Lipstick is one of the most commonly used cosmetic products – and a range of chemicals are required for its production. The choice of these ingredients is carefully considered to provide the desired colour, glossiness, and indelibility. A single stick of lipstick will contain several hundred different chemical compounds, but there are a few substances and compounds whose inclusion is essential.
An average composition of lipsticks is given in the graphic, but, in truth, this can be widely varied from lipstick to lipstick. Generally, however, waxes and oils make up the bulk of lipstick’s composition. Waxes are perhaps the most important, as they are crucial for the structure and shape of the lipstick. A range of different naturally occurring waxes can be utilised, with beeswax commonly a major constituent. Beeswax is composed of around 300 different chemical compounds; the principal compounds are esters, which make up around 70% of the composition. The remaining 30% of compounds include organic acids and hydrocarbons.
Another type of wax used is Carnauba wax, obtained from the Brazilian Carnauba Palm, which at approximately 87˚C has the highest known melting point of any wax. Its inclusion can give the lipstick the rather useful characteristic of not melting in the sun as a result of the lower melting points of some of the other waxes used. As well as beeswax, these other waxes can include Candelilla wax, obtained from the Mexican Candelilla shrub, and lanolin, a wax secreted by the glands of woollen animals. Though they primarily provide the structure of the lipstick, these waxes can also impart other useful properties – they can act as emulsifying agents to help bind together the other ingredients, and can also impart glossiness on the application of the lipstick.
As well as the waxes, another important component of lipsticks is oils. The most commonly used is castor oil, which can often comprise the largest percentage of the lipstick, but others, such as olive oil and mineral can also be utilised. The oils give the lipstick emollient or skin-softening properties; they also make the application of the lipstick easier and contribute glossiness to its appearance. Additionally, they act as solvents for soluble dyes used in the lipstick, or dispersing agents for any insoluble pigments.
The pigments and dyes, though they make up only a minor percentage of the lipstick’s composition, are certainly the most important, as they impart the colour of the lipstick. Pigments are coloured compounds that are insoluble, whilst dyes are more commonly either liquids themselves, or soluble. The manner in which they provide colour can also vary. Carmine red, also known as carminic acid, is a common red pigment, which is derived from cochineal bugs, a variety of scale insects that live on cacti. It is prepared by boiling the insect bodies in ammonia or sodium carbonate solution, filtering, and then adding hydrated potassium aluminium sulfate (more commonly known as alum).
Another common colour-imparting component is a compound called eosin. This is a dye that actually subtly changes its colour when applied. In the lipstick, it is red, with a slightly blue tinge; when it is applied, however, it reacts with the amine groups found in proteins in the skin, and this reaction causes its colour to intensify to become a deeper red. Another benefit of this reaction is that it makes the dye indelible, or long-lasting.
Of course, red is not the only lipstick colour, and in order to achieve the wide range of colours available today, other pigments and dyes are needed, of which there is a variety. Additionally, other compounds can be added in order to alter the intensity of the red-coloured pigments and dyes. Titanium dioxide, a white compound in isolation, is a common addition, which can be added to red dyes in varying amounts to produce a range of pink-coloured lipsticks.
Several other compounds can be added in small quantities to provide moisturising qualities, or to provide a pleasant fragrance that also masks the smells of the other compounds that make up the lipstick. Interestingly, capsaicin, the major capsaicinoid compound in chillis which is largely responsible for spiciness, can also sometimes be found in lipsticks. Its presence is down to its ability to act as a minor skin irritant, which means it can cause lips to appear plumper.
On a final note, in recent years there has been concern over the very small amounts of heavy metals that can be found in some lipsticks. A recent study of 32 popular lipsticks found trace contaminant amounts of lead, cadmium, aluminium, chromium and manganese in many of them. However, this study has come in for criticism in some quarters, as it based its human ingestion estimates on a range of different data for each metal, and also assessed the amounts ingested with the assumption that all of the applied lipstick was ingested – an unlikely scenario. Additionally, the highest levels of the metals in the study were still below the recommended daily intake. The presence of heavy metals in lipsticks is still a legitimate concern, however, particularly with no safe level of exposure to lead being recognised, and as such there is a push for a limit of specific levels of the metals in lipstick to be set. In the meantime, many companies now produce lead-free lipsticks to assuage consumer fears.
References & Further Reading
- Waxes used in cosmetics – Making Cosmetics
- What’s in Lipstick? – C&EN
- Indelible Lipsticks – Cosmetics & Skin
- The cosmetic chemistry behind lipsticks – Beauty & the Geeks
- Vanity, Vitality & Virility – The Science Behind the Products You Love to Buy – John Emsley
- Analysis of Lipsticks by Surface Enhanced Raman Scattering – C Rodger & others