The chemistry of cosmetics Private2 weeks ago - Real estate - Battambang - 9 views
Cosmetics materials are not a modern invention. Humans have used various substances to alter their appearance or accentuate their features for at least 10,000 years, and possibly a lot longer.
Women in Ancient Egypt used kohl, a substance containing powdered galena (lead sulphide—PbS) to darken their eyelids, and Cleopatra is said to have bathed in milk to whiten and soften her skin. By 3000 B.C men and women in China had begun to stain their fingernails with colours according to their social class, while Greek women used poisonous lead carbonate (PbCO3) to achieve a pale complexion. Clays were ground into pastes for cosmetic use in traditional African societies and indigenous Australians still use a wide range of crushed rocks and minerals to create body paint for ceremonies and initiations.
Cosmetic products that make an additional therapeutic claim (such as moisturisers that also lighten the skin) are regulated by a different organisation—the Therapeutic Goods Administration (TGA).
But what exactly are we putting on our skin? What do those long names on the ingredient list mean and what do they do? While the formula of each product differs slightly, most cosmetics contain a combination of at least some of the following core ingredients: water, emulsifier, preservative, thickener, emollient, colour, flavors and fragrances and pH stabilisers.
If your product comes in a bottle, chances are the first ingredient on the list is going to be water. That’s right, good old H2O. Water forms the basis of almost every type of cosmetic product, including creams, lotions, makeup, deodorants, shampoos and conditioners. Water plays an important part in the process, often acting as a solvent to dissolve other ingredients and forming emulsions for consistency.
Water used in the formulation of cosmetic materials is not your everyday, regular tap water. It must be ‘ultra-pure’—that is, free from microbes, toxins and other pollutants. For this reason your label may refer to it as distilled water, purified water or just aqua.
The term emulsifiers refers to any ingredient that helps to keep unlike substances (such as oil and water) from separating. Many cosmetic products are based on emulsions—small droplets of oil dispersed in water or small droplets of water dispersed in oil. Since oil and water don't mix no matter how much you shake, blend or stir, emulsifiers are added to change the surface tension with surfactant materials between the water and the oil, producing a homogeneous and well-mixed product with an even texture. Examples of emulsifiers used in cosmetics include polysorbates, laureth-4, and potassium cetyl sulfate.
Preservatives are important ingredients. They are added to cosmetics to extend their shelf life and prevent the growth of microorganisms such as bacteria and fungi, which can spoil the product and possibly harm the user. Since most microbes live in water, the preservatives used need to be water-soluble, and this helps to determine which ones are used. Preservatives used in cosmetics can be natural or synthetic (man-made), and perform differently depending on the formulation of the product. Some will require low levels of around 0.01%, while other will require levels as high as 5%.
Some of the more popular preservatives include parabens, benzyl alcohol, salicylic kojic acid, formaldehyde and tetrasodium EDTA (ethylenediaminetetra-acetic acid).Lipid thickeners are usually solid at room temperature but can be liquefied and added to cosmetic emulsions. They work by imparting their natural thickness to the formula. Examples include cetyl alcohol, stearic acid and carnauba wax.
Emollients soften the skin by preventing water loss. They are used in a wide range of lipsticks, lotions and cosmetics. A number of different natural and synthetic chemicals work as emollients, including beeswax, olive oil, coconut oil and lanolin, as well as petrolatum (petroleum jelly), mineral oil, almond oil, glycerine, zinc oxide, butyl stearate and diglycol laurate.
The inorganic metal oxide pigments are usually duller than the organic intermediate pigments, but are more resistant to heat and light, providing a longer-lasting colour.
Glimmer and shine