetic product on their faces, many of them will choose to have lipstick as it drastically increases the redness of their lips, making them appear more vibrant. To produce a high-quality lipstick, a variety of chemicals are specifically chosen in the formulation to achieve the desired texture and color.
Beeswax and cocoa butter are two of the most commonly used ingredients in lipsticks that together make up the bulk of the product. Lipsticks need to be soft enough to slide over our lips but stiff enough to stay intact during their application. A group of scientists investigated the effect of varying the proportions of these ingredients: they found that hardness depended upon the amount of beeswax and spreadability depended upon that of cocoa butter . Thus, having the right ratio of these two ingredients will give the perfect lipstick.
The secret behind this “golden ratio” lies in the chemistry of these two major substances. Beeswax is largely consisted of saturated esters 1, such as triacontanyl palmitate (Figure 1). In this beeswax ester, both components feature long and saturated hydrocarbon chains (a C30 alcohol 2 & a C16 acid). Cocoa butter, on the other hand, is mostly made up of triglyceride 3 (fat) molecules. A common triglyceride in cocoa butter (Figure 2) features palmitic acid (C16, saturated); stearic acid (C18, saturated) and oleic acid (C18, monounsaturated).
The hardness of these substances at room temperature is linked to their melting points. Melting point is the temperature at which the molecules have sufficient kinetic energy to break free from the intermolecular forces holding them together as a solid. The strength of the intermolecular forces in this case, lies within the molecules’ ability to pack tightly: since the closer they can get, the stronger the attractive forces they could then exert onto each other.
In the cocoa butter triglyceride, the presence of oleic acid’s cis-double bond in one of three “arms” can disrupt molecular packing with a rigid “kink”. You may imagine this as the troublesome irregular block in the Tetris game. Whereas the saturated chains of the beeswax ester molecules allow them to pack tightly together in a regular manner, thus giving a harder structure.
In mixtures, a sharp melting point is not observed, but they tend to gradually soften and melt over a temperature range. The correct mix of beeswax and cocoa butter is a complex mixture that would be in a partially molten state at room temperature, making it just soft enough and neither rock hard nor a puddle.
Figure 1. Triacontanyl palmitate
Figure 2. A common triglyceride of cocoa butter
Color is another important characteristic of lipsticks. Back when synthetic dyes were not yet known, people could only look to nature for the colors they desired. The major red pigment used back then (and nowadays!) was carmine (also called cochineal, carminic acid, E120 and CI 75470). This blood red dye is extracted in a literally bloody process, by grinding the dried female cochineal insect, Dactylopius coccus, which live as parasites on cacti . I believe it may scare many of you that what you are applying onto your lips were made from crushed insect bodies. Besides, although carmine is widely used in cosmetics, it has been known to cause allergic reactions in a very small number of people . Luckily, there are also carmine-free products available in the market for vegans and people who are allergic to it.
A more recent pigment used in lipsticks is eosin, which creates a long-lasting sharp red color only after application because it reacts with amine groups (NH2) present on skin surface proteins .
Color-changing lipsticks are recently in fashion and they rely on color-changing chemistry. Some of them employ color masking, in which an originally light-colored dye (such as eosin) would be initially masked by a darker pigment so the lipsticks do not appear red at first. Some may use humidity to trigger a color change too: for example a colorless dye, Red 27, turns pink after reacting with moisture on the lips. Another popular variation, known as “mood lipstick”, uses pH-sensitive dyes. As the pH of the lips could vary due to different physiological conditions (e.g. stress, hormonal fluctuation), a “personalized” red color would appear on the lips .
Apart from organic colorants, inorganic compounds are also used. Iron (III) oxide (Fe2O3) is often added to lipsticks – the hydrated form of which (Fe2O3·xH2O) is rust as we commonly know it. Commercial colorants’ shade can be tuned by controlling synthesis procedures, giving for example, iron oxides with a wide range of colors. The use of iron oxide colorants is a much safer and environmentally-friendlier choice than many organic dyes.
Understanding what is inside a lipstick is very important as a smart consumer. Next time when you buy a new lipstick, remember to check the labels first!
1 An ester (RCOOR’) is a condensation product (meaning that H2O is lost during the coupling reaction) between an alcohol (OH) functional group and a carboxylic acid (COOH) functional group.
2 C30 alcohol refers to the alcohol that has a carbon chain (or known as carbon backbone) with 30 carbon atoms.
3 A triglyceride molecule is also an ester, but here the alcohol component is glycerol, a triol with three OH groups on a C3 skeleton; thus three carboxylic acid components will condense with it form a triester.
 Kasparaviciene, G., Savickas, A., Kalveniene, Z., Velziene, S., Kubiliene, L., & Bernatoniene, J. (2016). Evaluation of Beeswax Influence on Physical Properties of Lipstick Using Instrumental and Sensory Methods. Evidence-Based Complementary and Alternative Medicine, 2016. doi:10.1155/2016/3816460
 Pöhnl, H. (2016). Applications of Different Curing Approaches and Natural Colorants in Meat Products. In Carle, R., & Schweiggert, R. M. (Eds). Handbook on Natural Pigments in Food and Beverages – Industrial Applications for Improving Food Color (pp. 209-225). Elsevier.
 Arslan, Z. K., & Aycan. Ş. (2014). An Example of the Use of Spectrophotometric Method: Determining the Carmine in Various Food Products. Procedia – Social and Behavioral Sciences, 116, 4622-4625. doi: 10.1016/j.sbspro.2014.01.996
 Toedt, J., Koza, D., & Cleef-Toedt, K. V. (2005). Chemical Composition of Everyday Products. Westport, CT: Greenwood Press. Retrieved June 12, 2019, from https://books.google.com.hk/books?id=UnjD4aBm9ZcC&lpg=PA44&dq=lipstick eosine&hl=zh-TW&pg=PA43#v=snippet&q=beeswax lipstick&f=false