Cosmetic chemistry: the science behind your lotions and potions
Cosmetic products are packed with chemical science, but do they live up to the hype?
Proteins are the major building blocks of the human body and collagen and elastin are two critical types found in skin. They form a web-like scaffold that holds skin cells in place; collagen provides structure and elastin provides springiness. However, as we get older, we produce less and less of both, and skin starts to lose its firm, flexible texture. One solution employed by cosmetics giants is to add fragments of protein to their creams. This helps to smooth out wrinkles, but probably not in the way you were expecting. Rather than repairing the collagen and elastin scaffolding, the fragments work by improving skin texture from the outside. They go on damp and flexible, and as they dry out they tighten up. This tugs on the skin beneath, temporarily smoothing out the wrinkles.
Mattifying makeup products attempt to minimise shine by including ingredients that absorb oil and water. Clays are made from oxygen or oxygen and hydrogen (hydroxyl groups) and arranged into crystals with four or eight sides. At the centre of each is an atom of silicon or aluminium. These structures form sheets, and it’s between these sheets that oil and water become trapped. Mattifying agents can be found in a variety of products, including powders, foundations, lotions, balms, gels and sprays. Silicone elastomers are a synthetic alternative. They are made from chains of silicone, carbon, hydrogen and oxygen strung together to form branching webs. These expand when liquids are added, helping to lock moisture away.
Whitening toothpastes work like a rough polish, using abrasive grains to scrape away the film of bacteria and pigments that continually builds on the surface of the enamel. However, they can’t change the colour of the teeth beneath. For teeth whiter than a natural shade, chemical bleaching is the only option. Whitening strips contain carbamide peroxide, which breaks down chromophores, the parts of molecules responsible for their colour.
Mascara colours the eyelashes using pigments like carbon black (made by the incomplete burning of petrochemicals) and iron oxides (which come in varying shades of red and brown). For ease of application, they are suspended in oils, waxes and water, forming a paste that can be spread onto the lashes with a brush. These carriers include beeswax, shellac (a type of resin made by lac bugs), lanolin (from sheep) and paraffin. Waterproof mascaras tend to contain more waxes and oils than their water soluble counterparts, helping them to resist moisture and stay on the lashes longer. But, because they’ve been designed not to dissolve in water, they can be a challenge to wash off. Oily makeup removers help to dissolve the waxy carriers that stick the pigments to the lashes. The mascaras themselves sometimes contain lubricants, like glyceryl stearate, which help the mixture to stay slippy.
The skin is in a constant state of renewal, and as new skin cells are made, the old ones flake away. Exfoliators help to rub these from the surface, making the skin look smoother and brighter. The textured surface of a washcloth is enough to gently scrub away some of the surface cells, but many treatments offer a deeper cleanse. Exfoliating washes contain tiny fragments of sugar, crushed nut shells or plastic that act as abrasives. Chemical peels use acids (commonly salicylic or lactic acid) to create a controlled burn, and microdermabrasion uses a rough rotating brush to scrape away even more of the skin’s surface.
The glitter and sheen in eyeshadows and highlighters is most commonly mica or bismuth oxychloride. Mica bends the light as it hits, while bismuth oxychloride has a pearlescent appearance. If mica is combined with titanium dioxide the way it reflects light changes, creating iridescent shades.
Primers contain lots of ingredients that aim to keep makeup looking fresh all day. Silicones help to absorb moisture and oils, while waxes and polymers form a bridge that sticks cosmetics to the skin. Spherical silicone molecules coated with titanium dioxide help to diffuse light, evening out blemishes and creating an ‘airbrushed’ look.
This article was originally published in How It Works issue 99, written by Laura Mears
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