Chemistry of Makeup

One of the residual facts that has stuck in my head from my geology degree is that mica (a type of mineral) is used in make up highlighters to give that shimmery shine. I mentioned this fact in passing to someone I was tutoring the other day and we ended up getting into a convo about the chemistry behind make up, and its actually quite fascinating. For something that really is part of my everyday life, I didn't know much about the chemicals that went into it - and sadly I fear this is true for quite a lot of the things in my life. So after some research I thought I would share my findings on here in case anyone else is interested in what it actually is they are putting on their face everyday (and how it links to the science you learnt at GCSE).

One of my eyeshadow pallets that I must have had for YEARS (and could probs do with me checking both the chemistry and the expiration date!)

Cosmetics and make up actually have a very long history. They have been used for over 6000 years, dating back to both Ancient Egypt and Ancient China. Back then, both men and women typically used cosmetics to darken their eyelids and paint their nails. Nowadays make up, is everywhere, typically marketed at women to make them look "prettier". While there are a lot of issues within make up as a concept and the make up industry, that is not a topic to tackle today. Today we are looking purely at the chemicals (natural or not) that go into these products.

Cosmetic chemists are the scientists who research, develop, and test cosmetic and personal care products. They have to formulate the products, synthesise the chemicals, test them for stability and safety, and ensure they can be scaled up for production and large scale manufacturing. They work with all sorts pf products from sunscreen and skin care, to perfumes and make up. In this post I'm going to look at the chemicals behind just a few: highlight, mascara, eyeshadow, and lipstick .

1. Highlight

Highlight is typically a shinny powder or cream that is added to the cheekbones, nose, upper lip, and inner corner of the eye to accentuate the high points of the face. The main physics here is that it uses light reflecting minerals, and combines them with chemical binders and emulsions to form the powder or paste.

The light reflecting minerals are typically micas which are a silicate mineral with a natural cleavage (a natural break) that causes them to form thin flat sheets that can act like lots of tiny mirrors. It gets finely milled to maximise its reflectivity. Mostly natural micas are used (they are common rock forming minerals), but synthetic ones are also manufactured in labs to be perfectly uniform and smooth. Titanium dioxide is also sometimes used, it has a very high refractive index which means that it bends the light that shins through tit causing it to sparkle and, when combined with mica, causes that iridescent shimmer you see in highlight products. Titanium dioxide is also a key product used in sunscreens, and while no one is opting to cover their entire face in highlight to protect against UV (would be very Edward Cullen core), it is also added to sun screens to reflect off UV rays and protect your skin. Pearlescent pigments are often used for the same purpose as mics ad TiO2, to create that iridescent shiny look, bespoke to highlight.

Alongside these, iron oxides are added in specific ratios to change the undertone colour of the product, People often think of iron oxides as being a rusty red colour, but they can vary from white to champagne and bronze so are used to change the colour of the product. Sometimes silica (silicon dioxide) is also used, especially in highlights marketed at people with oily skin. The particles are spherical and help to absorb excess skin oil as well as evenly scattering light which gives a sort of blurring effect.

Structural binders are added to these minerals to keep them together and allow them to cling your face. Zinc and magnesium stearate are long hydrocarbon chains that make the product feel buttery and stick to the lipids on the surface of the skin. Emulsifiers (molecules with both a hydrophilic and hydrophobic side) are used to mix water-soluble, and oil-soluble ingredients together in cream and liquid highlighters. Humectants (moisture attracting substances) such as hyaluronic acid and glycerin are used to chemically bind water molecules from the air to the skin, which sis why you often hear of hyaluronic acid as a hydrating skin product.

Finally, emollients (moisturising substances) such as dimethicone and isododecane (or more familiar things like jojoba oil, and shea butter) are used to help the product blend. These chemicals are able to go into the microscopic spaces between dead skin cells which smoothes out the skins surface, giving that "dewy" look that is common to liquid and cream highlights. They also act as moisturisers which is great for dry skin.

2. Mascara

Mascara, used to darken the eyelashes and make them look longer, is primarily composed of pigments, oils, waxes, polymers, and preservatives. The composition also varies depending on if the product is waterproof or not.

The common pigments found in mascara are pure carbon (for deep black), iron oxides (for reddish-brown tints), and sulphur containing sodium silicate clays which can give a blue tint. Waxes and emollients are then added to make the mascara thick and help it stick to the lashes. A heavy base wax such as beeswax, paraffin, or palm wax is used to stiffen the lashes, alongside oils such as mineral, castor, and even sesame or linseed oils to manage texture. Petroleum derived polymers such as Polyvinyl Alcohol (PVA) are used to bind the mascara together and give a uniform coating. Microfibres of nylan or rayon are also added if a mascara is lengthening as these can physically build up the tips of your lashes. Solvents and emulsifiers are added (as are in many make up products) to allow oil and water soluble chemicals to mix evenly, and finally preservatives such as parabens, and phenoxyethanol are used as the mascara wand is constantly exposed to air (so needs to be prevented from oxidising) and microbes around your eyes (so needs to protected from fungal and bacterial growth).

Then we get into the waterproof (hydrophobic) vs non-waterproof (hydrophilic) element of mascaras. Hydrophilic mascaras will have chemicals that contain hydrogen bonds (such as ammonium acrylates and alcohols). As water is a polar molecule that forms hydrogen bonds (throwback to A-Level chem), it will form strong hydrogen bonds with the polar chemicals in the mascara meaning it can be dissolved in the water. On the other hand, hydrophobic mascaras have a lot of waxes and oils such as petroleum distillates, and glycerides that are non-polar and have carbon-hydrogen bonds. As they are non-polar, the compounds won't dissolve in water so need a non-polar substance (such as a special make up remover) to dissolve them. This is why its often so annoying to remove waterproof mascara, even with make up remover.

3. Eyeshadow

Eyeshadow is one of the oldest forms of makeup. Darkening the eyelids dates back to ancient times. Historically, a variety of things were used as eye shadows. Ancient Egyptians used crushed malachite mineral to add a pop of green to their eyelids, as well as powders made from golden pyrite and blue lapis lazuli. These were also used in ancient Greece and Rome, along with ash for a black hue. The Victorians are famous for using questionable things as eyeshadows, including toxic substances containing lead, mercury, and arsenic. Today, eyeshadows are made from a mixture of bases, pigments, binders, and preservatives.

The pigments used in eye shadows, much like ancient times, are often derived from earth minerals. Iron oxides are used to create reds, yellows, and blacks, and titanium dioxide, a bright white, is used as a pigment and for opacity. Synthetic pigments are also used, carbon black and synthetic coal tar dye have been used but face scrutiny around hypersensitivity and oxidative stress (so always read the label to see whats in your makeup before you just stick it on your face). Added to these pigments are base fillers such as talc and silica to make the eyeshadow powdery and able to spread evenly across the eyelid. Micas are also present, as they are in highlight, for a shimmery effect. Binders like silicones and mineral oils work to hold the dry powder particles together. Finally, preservatives are added, as with other make up products, such as parabens and phenoxyethanol to extend shelf life. Parabens are often avoided by clean beauty brands as there is some suggestion of them binding to hormone receptors and disrupting endocrine glands that produce hormones.

The final thing to he aware of (which shocked me a bit) is the presence of PFAS (per- and poly- fluoroalkyl compounds) which are commonly known as forever chemicals. I had come across these chemicals during my internship in the water industry and had researched how their strong carbon-fluorine bond means they don't break down in the environment and are very difficult to remove from drinking water supplies. PFAS may be added to water resistant or very metallic cream eyeshadows to makew them last longer, so once again - pllease check the labels of your make up.

One the other hand, more and more brands are starting to incorporate organic and natural ingredients into their products, aloe vera is a good example, which helps hydrate the skin around the eyes as well as being good for a smooth application. Green tea extract (which is packed with antioxidants) is also used in certain brands.

4. Lipstick

Lipstick is the final product I have done some research into. Its mainly made of oils, waxes, and colourants, with some preservatives for shelf life.

Oils such as castor oil, synthetic petrolatum and minerals oils are used a fluid bases in traditonal lipsticks.

Synthetic esters such as cetearyl isononanoate and isopropyl hydroxystearate work as wax softeners, and silicones such as dimethicone or cyclomethicone can be added to prevent it feeing greasy. Waxes are used as a structural matrix, thats why lipstick do feel waxy, hold their shape, and dont tend to melt. Beeswax, Carnabua wax, and Candelilla wax are all used.

The colour of lipsticks comes from pigments. Iron oxides are used for earthy tones such as red, brown, and flesh tones (as we have seen is common in make up products), and titanium and zinc oxides are used as their bright white can lighten vivid colours and make paler tints. Eosin is a dye that undergoes a chemical reaction with amino acids found in the skin and works to lock deep red stains onto the lips, this is what is found in lip staining products. Capsaicin (the spicy bit found in chilli peppers) is sometimes added to lip pluming products to iritate the skin and cause that plump look. Finally, silicas and clays are added to matte finish lipsticks to scatter light uniformly, or micas added to shimmery finishes to scatter light in different angles. These both work due to differences in mineral cleavage.

Lipsticks have a lot of biodegradable products in them (fats and oils) so need preservatives to protect from oxidation and microbial gortwh. As with the other produyts we have looked at, parabens, phenoxyethanol. and antioxidants suh as Vitamin E are often used.

So what have we learnt form all this? That the chemistry of make up is actually super complicated! So much science goes into the products filling the beauty counters at Boots and I think that that is pretty awesome! Also - read the labels of the products you own. Some of them may contain things such as PFAS and parabens that might not be the best for your body or the environment.

Further Reading :

• This is a great link if you want to dive deeper into chemical structures of parabens, emulsifiers, and alcohols! - https://chem.libretexts.org/Courses/Duke_University/CHEM_110_Honors_Writing_Projects/Duke_CHEM_110_Fall_2022%3A_Cox_and_Shorb/The_Chemistry_Behind_Cosmetics